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An Evidence Based Review of Acute and Long-Term Effects of
Cannabis Use on Executive Cognitive Functions
Rebecca D. Crean, Ph.D.1, Natania A. Crane, B.A.1, and Barbara J. Mason, Ph.D.1,✉
1 Committee on the Neurobiology of Addictive Disorders; The Scripps Research Institute; La
Jolla, CA, 92037, USA
Abstract
Cannabis use has been shown to impair cognitive functions on a number of levels—from basic
motor coordination to more complex executive function tasks, such as the ability to plan, organize,
solve problems, make decisions, remember, and control emotions and behavior. These deficits
differ in severity depending on the quantity, recency, age of onset and duration of marijuana use.
Understanding how cannabis use impairs executive function is important. Individuals with
cannabis-related impairment in executive functions have been found to have trouble learning and
applying the skills required for successful recovery, putting them at increased risk for relapse to
cannabis use. Here we review the research on the acute, residual, and long-term effects of cannabis
use on executive functions, and discuss the implications for treatment.
Keywords
cannabis; marijuana; cognition; executive functions; treatment
OVERVIEW
Consumption of cannabis for medical purposes is legal with a prescription in 15 states, and
many states are in the process of decriminalizing non-medical marijuana use. More than
97.5 million Americans over the age of 12 have used illicit marijuana, and it is considered
by many to be a benign recreational drug. However, evidence exists of significant harm for
some individuals, with 1 in 10 users developing cannabis dependence (SAMHSA, 2007).
Furthermore, sixteen percent (~300,000) of all substance abuse treatment admissions in the
United States were for cannabis-related disorders; this is second only to alcohol-related
disorders (SAMHSA, 2006). It is estimated that more than 4 million Americans meet
Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV; APA, 1994) diagnostic
criteria for cannabis dependence (SAMHSA, 2007). This figure has doubled from 2001, and
will likely continue to grow. Thus, an understanding of the effects of cannabis on executive
functions is likely to be of widespread clinical relevance.
Delta 9-tetrahydrocannabinol (THC) is the primary psychoactive constituent of the cannabis
sativa plant and is believed to be primarily responsible for the cognitive effects and the
addictive potential of smoked cannabis. THC intoxication has been shown to impair
cognitive function on a number of levels—from basic motor coordination to more complex
Address correspondence to: Dr. Barbara J. Mason, Committee on the Neurobiology of Addictive Disorders, 10550 North Torrey Pines
Road, TPC-5; The Scripps Research Institute, La Jolla, CA 92037; USA; Phone: +1.858.784.7324; Fax: +1.858.784.7340;
mason@scripps.edu.
The authors have no relevant financial interests to disclose.
NIH Public Access
Author Manuscript
J Addict Med. Author manuscript; available in PMC 2012 March 1.
Published in final edited form as:
J Addict Med
. 2011 March 1; 5(1): 1–8. doi:10.1097/ADM.0b013e31820c23fa.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
tasks, such as the ability to plan, organize, solve problems, make decisions, remember, and
control emotions and behavior. The higher level cognitive functions, termed executive
functions (see Table 1), are critically important, particularly when dealing with novel
situations in which decisions must be made. This array of higher cognitive functions are
vital for overriding and inhibiting responses that otherwise would be automatic or require
little thought, such as continued substance abuse (Luria, 2002).
Some cannabis-related executive function deficits improve after cessation of cannabis use
(Pope et al., 2002), but growing evidence suggests that other deficits persist after cannabis is
discontinued (Bolla et al., 2005), and may hinder an individual’s ability to make the best use
of behavioral therapies and put him or her at greater risk for relapse to cannabis use
(Aharonovich et al., 2008; Blume and Marlatt, 2009). Adding to the complexity of this issue
is the fact that many factors can impact cannabis-related impairment and recovery of
executive functions, including age of onset of smoking cannabis, years of use, and amount
of regular use (Grant et al., 2003). This clinical conundrum is compounded by the fact that
treatment professionals may not be able to easily identify patients with cannabis-related
impairment in executive functions without the benefit of neuropsychological assessment
(Fals-Stewart, 1997).
Although there is convincing evidence that acute cannabis use generally affects cognitive
and motor functions, it is less clear as to whether those deficits are short term and transient
or if they are more enduring. Previously published reports (Pope et al., 2001; 2002) using
traditional neuropsychological assessment methods typically show a resolution of deficits by
28 days of abstinence. However, as neuroimaging technology has improved, more recent
reports show subtle, long-term effects of cannabis on cognition and brain functioning (Bolla
et al., 2005). In addition, newly published reports suggest that the deficits change as a
function of the quantity of cannabis consumed and duration of use (Solowij et al., 1995;
2002; Grant et al., 2003). Adolescents who started smoking between the ages of 14–22 years
old and stopped by age 22 had significantly more cognitive problems at age 27 than their
non-using peers (Brook et al., 2008). In addition, adult cannabis users who began smoking
before the age of 17, but not users who began smoking after the age of 17, had significant
impairments in measures of executive functioning, including abstract reasoning, verbal
fluency, and verbal learning and memory compared to non-using controls (Pope et al.,
2003).
