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Psychedelics not linked to mental health problems or suicidal behavior: A population study

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A recent large population study of 130,000 adults in the United States failed to find evidence for a link between psychedelic use (lysergic acid diethylamide, psilocybin or mescaline) and mental health problems. Using a new data set consisting of 135,095 randomly selected United States adults, including 19,299 psychedelic users, we examine the associations between psychedelic use and mental health. After adjusting for sociodemographics, other drug use and childhood depression, we found no significant associations between lifetime use of psychedelics and increased likelihood of past year serious psychological distress, mental health treatment, suicidal thoughts, suicidal plans and suicide attempt, depression and anxiety. We failed to find evidence that psychedelic use is an independent risk factor for mental health problems. Psychedelics are not known to harm the brain or other body organs or to cause addiction or compulsive use; serious adverse events involving psychedelics are extremely rare. Overall, it is difficult to see how prohibition of psychedelics can be justified as a public health measure. © The Author(s) 2015.
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DOI: 10.1177/0269881114568039
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Introduction
The classical psychedelics lysergic acid diethylamide (LSD),
psilocybin (magic mushrooms) and mescaline (peyote and other
cacti) have their primary mechanism of action at the serotonin 2A
(5-HT2A) receptor, elicit similar, often indistinguishable effects
and show cross-tolerance (Bonson, 2012). Over 30 million adults
in the United States (US) have tried psychedelics (approximately
one in six adults aged 21–64 years) (Krebs and Johansen, 2013a).
Psychedelics are not known to harm the brain or other body
organs or to cause addiction or compulsive use (Halberstadt,
2015; Bonson, 2012). Psychedelics are well known for inducing
profound effects on the mind, which sometimes include confu-
sion and emotional turmoil (McWilliams and Tuttle, 1973). Both
the European Monitoring Center for Drugs and Drug Addiction
(EMCDDA) and the health authorities in the Netherlands, where
hundreds of thousands of servings of psilocybin mushrooms are
legally sold in shops each year, report that serious injuries related
to psychedelics are extremely rare (EMCDDA, 2011; CAM,
2007). Furthermore, Dutch police report that legal sale of psilo-
cybin mushrooms has not led to public order problems (Van
Amsterdam et al., 2011). Approximately 0.005% of emergency
department visits in the US involve LSD or psilocybin (US
Department of Health and Human Services, Substance Abuse
and Mental Health Services Administration, Center for
Behavioral Health Statistics and Quality 2013; Centers for
Disease Control and Prevention (CDC), 2014). Drug abuse
experts consistently rank LSD and/or psilocybin mushrooms as
much less harmful to the individual user and to society compared
to alcohol and other controlled substances (Nutt et al., 2007,
2010; Taylor et al., 2012; van Amsterdam et al., 2010). Controlled
studies have not linked either clinical administration or regular
use of psychedelics in religious ceremonies to lasting health
problems (see Krebs and Johansen, 2013b).
Psychedelics often elicit deeply personally and spiritually mean-
ingful experiences and sustained beneficial effects (Carhart-Harris
and Nutt, 2010; Griffiths et al., 2008, 2011; Morgan et al., 2010).
Common reasons for using psychedelics include mystical experi-
ences and personal development (Hallock et al., 2005). Indeed, in
many countries, including the US, select groups have protection
from prosecution on grounds of freedom of belief or religion.
People have used psychedelics for at least 5700 years (Bruhn et al.,
2002), pre-dating the major organized religions. Modern anti-
psychedelic legislation began 100 years ago when members of rival
religious groups campaigned against Native American peyote use,
calling peyote addictive and an ‘insidious evil’ that causes users to
‘withdraw from the churches and become “peyote worshipers”’
(Newberne and Burke, 1922). Eventually, concerned scientists
defended peyote users, using evidence-based reasoning and human
rights arguments (Collier, 1952; La Barre et al., 1951; Le Farge,
1960); this led to legal exemptions for specific groups. However,
laws and cultural biases against peyote remained in place and were
later extended to include other psychedelics. Concerns have been
Psychedelics not linked to mental health
problems or suicidal behavior: A population
study
Pål-Ørjan Johansen1 and Teri Suzanne Krebs2
Abstract
A recent large population study of 130,000 adults in the United States failed to find evidence for a link between psychedelic use (lysergic acid
diethylamide, psilocybin or mescaline) and mental health problems. Using a new data set consisting of 135,095 randomly selected United States adults,
including 19,299 psychedelic users, we examine the associations between psychedelic use and mental health. After adjusting for sociodemographics,
other drug use and childhood depression, we found no significant associations between lifetime use of psychedelics and increased likelihood of past
year serious psychological distress, mental health treatment, suicidal thoughts, suicidal plans and suicide attempt, depression and anxiety. We failed
to find evidence that psychedelic use is an independent risk factor for mental health problems. Psychedelics are not known to harm the brain or other
body organs or to cause addiction or compulsive use; serious adverse events involving psychedelics are extremely rare. Overall, it is difficult to see
how prohibition of psychedelics can be justified as a public health measure.
Keywords
Psychedelic, hallucinogen, epidemiology, public health, suicide
1
EmmaSofia, Oslo, Norway
2
Department of Neuroscience, Norwegian University of Science and
Technology, Trondheim, Norway
Corresponding author:
Teri Suzanne Krebs, Department of Neuroscience, Norwegian University
of Science and Technology, Trondheim, N-7489, Norway.
Email: krebs@ntnu.no
568039JOP0010.1177/0269881114568039Journal of PsychopharmacologyJohansen and Krebs
research-article2015
Original Paper
2 Journal of Psychopharmacology
raised that the ban on use of psychedelics is a violation of the human
rights to belief and spiritual practice, full development of the per-
sonality, and free time and play (United Nations General Assembly,
1948; Walsh, 2014).
There is increasing interest in the therapeutic use of psyche-
delics, especially for alcoholism (Krebs and Johansen, 2012),
smoking cessation (Johnson et al., 2014), depression and other
mental health problems (Baumeister et al., 2014; Bogenschutz,
2013; Hendricks et al., 2014). David Nutt and colleagues have
explained how national and international regulations have impeded
scientific research and medical treatment development with psych-
edelics and other highly controlled ‘Schedule I’ substances (Nutt
et al., 2013). Prohibition has also obviously had negative conse-
quences for the millions of individuals who find it worthwhile to
use these substances in various cultural settings outside of the clinic.
Our previous population study failed to find evidence for a
link between psychedelic use (lifetime use of LSD, psilocybin,
mescaline, or peyote, past year use of LSD) and past year serious
psychological distress, receiving or needing mental health treat-
ment, or symptoms of eight psychiatric diagnoses, including
major depression, anxiety disorders, mania and psychosis, or
visual hallucinations (Krebs and Johansen, 2013b). Here, using a
new large data set, which included data on suicidal thoughts and
suicide attempt, we again examine the associations between the
use of psychedelics and mental health.
Materials and methods
Source, population and data
The annual National Survey on Drug Use and Health (NSDUH)
collects data on substance use and mental health from a random
sample representative of the US civilian non-institutionalized
population (http://oas.samhsa.gov/nsduh.htm). We pooled data
from respondents aged 18 years and over from survey years
2008–2011. Half of year 2008, earlier survey years and younger
respondents were not pooled due to questionnaire differences
(including no questions on suicidal behavior). The response rate
was 78%. In addition, approximately 10% of participants were
excluded from the public use data file, either because of excessive
missing data on drug use or because they were excluded at ran-
dom in order to increase anonymity. The sample consisted of
135,095 respondents, of whom 19,299 (13.6% weighted) reported
lifetime use of a psychedelic substance. Our previous study exam-
ined NSDUH years 2001–2004 (Krebs and Johansen, 2013b).
Use of psychedelics
We counted participants as having any lifetime psychedelic use if
they reported use of LSD, psilocybin, mescaline or peyote. LSD,
psilocybin and mescaline are all classical serotonergic psychedelics
with main mechanism of action at the 5-HT2A receptor (Halberstadt,
2015). We combined mescaline and peyote (mescaline-containing
cactus) use into one variable but also examined peyote use sepa-
rately. Data on past year use was available only for LSD.
Mental health indicators
We examined 11 self-reported indicators of past year mental
health problems. Past year mental health indicators also used in
our previous study (Krebs and Johansen, 2013b) were serious
psychological distress during the worst month of the past year,
assessed with the K6 scale (Kessler et al., 2003a), mental health
treatment, including treatment for substance disorders (inpatient,
outpatient, psychiatric medication prescription, felt a need for but
did not receive mental health treatment). The remaining mental
health indicators from our previous study, such as psychosis
symptoms, were not available in this data set. Past year mental
health indicators new to this study were suicide thoughts, suicide
plan, suicide attempt, symptoms of major depressive episode
(assessed with a questionnaire adapted from the National
Comorbity Survey (Kessler et al., 2003b), which was different
from the depression questionnaire in our previous study), physi-
cian diagnosis of depression, and physician diagnosis of an anxi-
ety disorder.
The K6 scale provides a valid assessment of general psycho-
logical distress during the worst month of the past year. It covers
types of psychological distress that are common to a broad range
of psychiatric disorders and has strong accuracy in discriminat-
ing between people with and without one or more diagnoses from
the Diagnostic and Statistical Manual of Mental Disorders,
Fourth Edition (American Psychiatric Association, 1994; Kessler
et al., 2010).
Control variables
Control variables consisted of a variety of sociodemographic,
psychological and drug use variables (Figure 1, Tables 1 and 2).
The control variables were selected on the basis of associations
with mental health in previous research, and were the same as
those used in our previous study, with two differences: depres-
sive episode before age 18 was now available to be included as
a control variable in this study, and lifetime exposure to an
extremely stressful event was not available to be included.
The control variables were age at interview (11 categories,
treated as a continuous variable), gender (male, female), race/eth-
nicity (white, Hispanic, black, Asian, Native American, Native
Hawaiian or Pacific Islander, more than one), household income
(less than US$20,000, US$20,000–49,999, US$50,000–74,999,
US$75,000 or more), education (not high school graduate, high
school graduate, some college, college graduate), marital status
(unmarried, married), likes to test self by doing risky things
(never, seldom, sometimes, always), depressive episode before
age 18 years (no, yes), and 10 types of lifetime drug use (cannabis/
marijuana, opiates, cocaine, sedatives/tranquilizers, stimulants,
MDMA/ecstasy, inhaled anesthetics, amyl nitrates, other inhal-
ants, phencyclidine). Additionally, in the analyses of past year use
of LSD we also included as control variables past year use of the
other drugs listed above, but with only one variable for any past
year inhalant use because data on specific inhalants were not
available.
Data analysis
We used multivariate logistic regression to calculate adjusted
odds ratio (aOR) associations between mental health variables
and lifetime use of any psychedelics, lifetime use of the specific
psychedelics (LSD, psilocybin, mescaline/peyote, peyote) and
past year use of LSD. We also calculated associations between
mental health and use of any psychedelics in subgroups stratified
on sex, age (18–25 years, 26 or older), past year illicit drug use
and depressive episode before age 18.
Johansen and Krebs 3
All unstratified analyses had 25 or more events per control
variable, and all stratified analyses had eight or more events per
control variable (Vittinghoff and McCulloch, 2007). For all con-
trol variables the variance inflation factors were under 2.5, indi-
cating little multi-collinearity.
Participants with missing data were excluded; including par-
ticipants with missing values had no effect on statistical signifi-
cance. All calculations accounted for the NSDUH weighting
variables and complex sample design. We used SPSS/PASW
Statistics (version 18.0.3).
Results
Psychedelic users were more likely than non-users to report a
depressive episode before age 18. They were also more likely to
be younger, male, white, unmarried, with somewhat more educa-
tion and income, to like doing risky things and to have used other
drugs (Tables 1 and 2).
Lifetime psychedelic use
Lifetime psychedelic use was not associated with any of the indi-
cators of mental health problems (aOR range 0.7–1.1). Rather,
lifetime psychedelic use was associated with a lower likelihood
of past year inpatient mental health treatment (aOR 0.8, 95%
confidence interval (CI) 0.6–0.9, p = 0.01) (Figure 1, Table 3). In
our previous study this association was not statistically signifi-
cant (aOR 0.9, 95% CI 0.7–1.2, p = 0.53). Including respondents
with missing data (with missing values set to the most common
response) or excluding Native Americans (who may use peyote
in a religious setting) did not substantially change the results.
Specific psychedelic use
Among the specific psychedelics (lifetime use of LSD, psilocy-
bin, mescaline/peyote or peyote; past year use of LSD), we found
10 associations with a lower likelihood and one association with
a greater likelihood of mental health problems (Table 4). Four of
these associations were also statistically significant in our previ-
ous population study.
Associations between psilocybin use and lower likelihood of
past year serious psychological distress, inpatient mental health
treatment and psychiatric medication prescription were statisti-
cally significant both in this study (aOR 0.9, p = 0.007; aOR 0.7,
p = 0.0004; aOR 0.8, p = 0.002, respectively) and in our previous
study (aOR 0.8, p = 0.009; aOR 0.8, p = 0.04; aOR 0.8, p =
0.00008, respectively) (Krebs and Johansen, 2013b). Past year
use of LSD was, with weak statistical significance, associated
with lower likelihood of serious psychological distress (aOR 0.8,
p = 0.04); this was also consistent with our previous study (aOR
0.7, p = 0.009).
Mescaline/peyote use was, with weak statistical significance,
associated with a greater likelihood of past year symptoms of
major depressive episode (aOR 1.2, p = 0.02); however, mesca-
line/peyote use was not associated with diagnosis of depression
(aOR 1.0, p = 0.59) and peyote (mescaline-containing cactus) use
was not associated with either symptoms of major depressive
episode or diagnosis of depression (aOR 1.1, p = 0.24; aOR 0.9,
p = 0.60, respectively). Furthermore, in our previous study, nei-
ther mescaline/peyote use nor peyote use was associated with
past year symptoms of major depressive episode (aOR 0.9, p =
0.14; aOR 0.9, p = 0.67, respectively).
Stratified subgroups
In the stratified subgroups there were eight associations between
psychedelic use and a decreased likelihood of various past year
mental health problems, most with weak statistical significance,
and none consistent with the stratified subgroups in our previous
population study (Table 5). Notably, among people with a history
of childhood depressive episode (before age 18 years), psyche-
delic use was associated with a lower likelihood of suicidal
thoughts (aOR 0.8, p = 0.01) and suicidal plan (aOR 0.5, p =
0.002). Data on childhood depression and past year suicidal
behavior were not available in our previous population study.
Discussion
Lack of associations with mental health or
suicidality
We failed to find any associations between lifetime use of psych-
edelics and past year serious psychological distress, receiving or
needing mental health treatment, depression, anxiety, or suicidal
thoughts or behavior in the past year. Rather, lifetime use of
Figure 1. Association between psychedelic use and mental health.
aOR: adjusted odds ratio. Values less than 1.0 indicate lower likelihood among
people with lifetime psychedelic use, adjusted for age (11 categories, treated as
a continuous variable), gender (male, female), race/ethnicity (white, Hispanic,
black, Asian, Native American, Native Hawaiian or Pacific Islander, more than
one), household income (less than US$20,000, US$20,000–49,999, US$50,000–
74,999, US$75,000 or more), education (not high school graduate, high school
graduate, some college, college graduate), marital status (unmarried, married),
likes to test self by doing risky things (never, seldom, sometimes, always),
depressive episode before age 18 years (no, yes), and 10 types of lifetime drug
use (cannabis/marijuana, opiates, cocaine, sedatives/tranquilizers, stimulants,
MDMA/ecstasy, inhaled anesthetics, amyl nitrates, other inhalants, phencycli-
dine); CI: confidence interval.
4 Journal of Psychopharmacology
psychedelics was associated with decreased inpatient psychiatric
treatment. In addition to not being significantly different from no
association, in all cases the calculated aORs were small (for all,
psychedelic use aOR < 1.2).
Stratifying by age, gender, past year illicit drug use or child-
hood depressive episode did not substantially change the results
of any of the logistic regression analyses. Likewise, lifetime use
of LSD, psilocybin, mescaline or peyote, or past year use of LSD
was not associated with a higher rate of mental health problems.
Most claims about the harms from psychedelics have been
based on theoretical assumptions and case reports, which should
be evaluated with caution. See our earlier population study of
mental health among psychedelic users for further discussion
about case reports and previous studies (Krebs and Johansen,
2013b).
The idea of ‘flashbacks’ and ‘hallucinogen
persisting perceptual disorder’
In particular, our previous population study (Krebs and Johansen,
2013b) did not support either the idea of ‘flashbacks’, described
in extreme cases as recurrent psychotic episodes, hallucinations,
or panic attacks, or the more recent ‘hallucinogen persisting per-
ceptual disorder’ (HPPD), described as persistent visual phenom-
ena with accompanying anxiety and distress, since lifetime use of
psychedelics and past year use of LSD was not associated with
past year symptoms of visual phenomena (‘seeing something
others could not’), panic attacks, psychosis or overall serious
psychological distress. Recent randomized controlled trials with
psilocybin have not reported any cases of flashbacks or persistent
visual phenomena (Griffiths et al., 2008, 2011; Studerus et al.,
Table 1. Sociodemographic and psychological variables.
Ever used psychedelics Never used psychedelics % used psychedelics
wt% N wt% N wt%
Total 100% 19,299 100% 115,796 13.6%
Age
18–25 years 13.8% 8609 14.9% 58,284 12.7%
26 years or older 86.2% 10,690 85.1% 57,512 13.7%
Sex
Male 63.0% 11,625 45.9% 51,625 17.7%
Female 37.0% 7674 54.1% 64,171 9.7%
Race/ethnicity
White 83.7% 15,556 65.5% 70,327 16.7%
Hispanic 8.1% 1705 14.9% 19,285 7.9%
Black 3.8% 531 12.7% 16,234 4.5%
Asian 1.3% 239 5.1% 4792 3.8%
Native American 1.0% 484 0.4% 1545 27.4%
Native Hawaiian or Pacific Islander 0.2% 46 0.4% 568 7.2%
More than one 1.9% 738 1.1% 3045 22.2%
Household income
Less than US$20,000 16.5% 4613 18.6% 30,113 12.3%
US$20,000–49,999 30.1% 6638 33.3% 39,898 12.4%
US$50,000–74,999 18.2% 3127 17.2% 18,355 14.3%
US$75,000 or more 35.2% 4921 31.0% 27,430 15.2%
Education
Not high school graduate 11.3% 2833 15.3% 19,407 10.4%
High school graduate 28.1% 6001 31.0% 38,256 12.5%
Some college 30.5% 6207 24.9% 33,361 16.2%
College graduate 30.0% 4258 28.8% 24,753 14.1%
Marital status
Not married 52.5% 13,129 45.4% 74,077 15.4%
Married 47.5% 6163 54.6% 41,697 12.0%
Likes to test self by doing risky things
Never 27.6% 4278 55.6% 53,388 7.3%
Seldom 44.7% 8258 32.4% 41,114 17.9%
Sometimes 25.0% 5871 11.0% 18,742 26.4%
Always 2.7% 871 1.1% 2266 28.3%
Depressive episode before age 18
No 92.5% 17,067 97.1% 108,628 13.0%
Yes 7.5% 1961 2.9% 5923 29.2%
wt%: weighted percentage.