Understanding how cannabis use impacts executive functions is important for clinicians.
Patients who routinely use cannabis may have deficits that make it difficult for them to
adhere to treatment, to follow medical advice, and to experience successful outcomes.
Literature Search Criteria
A literature search was conducted through Medline and PsychInfo with no publication date
restrictions. The search terms used were “marijuana”, “delta-9-tetra-hydrocannabinol,”
“THC,” and “cannabis” crossed with “neuro,” “cognitive,” “assessment,”
“neuropsychological,” “brain functioning,” “executive functions,” “impairment” or
“clinical.” Articles containing these search terms were included in this evidence-based
review if they reported results of cannabis-related studies conducted in an adult, human
population and utilized neuropsychological assessments to assess executive functions.
Review papers, commentaries, pre-clinical studies and those involving human children and
adolescents were excluded.
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ACUTE EFFECTS OF CANNABIS ON EXECUTIVE FUNCTIONS (0 to 6 hours
after use)
Smoking cannabis produces levels of THC in blood plasma that can be detected almost
immediately and which reach peak concentrations within minutes (Grotenhermen, 2003).
THC is fat soluble and, therefore, easily stored and released into the bloodstream
(Grotenhermen, 2003). Because it is fat soluble, THC has a long half-life and can be
detected in urine anywhere from one day to more than a month after ingestion (Huestis et
al., 1996). The psychoactive effects of cannabis are experienced immediately after smoking,
with peak levels of intoxication occurring after approximately 30 minutes and lasting several
hours (Grotenhermen, 2003).
Researchers first began studying the acute effects of cannabis on neuropsychological
functioning in the 1970’s and consistently found disruptions in learning and memory
functions (Ferraro, 1980). The findings on executive functioning, however, have been less
clear (Pope et al., 1995). For the purposes of this review, literature reviewed for the acute
effects of cannabis on executive functions are studies in which assessment took place
between immediately upon smoking cannabis and up to six hours since last use. The
findings are detailed below.
Attention and Concentration
Attentional processing is the ability to use both divided and sustained attention when
targeting a stimulus and it is mediated by the frontal lobes (Grady, 1999). Several
investigators studied the acute effects of cannabis specifically on attentional processing.
Hart et al. (2001) studied the effects of placebo, light (1.8%), and heavy (3.9%) THC
cigarettes in chronic, daily cannabis users and found no significant differences in the
accuracy of response to attentional tasks. However, performance on a tracking task, which
requires sustained attention, was found to improve significantly after the high dose of THC,
relative to the other conditions. Similarly, Haney et al. (1999) found that after acute
intoxication, daily cannabis users significantly improved on a task of divided attention.
Morrison et al. (2009) tested light cannabis users 30 minutes after administration of either
placebo or moderate (2.5%) THC cigarettes and found significant impairment in attention
and concentration in the THC group compared with the placebo group. These discrepant
findings may be explained by the characteristics of the subjects studied; Haney et al. (1999)
and Hart et al. (2001) studied chronic, daily cannabis smokers, whereas the subjects used in
Morrison et al. (2009) were infrequent cannabis users. Hence, the disparate findings may be
a function of sample differences involving degree of cannabis exposure and the degree of
tolerance and other neuroadaptions resulting from long-term cannabis use.
Information processing is a fundamental aspect of attention and concentration and a basic
building block of higher order cognitive processing. (Dosher and Sperling, 1998). Kelleher
et al. (2004) evaluated information processing in heavy, chronic cannabis users compared
with non-cannabis using controls. Cannabis users completed a task when abstinent and then
attempted the same task 30 minutes after smoking their “regular” amount of cannabis. They
found that users in the abstinent state showed significantly slowed information processing
speed compared with controls; however, functioning normalized after smoking cannabis.
According to the authors, this finding shows that abstinence following chronic cannabis use
may result in a deficit in information processing, which normalizes after acute intoxication.
They surmised that cannabis users who experience slowing of information processing as a
result of abstinence following chronic cannabis use may be at risk to resume smoking in an
attempt to regain information processing abilities.
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Decision-Making and Risk-Taking
Decision-making and risk-taking hinge on one’s ability to anticipate and reflect on the
consequences of one’s decision; both are sensitive to frontal lobe disruption (Bechara et al.,
2000), and have been a recent area of interest in cannabis research. Lane et al. (2005) found
that subjects exposed to a high dose of THC (3.6%) demonstrated significantly greater risk-
taking than subjects receiving lower doses of THC. Conversely, similar studies by
Ramaekers et al. (2006) and McDonald et al. (2003) found no significant differences in risk-
taking between groups.
Vadhan et al. (2007) tested chronic, daily cannabis users after administering placebo, light
(1.8%), or heavy (3.9%) THC and found no differences in performance on decision-making
tasks. The researchers did find, however, that both THC groups were significantly slower in
decision-making than the placebo group. On another decision-making task Ramaekers et al.
(2006) found that, compared to the placebo group, subjects receiving THC were
significantly less likely to make correct decisions. Additionally, those in the THC groups
required longer planning times (latency to respond) than the placebo group. It appears then
that the acute effects of cannabis on decision making and risk taking are somewhat
discrepant and may indicate a dissociable difference in functions. Overall, there is evidence
that acute cannabis use has observable deficits in aspects of planning and decision making
particularly with regard to response speed, accuracy and latency.
Inhibition and Impulsivity
Drugs of abuse are often linked to an array of socially unacceptable, poorly controlled, and
maladaptive behaviors, collectively referred to as impulsivity. Few controlled studies have
investigated the effects of acute doses of cannabis on impulsive behavior. In one study of 37
adults with a history of light cannabis use, acute intoxication with a high dose of THC
resulted in significant impairment on a measure of impulsivity (McDonald et al., 2003).
Another study (Ramaekers et al., 2006) found similar impairment on a task of inhibition in
intoxicated, chronic cannabis users. Given this evidence, it appears that acute cannabis use
promotes more impulsive behavior and less inhibition of maladaptive responses.
Working Memory
Another measure of executive function is working memory. For more than 40 years,
researchers have shown that cannabis consumption impairs working memory, or the ability
to hold and manipulate information and remember it following a short delay (Tinklenberg et
al., 1970; Miller et al., 1977; Heishman et al., 1997). This finding has been replicated in
present day research. In a recent study of chronic cannabis users, Hart et al. (2001) found
that acute intoxication resulted in significant impairment in working memory, and those
subjects receiving a higher dose of THC (3.9%) took significantly longer to complete the
task.
Verbal Fluency
Morrison et al. (2009) studied verbal fluency, or the ability to generate letters or words in a
set amount of time, in recreational cannabis users 30 minutes after administering placebo or
moderate (2.5mg) THC. Compared with controls, they found no impairing effects on verbal
fluency abilities.
Summary of Acute Effects of Cannabis on Executive Functions
Research assessing the effects of acutely administered doses of cannabis on executive
functioning has yielded mixed results (see Table 2). Evidence of the impairing effects of
cannabis intoxication on attention and concentration is stronger in less experienced cannabis
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users than those with established drug tolerance; attention and concentration in the latter
group is disrupted more by acute abstinence than acute cannabis administration, probably as
a function of neuroadaptation to chronic, heavy cannabis use. Comparable effects were
observed on tasks involving information processing, a function that is a basic building block
for attention and concentration. Acute cannabis use has generally been found to impair
aspects of planning and decision-making, e.g. in terms of response speed, accuracy and
latency. Some studies also found risk-taking increased with higher doses of cannabis. Acute,
impairing effects of cannabis on tasks assessing inhibition and impulsivity have also been
documented. Verbal fluency appears intact following acute cannabis administration, but
cannabis-related impairments in aspects of working memory are well-established.
RESIDUAL EFFECTS OF CANNABIS ON EXECUTIVE FUNCTIONS (7 hours
to 20 days after last use)
Cannabis use may impact executive functions for several weeks. The literature reviewed for
the residual effects of cannabis use on executive functions covers the period of time from 7
hours to 20 days since last use.
Attention and Concentration
Pope et al. (2001; 2002) tested current, heavy cannabis users, former heavy cannabis users,
and control subjects on days 0, 1, 7 and 28 of abstinence. On all 4 occasions, no significant
differences were found on attentional abilities. This finding was replicated by Jager et al.
(2006). Contrary to those findings, however, Solowij et al. (1995; 2002) assessed long- and
short-term cannabis users who were abstinent for 24 hours and found that their attention was
significantly impaired and they showed longer reaction times to complete the tasks,
compared with controls. Solowij et al. (2002) also reported impaired information processing
abilities in cannabis users compared with controls. Another study (Hermann et al., 2007) of
recreational cannabis users with an unknown duration of abstinence reported poorer
performance on attentional tasks, compared with controls.
Wadsworth et al. (2006) examined attentional capacities in “real world” situations; that is,
right before work and immediately after work, at both the beginning and end of the work
week. They found that, compared with controls, cannabis subjects had significantly impaired
attention both at the beginning of the work week and at the end, which was significantly
correlated with duration of cannabis use. This finding has implications for everyday
activities, suggesting that even with abstinence, some attentional deficits remain.
Decision-Making and Risk-Taking
In the single study assessing this domain, Whitlow et al. (2004) evaluated the performance
of chronic, heavy cannabis users with at least 12 hours of abstinence on a task that simulates
decision-making and risk-taking. Compared with controls, the cannabis users had
significantly impaired decision-making capacities and greater risk-taking tendencies. More
research is needed to augment the finding of residual cannabis effects on decision-making
and risk-taking.
Inhibition and Impulsivity
One of the first groups (Pope et al., 1996) to study inhibition and cognitive flexibility in
cannabis users examined heavy and light users after a minimum of 19 hours of abstinence.