Johansen and Krebs 5
2011). Interviews with over 500 regular participants in Native
American peyote ceremonies did not identify anyone with flash-
backs or persistent visual symptoms (Halpern et al., 2005).
Occasional visual phenomena are common in the general popula-
tion, and all of the symptoms included in the purported HPPD are
also present in people who have never used psychedelics. A
Table 2. Lifetime illicit drug use variables.
Ever used psychedelics Never used psychedelics % used psychedelics
wt% N wt% N wt%
Total 100% 19,299 100% 115,796 13.6%
Psychedelics
LSD 74.9% 12,806 0% 0 100%
Psilocybin 66.7% 14,438 0% 0 100%
Mescaline/peyote 33.0% 4595 0% 0 100%
Peyote 17.6% 2512 0% 0 100%
Other drugs
Cannabis 97.8% 18,899 36.0% 48,411 29.9%
Opiates 49.7% 11,223 9.5% 15,371 45.2%
Cocaine 71.3% 13,092 7.5% 8499 60.0%
Tranquilizers and sedatives 43.5% 8688 5.6% 7446 55.1%
Stimulants 37.5% 7109 3.7% 5092 61.4%
MDMA 32.9% 8407 2.0% 4119 32.9%
Inhaled anesthetics 28.6% 5893 1.5% 2515 74.4%
Alkyl nitrites 16.0% 2401 1.1% 1155 70.1%
Other inhalants 12.3% 2524 1.7% 2931 53.3%
PCP 17.7% 2567 0.4% 404 17.7%
wt%: weighted percentage.
Table 3. Association of psychedelic use with mental health.
Ever used
psychedelics
Never used
psychedelics
aORa (95% CI) p
N N
Serious psychological distress in worst month of past year
K6 scale 4165 15,525 0.9 (0.8–1.0) 0.12
Mental health treatment in past year
Inpatient 694 1349 0.8 (0.6–0.9) 0.01
Outpatient 3108 8343 1.0 (0.9–1.1) 0.87
Medication 3472 11,282 1.0 (0.9–1.1) 0.77
Needed but did not receive 2534 6990 1.0 (0.9–1.1) 0.56
Suicidal thought and behavior in past year
Thought about killing self 1748 5533 0.9 (0.8–1.0) 0.19
Planned to kill self 527 1654 0.8 (0.6–1.0) 0.09
Attempted to kill self 266 904 0.7 (0.5–1.0) 0.09
Depression and anxiety in past year
Symptoms of major depressive episode 2446 8178 1.0 (0.9–1.2) 0.81
Diagnosis of depression 2352 7648 1.0 (0.8–1.1) 0.55
Diagnosis of an anxiety disorder 2095 5747 1.1 (0.9–1.2) 0.39
aOR: adjusted odds ratio (values less than 1.0 indicate lower likelihood); CI: confidence interval.
Bold text indicates p < 0.05.
a
Adjusted for age (11 categories, treated as a continuous variable), gender (male, female), race/ethnicity (white, Hispanic, black, Asian, Native American, Native Hawai-
ian or Pacific Islander, more than one), household income (less than US$20,000, US$20,000–49,999, US$50,000–74,999, US$75,000 or more), education (not high
school graduate, high school graduate, some college, college graduate), marital status (unmarried, married), likes to test self by doing risky things (never, seldom,
sometimes, always), depressive episode before age 18 years (no, yes), and 10 types of lifetime drug use (cannabis/marijuana, opiates, cocaine, sedatives/tranquilizers,
stimulants, MDMA/ecstasy, inhaled anesthetics, amyl nitrates, other inhalants, phencyclidine).
6 Journal of Psychopharmacology
recent study of 120 US adults troubled by HPPD-like persistent
visual symptoms found a lower than average rate of psychedelic
use (Schankin et al., 2014). Overall, the validity of the HPPD
diagnosis remains scant. HPPD may fit within the somatic symp-
tom disorders. For further discussion, see Krebs and Johansen
(2013b).
Table 4. Association between use of LSD, psilocybin, mescaline and peyote and mental health.
LSD Psilocybin Mescaline/peyote Peyote LSD past year
aORa (95% CI) paORa (95% CI) paORa (95% CI) paORa (95% CI) paORb (95% CI) p
Serious psychological distress in worst month of past year
K6-scale 0.9 (0.8–1.1) 0.38 0.9 (0.8–1.0) 0.007 0.9 (0.8–1.1) 0.37 0.8 (0.7–1.0) 0.05 0.8 (0.6–1.0) 0.04
Mental health treatment in past year
Inpatient 0.8 (0.6–1.0) 0.02 0.7 (0.5–0.8) 0.0004 0.7 (0.6–0.9) 0.01 0.7 (0.5–1.0) 0.03 0.5 (0.3–0.8) 0.002
Outpatient 0.9 (0.8–1.0) 0.09 0.9 (0.8–1.1) 0.27 1.0 (0.9–1.2) 0.50 1.0 (0.8–1.2) 0.94 0.7 (0.5–0.9) 0.01
Medication 1.0 (0.9–1.2) 0.69 0.8 (0.7–0.9) 0.002 1.0 (0.9–1.1) 0.67 0.9 (0.8–1.1) 0.32 0.9 (0.6–1.2) 0.36
Needed but did not
receive
0.9 (0.8–1.1) 0.21 1.0 (0.9–1.1) 0.835 1.1 (0.9–1.3) 0.28 0.9 (0.7–1.1) 0.35 0.9 (0.7–1.2) 0.59
Suicidal thought and behavior in past year
Thought about killing
self
0.9 (0.8–1.0) 0.07 1.0 (0.8–1.2) 0.95 1.0 (0.8–1.3) 0.78 0.9 (0.7–1.1) 0.31 0.9 (0.6–1.3) 0.68
Planned to kill self 0.8 (0.6–1.0) 0.06 0.9 (0.7–1.3) 0.71 1.0 (0.7–1.5) 0.79 0.7 (0.5–1.1) 0.12 1.1 (0.7–1.7) 0.80
Attempted to kill self 0.8 (0.5–1.2) 0.25 0.9 (0.6–1.3) 0.44 1.0 (0.7–1.6) 0.83 0.7 (0.4–1.2) 0.21 0.6 (0.2–1.7) 0.35
Depression and anxiety in past year
Symptoms of major
depressive episode
1.0 (0.8–1.2) 0.94 1.0 (0.8–1.2) 0.70 1.2 (1.0–1.5) 0.02 1.1 (0.9–1.4) 0.24 1.1 (0.8–1.4) 0.75
Diagnosis of depres-
sion
0.9 (0.8–1.1) 0.29 0.8 (0.7–1.0) 0.01 1.0 (0.8–1.1) 0.59 0.9 (0.8–1.2) 0.60 0.9 (0.6–1.3) 0.60
Diagnosis of an anxi-
ety disorder
1.1 (0.9–1.3) 0.30 0.9 (0.8–1.1) 0.51 1.1 (0.9–1.4) 0.21 0.9 (0.7–1.1) 0.37 1.1 (0.7–1.5) 0.78
aOR: adjusted odds ratio (values less than 1.0 indicate lower likelihood); CI: confidence interval.
Bold text indicates p < 0.05.
a
Adjusted for age (11 categories, treated as a continuous variable), gender (male, female), race/ethnicity (white, Hispanic, black, Asian, Native American, Native Hawai-
ian or Pacific Islander, more than one), household income (less than US$20,000, US$20,000–49,999, US$50,000–74,999, US$75,000 or more), education (not high
school graduate, high school graduate, some college, college graduate), marital status (unmarried, married), likes to test self by doing risky things (never, seldom,
sometimes, always), depressive episode before age 18 years (no, yes), and 10 types of lifetime drug use (cannabis/marijuana, opiates, cocaine, sedatives/tranquilizers,
stimulants, MDMA/ecstasy, inhaled anesthetics, amyl nitrates, other inhalants, phencyclidine).
b
Adjusted for above variables plus nine types of past year drug use (cannabis/marijuana, opiates, cocaine, sedatives/tranquilizers, stimulants, MDMA/ecstasy, inhalants,
phencyclidine).
Table 5. Association of psychedelic use and mental health in stratified subgroups. Only results with p < 0.05 are shown.
Subgroup Past year mental health indicator aORa (95% CI) p
Female Inpatient mental health treatment 0.7 (0.5–0.9) 0.01
Age 18–25 Serious psychological distress 0.9 (0.8–1.0) 0.008
Age 18–25 Psychiatric medication 0.8 (0.7–1.0) 0.03
Age 18–25 Attempted to kill self 0.7 (0.6–1.0) 0.03
Age 26 or older Inpatient mental health treatment 0.8 (0.7–1.0) 0.04
No past year illicit drug use Attempted to kill self 0.5 (0.2–0.9) 0.04
No depression before age 18 Inpatient mental health treatment 0.8 (0.6–0.9) 0.02
Depression before age 18 Thought about killing self 0.8 (0.6–0.9) 0.01
Depression before age 18 Planned to kill self 0.5 (0.4–0.8) 0.002
aOR: adjusted odds ratio (values less than 1.0 indicate lower likelihood); CI: confidence interval.
a
Adjusted for age (11 categories, treated as a continuous variable), gender (male, female), race/ethnicity (white, Hispanic, black, Asian, Native American, Native Hawai-
ian or Pacific Islander, more than one), household income (less than US$20,000, US$20,000–49,999, US$50,000–74,999, US$75,000 or more), education (not high
school graduate, high school graduate, some college, college graduate), marital status (unmarried, married), likes to test self by doing risky things (never, seldom,
sometimes, always), depressive episode before age 18 years (no, yes), and 10 types of lifetime drug use (cannabis/marijuana, opiates, cocaine, sedatives/tranquilizers,
stimulants, MDMA/ecstasy, inhaled anesthetics, amyl nitrates, other inhalants, phencyclidine).