Heavy cannabis users demonstrated significantly more errors of inhibition and perseveration
compared with light users. Solowij et al. (2002) replicated these findings in cannabis users
after at least 12 hours of abstinence. The severity of these deficits was correlated with years
of use. Several other researchers have found a similar pattern of impairment (Aharonovich et
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al., 2008; Cunha et al, 2010). In contrast, a number of researchers found no residual effects
of cannabis use on inhibition or impulsivity (Whitlow et al., 2004; Gruber et al., 2005;
Hermann et al., 2007); however, these studies had small sample sizes (e.g. N=10) and the
length of abstinence was unspecified or was highly variable, ranging from 12 hours to 18
years. Thus, although clear indication exists of impairment after acute cannabis intoxication,
the residual effects appear less consistent. One possible explanation may be the samples
sizes used in these studies lacked statistical power to detect differences. Studies that found
significant differences had much larger sample sizes than those detecting no differences.
Working Memory
Pope et al. (1996) found no differences in working memory abilities between recently
abstinent (19 hours) heavy and light cannabis users compared with control subjects. In
addition, no significant differences were found in working memory abilities of recently
abstinent cannabis users across multiple studies (e.g., Kanayama et al., 2004; Jager et al.,
2006; Solowij et al., 2002; Whitlow et al., 2004; Fisk et al., 2008).
Verbal Fluency
Pope et al. (1996) also studied verbal fluency in cannabis users and, while they did not have
a control group for comparison, they found no differences between heavy users and light
users after a minimum of 19 hours of abstinence. More recently Fisk et al. (2008) replicated
this finding in light users relative to controls. In contrast, McHale and Hunt (2008) analyzed
verbal fluency in regular cannabis users (past 6 months), recent cannabis users (past 7 days),
and controls. Subjects were tested 24 hours after their last use and significant differences in
verbal fluency were found between the cannabis and control groups. It is unclear why these
findings are discrepant; however, one possible explanation is the difference in samples used.
Pope et al. (1996) did not use a control group and Fisk et al. (2008) used very light users,
while McHale and Hunt (2008) used more regular, frequent users.
Summary of the Residual Effects of Cannabis on Executive Functions
Investigations on the residual effects of cannabis on executive functioning show that
recently abstinent cannabis users (7 hours to 20 days) may experience impairment in certain
aspects of executive functioning. Attention, concentration, inhibition and impulsivity may or
may not continue to be impaired during the interval associated with the elimination of THC
and its metabolites from the brain. Decision-making and risk-taking capabilities have not
been thoroughly studied during this period, but a single study by Whitlow et al. (2004)
suggests that these abilities are impaired. In contrast to the acute effects of cannabis in
working memory, deficits as a function of residual cannabis effects have not been found.
Findings for verbal fluency are somewhat mixed, but may be due in part to sample
differences in degree of cannabis exposure. Studies showing the greatest deficits in
executive functioning used subjects who had been smoking heavy amounts of cannabis for
long periods of time. It is likely that residual impairments are linked to the duration and
quantity of cannabis use.
LONG-TERM EFFECTS OF CANNABIS ON EXECUTIVE FUNCTIONS (3
weeks or longer since last use)
The long-term effects of cannabis use have received the greatest research attention in recent
years. Nevertheless, this area of the literature has been fraught with inconsistencies in
findings and is complicated by discrepant definitions of what constitutes “long-term
effects.” For the purpose of this review, long-term effects refers to 21+ days since last using
cannabis, which ensures that both the acute and residual effects of cannabis in the brain have
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been eliminated. Only a handful of researchers have examined these long-term effects of
cannabis use on executive functions, as reviewed below.
Attention and Concentration
In five of seven studies, no attention or concentration impairments were found in subjects
who had remained abstinent from 28 days to one year (Lyons et al., 2004; Pope et al., 2001;
2002; 2003; Verdejo-Garcia et al., 2005). Conversely, of the two remaining studies, Solowij
(1995) examined cannabis users abstinent from 6 weeks to 2 years and found significant
impairment in selective attention and concentration. Likewise, Bolla and colleagues (2002)
found long-term deficits in attention and concentration in a sample of heavy, chronic
cannabis users, abstinent for approximately 28 days. It is possible that these disparate
findings are attributable to impairment in basic information processing skills rather than
higher level attentional abilities. Information processing has not been examined in long-term
cannabis abstinence.
Decision-Making and Risk-Taking
Another cognitive construct recently examined in abstinent cannabis users is decision-
making and risk-taking. One study compared cannabis users, cocaine users, and control
subjects who were abstinent 25 days and found a trend towards significant impairment in
decision-making and risk-taking in the cannabis group compared with non-cannbis using
controls and no differences in performance when compared with the cocaine group
(Verdejo-Garcia et al., 2006).
Inhibition and Impulsivity
The majority of research assessing the long-term effects of cannabis on inhibition and
impulsivity have used two different tests: the Stroop Test or the Wisconsin Card Sort Test
(WCST). Studies using the Stroop test have consistently found no significant differences
between cannabis and control groups (Lyons et al., 2004; Pope et al., 2001; 2002; 2003;
Verdejo-Garcia et al., 2005). In contrast, studies using the WCST have all found significant
differences (Bolla et al., 2002, Pope et al., 2001; 2002; 2003), with the exception of Lyons et
al. (2004). That study examined male monozygotic twins who used varying amounts of
cannabis (>1 time/wk for a minimum of 1 year versus < 5 times in their life time) and found
no differences between the siblings. The Stroop test requires active selection and, as a result,
may require inhibition of some aspects of attention to produce the appropriate response
(Kosmidis et al., 2006) whereas the WCST requires additional functions such as
conceptualizing, developing, and testing hypotheses, as well as inhibition (Huguelet et al.,
2000). Both tests require the ability to perform set shifting and maintenance. It is possible
that the discrepant findings in the cannabis literature may represent intact set shifting and
maintenance but impairment in concept formation, planning and sequencing.
Working Memory
The only known study to analyze the long-term effects of cannabis on working memory is
Vardejo-Garcia and colleagues (2005). This study did not find any significant differences
between abstinent cannabis users and polysubstance abusers. Perhaps studies using a control
group may yield more definitive findings in this area.
Verbal Fluency
Pope et al., (2001; 2002; 2003) examined verbal fluency after 28 days of abstinence.
Performance differences between groups reported in the earlier studies were nonsignificant;
however, the most recent study showed significant differences between groups on verbal
fluency. This later study divided the cannabis groups based on age of onset (early and late)
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and compared their performance with a control group. Early onset cannabis users (who
began smoking before age 17) demonstrated significant impairments in verbal fluency
compared with controls. These findings suggest that age of onset, and possibly years of use,
mediates the impact of long-term effects of cannabis on verbal fluency.
Summary of the Long-Term Effects of Cannabis on Executive Functions
Cannabis appears to continue to exert impairing effects in executive functions even after 3
weeks of abstinence and beyond. While basic attentional and working memory abilities are
largely restored, the most enduring and detectable deficits are seen in decision-making,
concept formation and planning. Verbal fluency impairments are somewhat mixed at this
stage. Similar to the residual effects of cannabis use, those studies with subjects having
chronic, heavy cannabis use show the most enduring deficits.
TREATMENT IMPLICATIONS
Few fully controlled treatment studies for cannabis dependence have been published and
those focus primarily on motivation enhancement therapy (MET), cognitive-behavioral
therapy (CBT), or a combination of the two (Nordstrom and Levin, 2007). High relapse rates
were found, which were comparable to those for alcohol, tobacco, and other drugs of abuse,
but were better than those for a delayed treatment control group (e.g., Stephens et al., 2000).
A review of these studies by Nordstrom and Levin (2007) concluded that psychotherapy has
been shown to reduce cannabis use, but that no form of psychotherapy performs
significantly better than another in terms of reduced use and longer psychotherapy studies do
not provide any added benefit over shorter studies (i.e., 3 months versus up to 15 months).
When a patient presents for treatment with a cannabis use problem, the treatment provider
may wish to consider obtaining a neuropsychological assessment of executive functions, as
deficits may have important implications for treatment outcome. Neuropsychological studies
in adult cannabis users show deficits in multiple areas of executive functioning (e.g.,
attention, decision-making, inhibition). As previously discussed, deficits in executive
functioning may be long lasting in some individuals and may impact everyday functioning.
In addition, it is important to determine the age of onset of cannabis use, as cannabis use
typically begins in adolescence, while the brain is still maturing. A number of studies
examining executive function across adolescence and early adulthood found abilities such as
planning, inhibition, and decision-making continue to develop into early adulthood (Romine
and Reynolds, 2005; Rubia et al., 2006; Eshel et al., 2007). Cannabis use throughout
adolescence and young adulthood may impair achievement of such developmental
milestones in executive functioning such that deficits persist after establishing abstinence.
Behavioral therapies for the treatment of cannabis dependence rely on intact cognitive
functions, yet the implications of cannabis-related cognitive impairments on treatment
outcome have received little attention. On a related note, studies in alcohol-dependent
subjects suggest that executive function impairments have a negative impact on treatment
success (Gottschalk et al., 2001; Bates et al., 2006). Cognitive impairment has also been
generally associated with poorer drug abuse treatment outcomes (Crawford, 1978; O’Leary
et al., 1979; Abbott and Gregson, 1981; see also Aharonovich et al., 2008) and these deficits
have been found to impede acquisition of new coping behaviors (McCrady and Smith,
1986), learning and retention of new material (Alterman and Hall, 1989), and to increase the
likelihood of treatment dropout (Teichner et al., 2002).