Johansen and Krebs 7
Psychedelics and personally significant
experiences
Our results might reflect beneficial effects of psychedelic use,
relatively better initial mental health among people who use
psychedelics or chance ‘false positive’ findings. However, it is
well documented that psychedelics elicit spiritual experiences.
Indeed, long-term psychological benefits have been reported in
several clinical trials of LSD, for example, ‘About half of the
total sample felt they had achieved more understanding and
acceptance of themselves and a broader tolerance of the view
points of others via the LSD experience’ (McGlothlin and Arnold,
1971). In a recent randomized controlled trial of psilocybin, most
of the participants (67%) regarded the experience as one of the
most personally significant moments in their lives (comparable
to the birth of a first child) (Griffiths et al., 2006) and, further-
more, most of the participants (64%) reported improved well-
being or life satisfaction 14 months later (Griffiths et al., 2006,
2008; MacLean et al., 2011). People often report long-term ben-
efits from LSD use (Morgan et al., 2010). No serious adverse
events have been reported in recent randomized controlled trials
of psilocybin, demonstrating that psychedelics can be adminis-
tered safely in medical contexts (Griffiths et al., 2008, 2011;
Johnson et al., 2008; Studerus et al., 2011). Case–control and
longitudinal studies have not found evidence of increased mental
health problems among people who have used traditional psych-
edelics (peyote or ayahuasca) hundreds of times in legally recog-
nized religious ceremonies (Bouso et al., 2012; Halpern et al.,
2005).
Limitations
This study had a retrospective, cross-sectional design, making it
impossible to draw causal inferences. Many potentially impor-
tant risk factors, such as family mental health history, were not
available. Longitudinal data were not available on mental health
or other factors before psychedelic use. We cannot exclude the
possibility that use of psychedelics might have a negative effect
on mental health for some individuals or groups, which might be
counterbalanced at a population level by a positive effect on
mental health for others. People who choose to use psychedelics
might have better initial mental health before using psychedelics,
and people who experience problems apparently related to psych-
edelics may choose to not use them again. We did not adjust for
multiple comparisons, so some of the associations with weak sta-
tistical significance are likely due to chance. Screening ques-
tions, rather than diagnostic interviews, were used as symptom
indicators. We did not have data on setting of use or factors that
might influence the experience of psychedelics. The study also
relied on self-reports of drug use. Participants’ answers to the
questions on behaviors and mental health could be influenced by
memory errors and under-reporting; however, a 14-year longitu-
dinal study reported good consistency over time in reporting of
LSD use (Johnston and O’Malley, 1997). Use of dimethyl-
tryptamine (DMT), found in the shamanic brew ayahuasca, could
not be determined from the data set; however, recent studies of
people who have used ayahuasca hundreds of times have not
detected evidence of problems (Bouso et al., 2012). Dosage and
purity of street drugs is often unknown and, in particular, sub-
stances sold as mescaline often contain LSD or other substances
(Laing and Siegel 2003). A small group (< 2%) of US adults in
prison, hospital or military service was not included in the
NSDUH sampling.
Lack of association with suicidal behavior
This study did not find any associations between psychedelic use
and increased likelihood of past year suicidal thoughts, plans or
attempts. Rather, among people with childhood depression, those
who had used psychedelics had lower likelihood of past year sui-
cidal thoughts and plans.
There is little evidence linking psychedelic use to later sui-
cide. A study of 178 adolescents with psychosis reported that sui-
cide attempt was more likely among those who had used LSD,
but there was no adjustment for other factors and it was not
recorded whether the suicide attempt occurred before or after
LSD use (Shoval et al., 2006). A case–control study of 96 adoles-
cents with depression reported that suicide attempt was more
likely among those with hallucinogen abuse or dependence, but
‘hallucinogen’ was not defined and likely included drugs such as
MDMA and PCP, there was little adjustment for other factors,
and it was not recorded whether the suicide attempt occurred
before or after hallucinogen use (Kelly et al., 2002).
In the past, some people seem to have assumed that taking
psychedelics, or indeed engaging in any introspective practice,
could lead to depression and suicide because of the supposedly
disturbing and disappointing nature of self-knowledge (Evang,
1968); however, there now seems to be greater acceptance of intro-
spective practices (such as ‘mindfulness’ or meditation) among the
public and mental health professionals. In a small number of pub-
licized cases, relatives or anti-psychedelic campaigners have
blamed an individual’s suicide on prior psychedelic use, without
evidence of any clear connection. For instance, in 1909 a Native
American peyote church member killed himself (Stewart, 1987),
and his death was then cited as evidence against peyote; in the
1960s there were a few cases where relatives blamed a suicide on
prior LSD use (Mikkelson and Mikkelson, 2005). In surveys of
US, Canadian and British physicians who administered LSD to
thousands of psychiatric patients in the 1950s, 1960s and 1970s, a
small number of suicides and suicide attempts were reported (in
people with prior suicide attempt or serious mental illness) in the
year or so after taking a dose of LSD (Canada Department of
National Health and Welfare, 1973; Cohen 1960; Malleson 1971;
US Senate, Committee on Government Operations, Subcommittee
on Executive Reorganization, 1968). Based on these and other
studies, the rate of adverse events following clinical treatment with
LSD was considered to be similar to that expected among psychi-
atric patients in general, and overall LSD was considered to
have acceptable safety for clinical use (Canada Department of
National Health and Welfare, 1973; Home Office, Department of
Health and Social Security, 1970; US Senate, Committee
on Government Operations, Subcommittee on Executive
Reorganization, 1968).
When evaluating case reports of suicide in psychedelic users,
it is important to note that suicide is one of the most common
causes of death in the general population: approximately two out
of every 100 people in the US will die by suicide (CDC, 2013).
Cases of suicide or death due to other causes during the direct
effects of psychedelics are extremely rare, despite the fact that
millions of doses are consumed annually (EMCDDA, 2011). It is
8 Journal of Psychopharmacology
of note that many of the stories from 50 years ago about death or
injury of people while on LSD appear to be unsubstantiated
urban legends (Siff, 2008).
Comments on the history of national and
international control of psychedelics
Concern about psychedelic use seems to have been based on
media sensationalism, lack of information and cultural biases,
rather than evidence-based harm assessments. As examples of
cultural biases, a 1967 case series of five university students
with ‘prolonged adverse reactions’ to peyote consisted of a
homosexual student who started a relationship with another
male student, a student with pre-existing depression who
wanted to travel to India and study Eastern religions, a student
who left school and became a ‘beatnik’, a student who was
prompted to seek psychotherapy for pre-existing social anxiety
and paranoia about homosexuals, and an engineering student
who had visions while falling asleep and eventually took a
break from school to do volunteer work (Kleber, 1967). There
was a common view in the early 20th century that mystical or
transcendent experiences were, almost by definition, delusional
and anti-scientific, and that self-exploration without the super-
vision of a trained therapist was dangerous (Evang, 1968;
Hayman, 1964). While discussing psychedelics, psychiatrist
Max Hayman wrote, ;The practices of the Christian mystics
constitute one of the most tragic chapters of human history…
Science is the path we have chosen to aid in man’s growth and
development, and mysticism in whatever guise is a contaminant
of the scientific attitude’ (Hayman, 1964). In an influential
1966 Time magazine interview, psychiatrist Sidney Cohen, one
of the most prominent critics of the emerging psychedelic cul-
ture, commented on his own LSD experience: ‘I got a massive
jolt that I’ll never forget. I got a chance to really look at myself,
and I didn’t like some of the things I saw’ (Time, 1966).
The original World Health Organization (WHO) assessment
of psychedelics, prepared for the 1971 Convention on
Psychotropic Substances, claimed that psychedelics caused a list
of problems; however, the references cited included no evidence
of harm from psilocybin, mescaline or DMT, and only a small
number of case reports and anecdotes of possibly LSD-related
adverse effects (Isbell and Chrusciel, 1970; WHO Expert
Committee on Drug Dependence, 1969). Central to the argument
for international restrictions on psychedelics was the claim that
psychedelics caused a special ‘LSD-type’ dependence, defined as
‘periodic’ use amongst ‘arty-type’ people (Eddy et al., 1965;
Isbell and Chrusciel, 1970; WHO Expert Committee on Drug
Dependence, 1969). Psychedelics were claimed to have ‘high
abuse potential’ simply because there were reports of their use
(Isbell and Chrusciel, 1970). The WHO report acknowledged that
LSD and other psychedelics ‘are usually taken in the hope of
inducing a mystical experience leading to a greater understand-
ing of the users’ personal problems and of the universe’ and that
people diagnosed with mental disorders following psychedelic
use ‘are generally believed to have been persons who were “pre-
disposed” to psychiatric disease’ (Isbell and Chrusciel, 1970).
As noted recently by the British Medical Association (BMA),
‘The cultural and social attitudes surrounding illegal drugs mean
that their classification and legal status do not directly relate to
the health risks they pose to users and communities’ (BMA,
2012). A 1970 assessment of LSD by the UK Home Office
acknowledged that use of LSD and other psychedelics was a sin-
cere spiritual practice, noting, ‘We have been content to accept
the sincerity of those of our witnesses who claimed that some
people have reached a greater awareness and insight into their
own problems and, indeed, into the meaning of life itself, through
their use of LSD’. The UK assessment explained that ‘there is a
presumption in favour of allowing adult men and women to con-
sume whatever substances they please, but this presumption must
be overridden in circumstances in which such freedom results in
a serious danger to public health… [Evidence for which] would
have to be kept under continual review in the light of rapidly
developing scientific knowledge and accelerating social change’
(Home Office, Department of Health and Social Security, 1970).
The only epidemiological data on non-clinical use of LSD
included in the UK assessment was a table showing that 127 peo-
ple who were admitted to UK psychiatric hospitals in 1966–1968
had reported having tried LSD at some point, not necessarily
related to the hospital visit (Home Office, Department of Health
and Social Security, 1970); these cases were a surely a tiny frac-
tion of total psychiatric admissions or total LSD users at that
time. We failed to find, in this study or in our previous population
study, evidence linking past year LSD use to increased likelihood
of inpatient mental health treatment (Krebs and Johansen,
2013b).
A 1975 report from the US National Institute of Mental Health
noted that people who use LSD ‘repetitively in a social pattern’
‘cannot be characterized by any specific psychiatric label’ and
called for more ‘scientific study of hallucinogen-derived mysti-
cal experiences… described as powerful and sometimes trans-
forming’ (Segal, 1975). A 1968 US Senate report on LSD policy
noted that all expert witnesses were opposed to criminalizing
LSD use and concluded: ‘The tardy reaction of the Government
was rash and excessive, resulting in the termination of almost all
research… As protector of the public safety and supporter to
medical research, the Government had an obligation to maintain
a balanced perspective concerning LSD at a time of public
tumult. It failed to do so’ (US Senate Committee on Government
Operations, Subcommittee on Executive Reorganization, 1968).
LSD, psilocybin, mescaline and several other psychedelics are
included in Schedule I of the US Controlled Substances Act of
1970; these substances were simply placed in Schedule I by
Congress without an evidence-based assessment to determine
whether LSD and other psychedelics met criteria to be added to
Schedule I. There may have been a political rather than public
health rationale behind the criminalization of psychedelic users.
It is deeply troubling to read an interview with John Ehrlichman,
advisor to US President Richard Nixon, in which he explains that
the War on Drugs was ‘really about’ hurting ‘the antiwar Left,
and black people’, and openly admits, ‘Did we know we were
lying about the drugs? Of course we did’ (Baum, 2012).
Conclusions
The results of this study are consistent with our previous popula-
tion study, early and recent randomized controlled trials, studies
of regular participants in legally recognized psychedelic religious
ceremonies, drug education materials from public agencies and
recent expert assessments of drug harms (Krebs and Johansen,
2013b). There is little evidence linking psychedelic use to lasting
Johansen and Krebs 9
mental health problems. In general, use of psychedelics does not
appear to be particularly dangerous when compared to other activ-
ities considered to have acceptable safety. It is important to take a
statistical perspective to risk, rather than focusing on case reports
and anecdotes: ‘Nothing in life is free from risk – risk is simply
impossible to avoid… Even ordinary activities – eating breakfast,
watching television, walking the dog – carry risks, however
minor’ (BMA, 2012). As Steven Pinker recently noted, ‘In a free
society, one cannot empower the government to outlaw any
behavior that offends someone just because the offendee can pull
a hypothetical future injury out of the air’ (Pinker, 2008). Overall,
it is difficult to see how prohibition of psychedelics can be justi-
fied from a public health or human rights perspective.
Acknowledgements
The Substance Abuse and Mental Health Data Archive provided the pub-
lic use data files from the National Survey on Drug Use and Health,
which was sponsored by the Office of Applied Studies of the Substance
Abuse and Mental Health Services Administration.
Declaration of Conflicting Interests
The authors declared the following potential conflicts of interest with
respect to the research, authorship, and/or publication of this article:
TSK is board leader and PØJ is a board member of EmmaSofia, a non-
profit organization based in Oslo, Norway, working to increase access to
quality-controlled MDMA and psychedelics ( www.emmasofia.org). PØJ
is also a board member of the Association for a Humane Drug Policy,
Oslo, Norway (www.fhn.no).
Funding
The authors disclosed receipt of the following financial support for the
research, authorship, and/or publication of this article:
This work was supported by the Research Council of Norway (grant
number 185924).
References
American Psychiatric Association (1994) Diagnostic and Statistical
Manual of Mental Health Disorders, 4th edn. Washington DC:
American Psychiatric Association.
Baum D (2012) Truth, lies, and audiotape. In: Smith L (ed), The Moment:
Wild, Poignant, Life-Changing Stories from 125 Writers and Artists
Famous & Obscure. New York: Harper Perennial.
Baumeister D, Barnes G, Giaroli G, et al. (2014) Classical hallucinogens
as antidepressants? A review of pharmacodynamics and putative
clinical roles. Ther Adv Psychopharmacol 4: 156–169.
BMA (2012) Risk: What’s your perspective? Available at: http://
bmaopac.hosted.exlibrisgroup.com/exlibris/aleph/a21_1/apache_
media/YIVHJTLF47Q118N114JPHDHV6RU6GP.pdf (accessed 1
November 2014).
Bogenschutz MP (2013) Studying the effects of classic hallucinogens in
the treatment of alcoholism: Rationale, methodology, and current
research with psilocybin. Curr Drug Abuse Rev 6: 17–29.
Bonson KR (2012) Hallucinogenic drugs. In: eLS. Chichester: John
Wiley & Sons. epub ahead of print DOI: 10.1002/9780470015902.
a0000166.pub2.
Bouso JC, González D, Fondevila S, et al. (2012) Personality, psy-
chopathology, life attitudes and neuropsychological performance
among ritual users of ayahuasca: A longitudinal study. PLoS ONE
7: e42421.
Bruhn JG, De Smet PA, El-Seedi HR, et al. (2002) Mescaline use for
5700 years. Lancet 359: 1866.
CAM (Coördinatiepunt Assessment en Monitoring nieuwe drugs) (2007)
Aanvullende informatie paddoincidenten in Amsterdam [Additional
information on mushroom incidents in Amsterdam]. Bilthoven: Rijk-
sinstituut voor Volksgezondheid en Milieu. Available at: www.rivm.
nl/bibliotheek/digitaaldepot/cam_paddo_aanvulling.pdf (accessed 1
November 2014).
Canada Department of National Health and Welfare (1973) Final report
of the Commission of Inquiry into the Non-Medical Use of Drugs.
Ottawa: Information Canada. p. 376.
Carhart-Harris RL and Nutt DJ (2010) User perceptions of the benefits
and harms of hallucinogenic drug use: A web-based questionnaire
study. J Subst Abuse 15: 283–300.
CDC (2013) Deaths and mortality. Available at: www.cdc.gov/nchs/
fastats/deaths.htm (accessed 1 November 2014).
CDC (2014) Emergency department visits. Available at: www.cdc.gov/
nchs/fastats/emergency-department.htm (accessed 1 November 2014).
Cohen S (1960) Lysergic acid diethylamide: Side effects and complica-
tions. J Nerv Ment Dis 130: 30–40.
Collier J (1952) The peyote cult. Science 115: 503–504.
Eddy NB, Halbach H, Isbell H, et al. (1965) Drug dependence: Its sig-
nificance and characteristics. Bull World Health Organ 32: 721–733.
EMCDDA (2011) Drug profiles: Lysergide (LSD). Available at: www.
emcdda.europa.eu/publications/drug-profiles/lsd (accessed 1 Novem-
ber 2014).
Evang K (1968) LSD: New menace to youth. UNESCO Courier, May, 18–20.
Griffiths RR, Johnson MW, Richards WA, et al. (2011) Psilocybin occa-
sioned mystical-type experiences: Immediate and persisting dose-
related effects. Psychopharmacology (Berl) 218: 649–665.
Griffiths R, Richards W, Johnson M, et al. (2008) Mystical-type experi-
ences occasioned by psilocybin mediate the attribution of personal
meaning and spiritual significance 14 months later. J Psychophar-
macol 22: 621–632.
Griffiths RR, Richards WA, McCann U, et al. (2006) Psilocybin can
occasion mystical-type experiences having substantial and sustained
personal meaning and spiritual significance. Psychopharmacology
(Berl) 187: 268–283.
Halberstadt AL (2015) Recent advances in the neuropsychopharmacol-
ogy of serotonergic hallucinogens. Behav Brain Res 277: 99–120.
Hallock RM, Dean A, Knecht ZA, et al (2013) A survey of hallucino-
genic mushroom use, factors related to usage, and perceptions of use
among college students. Drug Alcohol Depend 130: 245–248.
Halpern JH, Sherwood AR, Hudson JI, et al. (2005) Psychological and
cognitive effects of long-term peyote use among Native Americans.
Biol Psychiatry 58: 624–631.
Hayman M (1964) Science, mysticism and psychopharmacology. Calif
Med 101: 266–271.
Hendricks PS, Clark CB, Johnson MW, et al (2014) Hallucinogen use pre-
dicts reduced recidivism among substance-involved offenders under
community corrections supervision. J Psychopharmacol 28: 62–66.