The long-term executive functioning deficits associated with cannabis dependence and the
associated risks for poor treatment outcome suggests that cognitively impaired cannabis
users may not respond optimally to standard cognitively oriented treatment, such as CBT
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(Aharonovich et al., 2008). In fact, concern has been expressed that cognitive therapy
approaches may not be effective with patients who have cognitive deficits (Verdejo-Garcia
et al., 2004). A first-line approach may be to expose these patients to cognitive rehabilitative
strategies such as encouraging them to check and double-check their work, to give
themselves ample time to complete a task, to build in delays before responding so they can
weigh the costs and benefits of their actions instead of reflexively responding to situations
and to write things down and use repetition and cues to remember important tasks and
information. More research is needed in this area, both to better understand the complex
effects of executive functioning and treatment outcome and to identify the methods for
optimizing treatment outcome in patients with cannabis-related impairments in executive
function (Blume and Marlatt, 2009).
CONCLUSION
Prevalence rates for cannabis use have increased in recent years (SAMHSA 2007), and as
such, chronic, heavy cannabis use is a growing health concern. Research on the effects of
cannabis on cognition has generally lagged behind studies on the cognitive effects of
alcohol, cocaine, methamphetamine and heroin, and only recently appears to be gaining
momentum. Even less attention has been given to the effects of cannabis on executive
functions. There are some important methodological differences to take into consideration
when interpreting the sometimes disparate results of studies of cannabis effects on executive
functions, such as the recency, amount, duration and age of onset of cannabis use.
The trajectory of effects of cannabis on executive functions follows an interesting pattern of
recovery of some functions and persisting deficits in others (see Table 2). The acute effects
of cannabis use are evident in attentional and information processing abilities with recovery
of these functions likely after a month or more of abstinence. Decision-making and risk-
taking problems aren’t necessarily evident immediately after smoking; however, if cannabis
use is heavy and chronic, impairments may emerge that do not remit with abstinence,
particularly if heavy use was initiated in adolescence such that maturation of executive
functions was not achieved. Acute cannabis use impairs inhibition and promotes impulsivity,
and over a period of abstinence, these deficits are most evident in tasks that require concept
formation, planning and sequencing abilities. Working memory is significantly impaired
following acute exposure to cannabis; however, these deficits resolve with sustained
abstinence. Evidence is less clear in regards to verbal fluency abilities; however, research
suggests that chronic, heavy use may impact verbal fluency abilities even after long-term
abstinence. The long-term effects of cannabis on executive function is most clearly
demonstrated when studies use chronic, heavy cannabis users, as opposed to light,
occasional users. Yet even occasional cannabis use can acutely impair attention,
concentration, decision-making, inhibition, impulsivity and working memory.
An understanding of the effects of cannabis use on executive functions has considerable
practical utility in the clinical setting. The consolidation of findings in this review can
provide clinicians with an overview of the documented effects of cannabis use on executive
functions as they relate to age of onset, duration, quantity and recency of use with
consequent treatment implications. With this information, clinicians can inform their
patients who are regular, heavy, cannabis users of the cognitive liabilities associated with
continued use, and better understand the impairments their cannabis-abusing patients
experience in comprehending, processing, and following-through on important health and
treatment advice relevant to sustaining their recovery.
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Acknowledgments
Supported by the NIH grant P20 DA024194
References
Abbott MW, Gregson RA. Cognitive dysfunction in the prediction of relapse in alcoholics. J Stud
Alcohol 1981;42(3):230–43. [PubMed: 7306259]
Aharonovich E, Brooks AC, Nunes EV, Hasin DS. Cognitive deficits in marijuana users: Effects on
motivational enhancement therapy plus cognitive behavioral therapy treatment outcome. Drug
Alcohol Depend 2008;95(3):279–83. [PubMed: 18329188]
Alterman AI, Hall JG. Effects of social drinking and familial alcoholism risk on cognitive functioning:
null findings. Alcohol Clin Exp Res 1989;13(6):799–803. [PubMed: 2690666]
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4.
Washington DC: American Psychiatric Press; 1994.
Bates ME, Pawlak AP, Tonigan JS, Buckman JF. Cognitive impairment influences drinking outcome
by altering therapeutic mechanisms of change. Psychol Addict Behav 2006;20(3):241–53.
[PubMed: 16938062]
Bechara A, Damasio H, Damasio AR. Emotion, decision making and the orbitofrontal cortex. Cereb
Cortex 2000;10(3):295–307. [PubMed: 10731224]
Blume AW, Marlatt GA. The role of executive cognitive functions in changing substance use: what we
know and what we need to know. Ann Behav Med 2009;37(2):117–25. [PubMed: 19330395]
Bolla KI, Brown K, Eldreth D, Tate K, Cadet JL. Dose-related neurocognitive effects of marijuana
use. Neurology 2002;59(9):1337–43. [PubMed: 12427880]
Bolla KI, Eldreth DA, Matochik JA, Cadet JL. Neural substrates of faulty decision-making in abstinent
marijuana users. Neuroimage 2005;26(2):480–92. [PubMed: 15907305]
Brook JS, Stimmel MA, Zhang C, Brook DW. The association between earlier marijuana use and
subsequent academic achievement and health problems: a longitudinal study. Am J Addict
2008;17(2):155–60. [PubMed: 18393060]
Crawford RJ. Treatment of alcoholism. N Z Med J 1978;88(624):419. [PubMed: 282499]
Cunha PJ, Nicastri S, de Andrade AG, Bolla KI. The frontal assessment battery (FAB) reveals
neurocognitive dysfunction in substance-dependent individuals in distinct executive domains:
Abstract reasoning, motor programming, and cognitive flexibility. Addict Behav 2010;35(10):
875–81. [PubMed: 20584570]
Dosher, B.; Sperling, G. A century of human information processing theory: Vision, attention,
memory. In: Hochberg, J., editor. Handbook of Perception and Cognition, Perception and
Cognition at Century’s End: History, Philosophy, Theory. United Kingdom: Academic Press Inc;
1998. p. 199-252.