Home Office, Department of Health and Social Security (1970) The amphet-
amines and lysergic acid diethylamide (LSD). Report by the Advisory
Committee on Drug Dependence. London: Her Majesty’s Stationery
Office.
Isbell H and Chrusciel TL (1970) Dependence liability of ‘non-narcotic’
drugs. Bull World Health Organ 43 (Suppl): 5–111.
Johnson M, Richards W and Griffiths R (2008) Human hallucinogen
research: Guidelines for safety. J Psychopharmacol 22: 603–620.
Johnson MW, Garcia-Romeu A, Cosimano MP, et al. (2014) Pilot study
of the 5-HT2AR agonist psilocybin in the treatment of tobacco
addiction. J Psychopharmacol 28: 983–992.
Johnston LD and O’Malley PM (1997) The recanting of earlier reported
drug use by young adults. NIDA Res Monogr 167: 59–80.
Kelly TM, Cornelius JR and Lynch KG (2002) Psychiatric and substance
use disorders as risk factors for attempted suicide among adoles-
cents: A case control study. Suicide Life Threat Behav 32: 301–312.
10 Journal of Psychopharmacology
Kessler RC, Barker PR, Colpe LJ, et al. (2003a) Screening for serious men-
tal illness in the general population. Arch Gen Psychiatry 60: 184–189.
Kessler RC, Berglund P, Demler O, et al. (2003b) The epidemiology of
major depressive disorder: Results from the National Comorbidity
Survey Replication (NCS-R). JAMA 289: 3095–3105.
Kessler RC, Green JG, Gruber MJ, et al. (2010) Screening for serious
mental illness in the general population with the K6 screening scale:
Results from the WHO World Mental Health (WMH) survey initia-
tive. Int J Methods Psychiatr Res 19 (Suppl 1): 4–22.
Kleber HD (1967) Prolonged adverse reactions from unsupervised use of
hallucinogenic drugs. J Nerv Ment Dis 144: 308–319.
Krebs TS and Johansen PØ (2012) Lysergic acid diethylamide (LSD) for
alcoholism: Meta-analysis of randomized controlled trials. J Psycho-
pharmacol 26: 994–1002.
Krebs TS and Johansen PØ (2013a) Over 30 million psychedelic users in
the United States. F1000Res 2: 98. .
Krebs TS and Johansen PØ (2013b) Psychedelics and mental health: A
population study. PLoS ONE 8: e63972.
La Barre W, McAllester DP, Slotkin JS, et al. (1951) Statement on pey-
ote. Science 114: 582–583.
Laing R and Siegel JA (eds) (2003) Hallucinogens: A Forensic Drug
Handbook. Waltham, MA: Academic Press.
Le Farge O (1960) Defining peyote as a narcotic. Am Anthropologist 62:
687–689.
McGlothlin WH and Arnold DO (1971) LSD revisited. A ten-year fol-
low-up of medical LSD use. Arch Gen Psychiatry 24: 35–49.
MacLean KA, Johnson MW and Griffiths RR (2011) Mystical experiences
occasioned by the hallucinogen psilocybin lead to increases in the per-
sonality domain of openness. J Psychopharmacol 25: 1453–1461.
McWilliams SA and Tuttle RJ (1973) Long-term psychological effects of
LSD. Psychol Bull 79: 341–351.
Malleson N (1971) Acute adverse reactions to LSD in clinical and experi-
mental use in the United Kingdom. Br J Psychiatry 118: 229–230.
Mikkelson B and Mikkelson DP (2005) Death of Diane Linkletter. Urban
Legends Reference Pages. Available at: www.snopes.com/horrors/
drugs/linkletter.asp (accessed 1 November 2014).
Morgan CJ, Muetzelfeldt L, Muetzelfeldt M, et al. (2010) Harms asso-
ciated with psychoactive substances: Findings of the UK National
Drug Survey. J Psychopharmacol 24: 147–153.
Newberne RE and Burke CH (1922) Peyote: An Abridged Compilation
from the Files of the Bureau of Indian Affairs. Washington DC: US
Government Printing Office. Available at: http://archive.org/details/
peyoteabridgedco00unit (accessed 1 November 2014).
Nutt DJ, King LA and Nichols DE (2013) Effects of Schedule I drug laws
on neuroscience research and treatment innovation. Nat Rev Neuro-
sci 14: 577–585.
Nutt DJ, King LA, Phillips LD; Independent Scientific Committee on
Drugs (2010) Drug harms in the UK: A multicriteria decision analy-
sis. Lancet 376: 1558–1565.
Nutt D, King LA, Saulsbury W, et al. (2007) Development of a rational scale
to assess the harm of drugs of potential misuse. Lancet 369: 1047–1053.
Pinker S (2008) The stupidity of dignity. New Republic 28 May 2008.
Available at: http://pinker.wjh.harvard.edu/articles/media/The%20
Stupidity%20of%20Dignity.htm (accessed 1 November 2014).
Schankin CJ, Maniyar FH, Digre KB, et al. (2014) ‘Visual snow’ – a
disorder distinct from persistent migraine aura. Brain 137: 1419–
1428.
Segal J (ed) (1975) Research in the service of mental health. Report of
the Research Task Force of the National Institute of Mental Health.
Washington, DC: US Government Printing Office.
Shoval G, Sever J, Sher L, et al. (2006) Substance use, suicidality, and
adolescent-onset schizophrenia: An Israeli 10-year retrospective
study. J Child Adolesc Psychopharmacol 16: 767–775.
Siff SI (2008) Glossy visions: Coverage of LSD in popular magazines,
1954–1968 (electronic thesis or dissertation). Available online
at: http://etd.ohiolink.edu/ap/10?0::NO:10:P10_ACCESSION_
NUM:ohiou1225818399 (accessed November 1 2014).
Stewart OC (1987) Peyote Religion: A History. Norman, OK: University
of Oklahoma Press, p. 168.
Studerus E, Kometer M, Hasler F, et al. (2011) Acute, subacute and
long-term subjective effects of psilocybin in healthy humans: A
pooled analysis of experimental studies. J Psychopharmacol 25:
1434–1452.
Taylor M, Mackay K, Murphy J, et al. (2012) Quantifying the RR of
harm to self and others from substance misuse: Results from a sur-
vey of clinical experts across Scotland. BMJ Open 2. DOI: 10.1136/
bmjopen-2011-000774.
Time (1966) An epidemic of acid heads. Time, 11 March 1966, p.56.
United Nations General Assembly (1948) Universal declaration of
human rights. Available at: www.refworld.org/docid/3ae6b3712c.
html (accessed 1 November 2014).
US Department of Health and Human Services, Substance Abuse and
Mental Health Services Administration, Center for Behavioral
Health Statistics and Quality (2013) Drug Abuse Warning Network
(DAWN), 2010. ICPSR34083-v2. Report, Ann Arbor, MI: Inter-
University Consortium for Political and Social Research.
US Senate, Committee on Government Operations, Subcommittee on
Executive Reorganization (1968) Organization and Coordination of
Federal Drug Research and Regulatory Programs: LSD. Washing-
ton, DC: US Government Printing Office. p. 7.
van Amsterdam J, Opperhuizen A, Koeter M, van den Brink W
(2010) Ranking the harm of alcohol, tobacco and illicit drugs for
the individual and the population. Eur Addict Res 16: 202–7. doi:
10.1159/000317249.
van Amsterdam J, Opperhuizen A, Koeter M, et al. (2010) Ranking the
harm of alcohol, tobacco and illicit drugs for the individual and the
population. Eur Addict Res 16: 202–207.
Vittinghoff E and McCulloch CE (2007) Relaxing the rule of ten events
per variable in logistic and Cox regression. Am J Epidemiol 165:
710–718.
Walsh C (2014). Beyond religious freedom: Psychedelics and cognitive
liberty. In: Labate BC and Cavnar C (eds) Prohibition, Religious
Freedom, and Human Rights: Regulating Traditional Drug Use.
Berlin: Springer, pp. 211–233.
WHO Expert Committee on Drug Dependence (1969) Sixteenth report.
Technical Report Series 407. Vienna: United Nations. Available
at: http://whqlibdoc.who.int/trs/WHO_TRS_407.pdf (accessed 1
November 2014).
... Als weitere schwere Nebenwirkung von Halluzinogenen gilt die Auslösung einer psychotischen Erkrankung. Während einige Autoren keinen Zusammenhang zwischen dem Konsum dieser Substanzen und psychotischen Störungen sehen (39), berichten andere, dass einige Personen dafür anfällig sein könnten (40). In einer Übersichtsarbeit aus dem Jahr 1996 wurden bei Halluzinogenkonsumenten Häufigkeiten von 0,08 bis 4,6% mit einer Tendenz zu höheren Raten bei psychiatrischen Patienten festgestellt. ...
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Die Alkoholabhängigkeit ist eine häufige psychische Erkrankung mit erheblichen Auswirkungen auf die Betroffenen und deren Umfeld. Die aktuellen Behandlungsansätze sind wirksam, allerdings spricht ein erheblicher Teil der Patienten nur sehr unzureichend auf etablierte Therapien an. In den 1950er- und 1960er-Jahren wurden Halluzinogene, insbesondere LSD (Lysergsäurediethylamid), in der Behandlung von Patienten mit Alkoholabhängigkeit in zahlreichen Studien untersucht. Jedoch blieb bis zum Ende dieses Forschungszweigs in den 1960er-Jahren die Effektivität dieses Ansatzes aufgrund von methodischen Aspekten umstritten. Zurzeit werden mit dem verwandten Wirkstoff Psilocybin mehrere Studien durchgeführt, die viele methodische Mängel der ersten Studien nicht aufweisen. Innerhalb der nächsten Jahre sollten diese Projekte wissenschaftlich fundiertere Informationen über das Potenzial von Halluzinogenen in der Behandlung der Alkoholabhängigkeit erbringen.