Eshel N, Nelson EE, Blair RJ, Pine DS, Ernst M. Neural substrates of choice selection in adults and
adolescents: development of the ventrolateral prefrontal and anterior cingulate cortices.
Neuropsychologia 2007;45(6):1270–9. [PubMed: 17118409]
Fals-Stewart W. Ability to counselors to detect cognitive impairment among substance-abusing
patients: an examination of diagnostic efficiency. Exp Clin Psychopharmacol 1997;5(1):39–50.
[PubMed: 9234038]
Ferraro DP. Acute effects of marijuana on human memory and cognition. NIDA Res Monogr
1980;31:98–119. [PubMed: 6775234]
Fisk JE, Montgomery C. Real-world memory and executive processes in cannabis users and non-users.
Journal of Psychopharmacology 2008;22(7):727–36. [PubMed: 18208908]
Gottschalk C, Beauvais J, Hart R, Kosten T. Cognitive function and cerebral perfusion during cocaine
abstinence. Am J Psychiat 2001;158(4):540–45. [PubMed: 11282686]
Grady, CL. Neuroimaging and activation of the frontal lobes. In: Miller, BL.; Cummings, JL., editors.
The human frontal lobes: function and disorders. New York: Guilford Press; 1999. p. 196-230.
Crean et al. Page 10
J Addict Med. Author manuscript; available in PMC 2012 March 1.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Grant I, Gonzalez R, Carey CL, Natarajan L, Wolfson T. Non-acute (residual) neurocognitive effects
of cannabis use: a meta-analytic study. J Int Neuropsychol Soc 2003;9(5):679–89. [PubMed:
12901774]
Grotenhermen F. Pharmacokinetics and pharmacodynamics of cannabinoids. Clin Pharmacokinet
2003;42(4):327–60. [PubMed: 12648025]
Gruber SA, Yurgelun-Todd DA. Neuroimaging of marijuana smokers during inhibitory processing: a
pilot investigation. Brain Res Cogn Brain Res 2005;23(1):107–18. [PubMed: 15795138]
Haney M, Ward AS, Comer SD, Foltin RW, Fischman MW. Abstinence symptoms following smoked
marijuana in humans. Psychopharmacology (Berl) 1999;141(4):395–404. [PubMed: 10090647]
Hart CL, van Gorp W, Haney M, Foltin RW, Fischman MW. Effects of acute smoked marijuana on
complex cognitive performance. Neuropsychopharmacology 2001;25(5):757–65. [PubMed:
11682259]
Heishman SJ, Arasteh K, Stitzer ML. Comparative effects of alcohol and marijuana on mood,
memory, and performance. Pharmacol Biochem Behav 1997;58(1):93–101. [PubMed: 9264076]
Hermann D, Sartorius A, Welzel H, Walter, et al. Dorsolateral prefrontal cortex N-acetylaspartate/total
creatine (NAA/tCr) loss in male recreational cannabis users. Biol Psychiat 2007;61(11):1281–89.
[PubMed: 17239356]
Huestis MA, Mitchell JM, Cone EJ. Urinary excretion profiles of 11-nor-9-carboxy-delta 9-
tetrahydrocannabinol in humans after single smoked doses of marijuana. J Anal Toxicol
1996;20(6):441–52. [PubMed: 8889681]
Huguelet P, Zanello A, Nicastro R. A study of visual and auditory verbal working memory in
schizophrenic patients compared to healthy subjects. Eur Arch Psychiatry Clin Neurosci
2000;250(2):79–85. [PubMed: 10853923]
Jager G, Kahn RS, Van den Brink W, Van Ree JM, Ramsey NF. Long-term effects of frequent
cannabis use on working memory and attention: an fMRI study. Psychopharmacology
2006;185(3):358–68. [PubMed: 16521034]
Kanayama G, Rogowska J, Pope HG, Gruber SA, Yurgelun-Todd DA. Spatial working memory in
heavy cannabis users: a functional magnetic resonance imaging study. Psychopharmacology
2004;176(3–4):239–47. [PubMed: 15205869]
Kelleher LM, Stough C, Sergejew AA, Rolfe T. The effects of cannabis on information-processing
speed. Addict Behav 2004;29(6):1213–9. [PubMed: 15236825]
Kosmidis MH, Bozikas VP, Zafiri M, Karavatos A. Shared cognitive processes underlying
performance on the Wisconsin Card Sorting Test and the Stroop Test in patients with
schizophrenia: a measurement artifact? Neurosci Lett 2006;409(3):234–8. [PubMed: 17030094]
Lane SD, Cherek DR, Tcheremissine OV, Lieving LM, Pietras CJ. Acute marijuana effects on human
risk taking. Neuropsychopharmacology 2005;30(4):800–9. [PubMed: 15775958]
Luria LW. The future: “Where are you rascally rabbit?.” (Elmer Fudd). Plast Reconstr Surg
2002;110(7):1797–8. [PubMed: 12447069]
Lyons MJ, Bar JL, Panizzon MS, et al. Neuropsychological consequences of regular marijuana use: a
twin study. Psychol Med 2004;34(7):1239–50. [PubMed: 15697050]
McCrady BS, Smith DE. Implications of cognitive impairment for the treatment of alcoholism.