... Moreover, enduring increases in well-being are reported in nonclinical populations in research settings (Griffiths et al., 2006 and with naturalistic classic psychedelic use (Forstmann et al., 2020;Agin-Liebes et al., 2021;Mans et al., 2021). Population-level analyses also suggest that classic psychedelic use is associated with protective mental health effects (Hendricks et al., 2015a(Hendricks et al., , 2015bJohansen and Krebs, 2015;Pisano et al., 2017). On a more biologic level, in vivo and in vitro studies have revealed that classic psychedelics produce significant increases in neuroplasticity and have potent anti-inflammatory effects (Flanagan and Nichols, 2018;Inserra et al., 2021a), which suggests therapeutic potential for a range of conditions. ...
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The extremes of human experiences, such as those occasioned by classic psychedelics and psychosis, provide a rich contrast for understanding how components of these experiences impact well-being. In recent years, research has suggested that classic psychedelics display the potential to promote positive enduring psychologic and behavioral changes in clinical and nonclinical populations. Paradoxically, classic psychedelics have been described as psychotomimetics. This review offers a putative solution to this paradox by providing a theory of how classic psychedelics often facilitate persistent increases in well-being, whereas psychosis leads down a "darker" path. This will be done by providing an overview of the overlap between the states (i.e., entropic processing) and their core differences (i.e., self-focus). In brief, entropic processing can be defined as an enhanced overall attentional scope and decreased predictability in processing stimuli facilitating a hyperassociative style of thinking. However, the outcomes of entropic states vary depending on level of self-focus, or the degree to which the associations and information being processed are evaluated in a self-referential manner. We also describe potential points of overlap with less extreme experiences, such as creative thinking and positive emotion-induction. Self-entropic broadening theory offers a heuristically valuable perspective on classic psychedelics and their lasting effects and relation to other states by creating a novel synthesis of contemporary theories in psychology. SIGNIFICANCE STATEMENT: Self-entropic broadening theory provides a novel theory examining the psychedelic-psychotomimetic paradox, or how classic psychedelics can be therapeutic, yet mimic symptoms of psychosis. It also posits a framework for understanding the transdiagnostic applicability of classic psychedelics. We hope this model invigorates the field to provide more rigorous comparisons between classic psychedelic-induced states and psychosis and further examinations of how classic psychedelics facilitate long-term change. As a more psychedelic future of psychiatry appears imminent, a model that addresses these long-standing questions is crucial.
... Although more is known about the general impact and prevalence of negative attitudes and stigma toward drugs among mental health professionals, relatively little is known about stigma toward psychedelics specifically. We are aware of only one prior survey on mental health professional's attitudes toward psychedelics which found that among a sample of 324 U.S. psychiatrists (Barnett et al., 2018), the majority thought psychedelics increased the risk of subsequent psychiatric problems despite population studies showing no significant association between psychedelics and some studies even associating lifetime psychedelic use with lower rates of mental health difficulties (Carhart-Harris & Nutt 2010;Johansen & Krebs 2015). Additionally, a significant minority thought that psychedelic use was unsafe even under medical supervision even though there have been few observed serious adverse events in clinical trials (dos Santos et al., 2018;Studerus et al., 2011). ...
Article
As evidence for psychedelic-assisted therapy accumulates, legalization becomes more likely. As a result, there is an increasing need for psychologists to become educated about psychedelics and their therapeutic effects as they will play an important role in disseminating this treatment. Therefore, understanding psychologists’ current attitudes toward psychedelics is integral in informing dissemination and implementation efforts. In this article, we examined associations between individual difference variables and psychologists’ attitudes toward psychedelics, including age, gender, region, religious affiliation, personal experience with psychedelics, friends’ or loved ones’ experiences with psychedelics, level of training in addiction treatment, and knowledge of psychedelics. Results indicated that participants who were men, lived in West or Northeast regions of the USA, were younger, had greater knowledge of risks and benefits of psychedelics, were religiously unaffiliated, or had direct or indirect (i.e. through peers) experience with psychedelics reported more positive attitudes toward psychedelics. The only variable not associated with more positive attitudes was previous addictions treatment training. These findings suggest that psychologists are not monolithic in their attitudes toward psychedelics. Furthermore, these findings can help inform potential paths for improving attitudes toward psychedelics among psychologists, such as by emphasizing the importance of using case studies in public education efforts.
... A number of randomised controlled trials have now been performed, with one direct SSRI comparator trial finding psychedelic therapy to compare very favourably in multiple domains (Carhart-Harris et al., 2021a). Population studies, indirectly examining the effects of psychedelic-use, have found lower suicide and mental disorders rates in 'recent' psychedelic users versus a matched sample (Hendricks et al., 2015;Johansen and Krebs, 2015;Simonsson et al., 2021). ...
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Background Over the last two decades, a number of studies have highlighted the potential of psychedelic therapy. However, questions remain to what extend these results translate to naturalistic samples, and how contextual factors and the acute psychedelic experience relate to improvements in affective symptoms following psychedelic experiences outside labs/clinics. The present study sought to address this knowledge gap. Aim Here, we aimed to investigate changes in anxiety and depression scores before versus after psychedelic experiences in naturalistic contexts, and how various pharmacological, extrapharmacological and experience factors related to outcomes. Method Individuals who planned to undergo a psychedelic experience were enrolled in this online survey study. Depressive symptoms were assessed at baseline and 2 and 4 weeks post-psychedelic experience, with self-rated Quick Inventory of Depressive Symptomatology (QIDS-SR-16) as the primary outcome. To facilitate clinical translation, only participants with depressive symptoms at baseline were included. Sample sizes for the four time points were N = 302, N = 182, N = 155 and N = 109, respectively. Results Relative to baseline, reductions in depressive symptoms were observed at 2 and 4 weeks. A medicinal motive, previous psychedelic use, drug dose and the type of acute psychedelic experience (i.e. specifically, having an emotional breakthrough) were all significantly associated with changes in self-rated QIDS-SR-16. Conclusion These results lend support to therapeutic potential of psychedelics and highlight the influence of pharmacological and non-pharmacological factors in determining response. Mindful of a potential sample and attrition bias, further controlled and observational longitudinal studies are needed to test the replicability of these findings.
... This suggests that recreational users are attempting to benefit from the therapeutic effects of psychedelics observed in clinical studies in recreational settings and applying them to a wide range of untested issues. There is some [9], but not consistent [10] evidence that past-year use of psychedelics is associated with depression and suicidal thinking, and although the direction of this relationship is unknown, this finding may support the view that individuals suffering from these conditions are drawn towards trying psychedelics in an attempt to self-treat. ...
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Background Alongside a recent revival in the use of psychedelics in clinical settings, there have been increases in the prevalence of recreational use, with many using psychedelics to deal with difficult emotions or to improve well-being. While clinical research is conducted in carefully controlled settings, this is not necessarily the case for recreational use. In this mixed methods online survey study, we aimed to develop an understanding of frequently used psychedelic harm reduction practices in recreational settings and how their use relates to the psychedelic experience. We also aimed to characterise users’ first and most recent psychedelic trips to understand how harm reduction changes with experience. Methods Participants ( n = 163) recounted their first and most recent psychedelic experience by providing details about the harm reduction practices they employed and completing the Challenging Experience Questionnaire (CEQ) and Emotional Breakthrough Inventory (EBI). We also asked open-ended questions for a more in-depth qualitative understanding of their views on psychedelic harm reduction. Results Using ANOVA, we observe greater use of harm reduction practices for participants’ most recent versus first psychedelic experience and that use of these practices is positively associated with EBI scores and negatively associated with CEQ scores (particularly for the first experience). Participants engaged in a wide range of harm reduction practices and we provide details of those which are most commonly used and those which are deemed most important by experienced users. Our qualitative analysis indicated that participants were largely positive about psychedelics and many recounted profound positive experiences. While specifics of the drug they were taking was important for aspects of harm reduction, participants largely focused on the importance of ensuring a good “set and setting” for enhancing positive effects. Conclusions Our research helps us understand how engagement in harm reduction may increase with experience. Our mixed methods data shed light on the perceived importance of different harm reduction practices and examine their association with the psychedelic experience itself. Together, our research has important implications for the development of psychedelic harm reduction advice and provides opportunities for future research to explore the importance of these different practices in more detail.
... However, in 2015, a study has found that those who used a classic psychedelic [i.e., psilocybin, N,Ndimethyltryptamine, lysergic acid diethylamide (LSD), and mescaline] in the past year had a reduced risk of attempted suicide by 36% (Hendricks et al., 2015). Also, in contrast to popular belief that using classic psychedelics, including psilocybin, can increase the risk of psychiatric illnesses, such as schizophrenia (Quednow et al., 2010), psilocybin is found to be unrelated to mental health problems (Johansen and Krebs, 2015). ...
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Classical psychedelics represent a family of psychoactive substances with structural similarities to serotonin and affinity for serotonin receptors. A growing number of studies have found that psychedelics can be effective in treating various psychiatric conditions, including post-traumatic stress disorder, major depressive disorder, anxiety, and substance use disorders. Mental health disorders are extremely prevalent in the general population constituting a major problem for the public health. There are a wide variety of interventions for mental health disorders, including pharmacological therapies and psychotherapies, however, treatment resistance still remains a particular challenge in this field, and relapse rates are also quite high. In recent years, psychedelics have become one of the promising new tools for the treatment of mental health disorders. In this review, we will discuss the three classic serotonergic naturally occurring psychedelics, psilocybin, ibogaine, and N, N-dimethyltryptamine, focusing on their pharmacological properties and clinical potential. The purpose of this article is to provide a focused review of the most relevant research into the therapeutic potential of these substances and their possible integration as alternative or adjuvant options to existing pharmacological and psychological therapies.
... Classic psychedelics have the lowest physiological toxicities of all well-known "drugs of abuse" (Gable, 2004). A recent populationbased study of 135,095 randomly selected US adults, including 19,299 users of psychedelics (Johansen and Krebs, 2015) found no significant associations between lifetime use of classic psychedelics and past-year incidence of serious psychological distress, mental health treatment, depression, anxiety, or suicidal ideation or suicide attempts. Despite their schedule I status, classic psychedelics do not reliably lead to selfadministration behavior in laboratory animals. ...
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Post-traumatic stress disorder (PTSD), a common condition with potentially devastating individual, family, and societal consequences, is highly associated with substance use disorders (SUDs). The association between PTSD and SUD is complex and may involve adverse childhood experiences (ACEs), historical and multi-generational traumas, and social determinants of health as well as cultural and spiritual contexts. Current psychosocial and pharmacological treatments for PTSD are only modestly effective, and there is a need for more research on therapeutic interventions for co-occurring PTSD and SUD, including whether to provide integrated or sequential treatments. There is a current resurgence of interest in psychedelics as potential treatment augmentation for PTSD and SUDs with an appreciation of the risks in this target population. This paper reviews the historical perspective of psychedelic research and practices, as well as the intersection of historical trauma, ACEs, PTSD, and SUDs through the lens of New Mexico. New Mexico is a state with high populations of Indigenous and Hispanic peoples as well as high rates of trauma, PTSD, and SUDs. Researchers in New Mexico have been leaders in psychedelic research. Future directions for psychedelic researchers to consider are discussed, including the importance of community-based participatory approaches that are more inclusive and respectful of Indigenous and other minority communities.
... Future trials should explore which whether SSRIs, the most common PTSD pharmacotherapy, and other concomitant medications are safe and appropriate to continue during psilocybin-therapy. Regarding risk of self-directed violence, two large population studies reported psilocybin use is associated with reduced SI, planning, and attempt (Johansen and Krebs 2015;Krebs and Johansen 2013). This same pattern of findings was also found in a longitudinal study of women sex workers with high trauma exposure (Argento et al. 2017). ...
Chapter
Posttraumatic stress disorder (PTSD) is a debilitating, chronic disorder and efficacy rates of current PTSD treatments are underwhelming. There is a critical need for innovative approaches. We provide an overview of trauma and PTSD and cite literature providing converging evidence of the therapeutic potential of psilocybin for PTSD. No study to date has investigated psilocybin or psilocybin-assisted psychotherapy (PAP) as treatments for PTSD. An open-label study in traumatized AIDS survivors found that PAP reduced PTSD symptoms, attachment anxiety, and demoralization. Several PAP trials show preliminary efficacy in facilitating confronting traumatic memories, decreasing emotional avoidance, depression, anxiety, pessimism, and disconnection from others, and increasing acceptance, self-compassion, and forgiveness of abusers, all of which are relevant to PTSD recovery. There is also early evidence that other classic psychedelics may produce large reductions in PTSD symptoms in combat veterans. However, this body of literature is small, mechanisms are not yet well understood, and the risks of using psychedelic compounds for trauma-related disorders need further study. In sum, evidence supports further investigation of PAP as a radically new approach for treating PTSD.
Article
To date, the clinical and scientific literature has best documented the effects of classical psychedelics, such as lysergic acid diethylamide (LSD), psilocybin, and dimethyltryptamine (DMT), in typical quantities most often associated with macrodosing. More recently, however, microdosing with psychedelics has emerged as a social trend and nascent therapeutic intervention. This variation in psychedelic practice refers to repeat, intermittent ingestion of less-than-macrodose amounts that do not cause the effects associated with full-blown “trips”. Microdosing paves the road to incorporating psychedelic drugs into a daily routine while maintaining, or even improving, cognitive and mental function. Unlike macrodosing with psychedelics, the influence of microdosing remains mostly unexplored. And yet, despite the paucity of formal studies, many informal accounts propose that microdosing plays an important role as both a therapeutic intervention (e.g., in mental disorders) and enhancement tool (e.g., recreationally—to boost creativity, improve cognition, and drive personal growth). In response to this relatively new practice, we provide an integrative synthesis of the clinical, social, and cultural dimensions of microdosing. We describe some of the overarching context that explains why this practice is increasingly in vogue, unpack potential benefits and risks, and comment on sociocultural implications. In addition, this article considers the effects that macro- and microdoses have on behavior and psychopathology in light of their dosage characteristics and contexts of use.
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Proper assessment of the harms caused by the misuse of drugs can inform policy makers in health, policing, and social care. We aimed to apply multicriteria decision analysis (MCDA) modelling to a range of drug harms in the UK. Method Members of the Independent Scientific Committee on Drugs, including two invited specialists, met in a 1-day interactive workshop to score 20 drugs on 16 criteria: nine related to the harms that a drug produces in the individual and seven to the harms to others. Drugs were scored out of 100 points, and the criteria were weighted to indicate their relative importance. Findings MCDA modelling showed that heroin, crack cocaine, and metamfetamine were the most harmful drugs to individuals (part scores 34, 37, and 32, respectively), whereas alcohol, heroin, and crack cocaine were the most harmful to others (46, 21, and 17, respectively). Overall, alcohol was the most harmful drug (overall harm score 72), with heroin (55) and crack cocaine (54) in second and third places. Interpretation These findings lend support to previous work assessing drug harms, and show how the improved scoring and weighting approach of MCDA increases the differentiation between the most and least harmful drugs. However, the findings correlate poorly with present UK drug classification, which is not based simply on considerations of harm.
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Despite suggestive early findings on the therapeutic use of hallucinogens in the treatment of substance use disorders, rigorous follow-up has not been conducted. To determine the safety and feasibility of psilocybin as an adjunct to tobacco smoking cessation treatment we conducted an open-label pilot study administering moderate (20 mg/70 kg) and high (30 mg/70 kg) doses of psilocybin within a structured 15-week smoking cessation treatment protocol. Participants were 15 psychiatrically healthy nicotine-dependent smokers (10 males; mean age of 51 years), with a mean of six previous lifetime quit attempts, and smoking a mean of 19 cigarettes per day for a mean of 31 years at intake. Biomarkers assessing smoking status, and self-report measures of smoking behavior demonstrated that 12 of 15 participants (80%) showed seven-day point prevalence abstinence at 6-month follow-up. The observed smoking cessation rate substantially exceeds rates commonly reported for other behavioral and/or pharmacological therapies (typically <35%). Although the open-label design does not allow for definitive conclusions regarding the efficacy of psilocybin, these findings suggest psilocybin may be a potentially efficacious adjunct to current smoking cessation treatment models. The present study illustrates a framework for future research on the efficacy and mechanisms of hallucinogen-facilitated treatment of addiction.
Chapter
This chapter will examine the blurred boundaries between the sacred and the secular when it comes to psychedelic experiences, and the inevitable ensuing arbitrariness involved in protecting some such rituals and not others. It will put forth the argument that there is a need to move beyond simply seeking exemptions from drug prohibition in the name of religious freedom; rather, there should be a broader right to ingest psychedelics as an aspect of cognitive liberty. Cognitive liberty is the right to control one's own consciousness. It is a concept that equates to freedom of thought, a right protected internationally by the Universal Declaration of Human Rights and enforceable in Europe through Article 9 of the European Convention of Human Rights. © Springer-Verlag Berlin Heidelberg 2014. All rights are reserved.
Article
A follow-up survey of 247 persons who received d-lysergic acid diethylamide (LSD) in either an experimental (nonmedical) or Psychotherapeutic setting was made to determine the lasting effects, if any, related to use of the drug. Information was collected from each by a structured interview and self-administered questionnaire. Some subsequent nonmedical use of LSD was reported by 23%, who attributed more personality changes to the drug's use. There is, however, little evidence that measurable, lasting personality, belief, value, attitude, or behavior changes were produced in the sample as a whole. Compulsive patterns of LSD use rarely developed; the nature of the drug effect apparently is such that it becomes less attractive with continued use and, in the long-term, is almost always self-limiting.
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Serotonergic hallucinogens, such as (+)-lysergic acid diethylamide, psilocybin, and mescaline, are somewhat enigmatic substances. Although these drugs are derived from multiple chemical families, they all produce remarkably similar effects in animals and humans, and they show cross-tolerance. This article reviews the evidence demonstrating the serotonin 5-HT2A receptor is the primary site of hallucinogen action. The 5-HT2A receptor is responsible for mediating the effects of hallucinogens in human subjects, as well as in animal behavioral paradigms such as drug discrimination, head twitch response, prepulse inhibition of startle, exploratory behavior, and interval timing. Many recent clinical trials have yielded important new findings regarding the psychopharmacology of these substances. Furthermore, the use of modern imaging and electrophysiological techniques is beginning to help unravel how hallucinogens work in the brain. Evidence is also emerging that hallucinogens may possess therapeutic efficacy.