Alcohol Clin Exp Res 1986;10(2):145–9. [PubMed: 3521371]
McDonald J, Schleifer L, Richards JB, de Wit H. Effects of THC on behavioral measures of
impulsivity in humans. Neuropsychopharmacology 2003;28(7):1356–65. [PubMed: 12784123]
McHale S, Hunt N. Executive function deficits in short-term abstinent cannabis users. Hum
Psychopharm Clin 2008;23(5):409–15.
Miller LL, McFarland DJ, Cornett TL, Brightwell DR, Wikler A. Marijuana: effects on free recall and
subjective organization of pictures and words. Psychopharmacology (Berl) 1977;55(3):257–62.
[PubMed: 414287]
Morrison PD, Zois V, McKeown DA, et al. The acute effects of synthetic intravenous Delta9-
tetrahydrocannabinol on psychosis, mood and cognitive functioning. Psychol Med 2009;39(10):
1607–16. [PubMed: 19335936]
Nordstrom BR, Levin FR. Treatment of cannabis use disorders: a review of the literature. Am J Addict
2007;16(5):331–42. [PubMed: 17882603]
Crean et al. Page 11
J Addict Med. Author manuscript; available in PMC 2012 March 1.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
O’Leary MR, Donovan DM, Chaney EF, Walker RD. Cognitive impairment and treatment outcome
with alcoholics: preliminary findings. J Clin Psychiatry 1979;40(9):397–8. [PubMed: 479116]
Pope HG, Gruber AJ, Hudson JI, Cohane G, Huestis MA, Yurgelun-Todd D. Early-onset cannabis use
and cognitive deficits: what is the nature of the association? Drug Alcohol Depen 2003;69(3):303–
10.
Pope HG Jr, Gruber AJ, Hudson JI, Huestis MA, Yurgelun-Todd D. Neuropsychological performance
in long-term cannabis users. Arch Gen Psychiatry 2001;58(10):909–15. [PubMed: 11576028]
Pope HG Jr, Gruber AJ, Hudson JI, Huestis MA, Yurgelun-Todd D. Cognitive measures in long-term
cannabis users. J Clin Pharmacol 2002;42(11 Suppl):41S–47S. [PubMed: 12412835]
Pope HG Jr, Gruber AJ, Yurgelun-Todd D. The residual neuropsychological effects of cannabis: the
current status of research. Drug Alcohol Depend 1995;38(1):25–34. [PubMed: 7648994]
Pope HG Jr, Yurgelun-Todd D. The residual cognitive effects of heavy marijuana use in college
students. JAMA 1996;275(7):521–7. [PubMed: 8606472]
Ramaekers JG, Kauert G, van Ruitenbeek P, Theunissen EL, Schneider E, Moeller MR. High-potency
marijuana impairs executive function and inhibitory motor control. Neuropsychopharmacology
2006;31(10):2296–303. [PubMed: 16572123]
Romine CB, Reynolds CR. A model of the development of frontal lobe functioning: findings from a
meta-analysis. Appl Neuropsychol 2005;12(4):190–201. [PubMed: 16422660]
Rubia K, Smith AB, Woolley J, et al. Progressive increase of frontostriatal brain activation from
childhood to adulthood during event-related tasks of cognitive control. Hum Brain Mapp
2006;27(12):973–93. [PubMed: 16683265]
SAMSHA. Results from the 2006 National Survey on Drug Use and Health: National Findings.
Rockville, MD: Office of Applied studies, DHHS; 2006.
SAMSHA. Results from the 2007 National Survey on Drug Use and Health: National Findings.
Rockville, MD: Office of Applied studies, DHHS; 2007.
Solowij N. Do cognitive impairments recover following cessation of cannabis use? Life Sci
1995;56(23–24):2119–26. [PubMed: 7776840]
Solowij N, Michie PT, Fox AM. Differential impairments of selective attention due to frequency and
duration of cannabis use. Biol Psychiatry 1995;37(10):731–9. [PubMed: 7640328]
Solowij N, Stephens RS, Roffman RA, et al. Cognitive functioning of long-term heavy cannabis users
seeking treatment. JAMA 2002;287(9):1123–31. [PubMed: 11879109]
Stephens RS, Roffman RA, Curtin L. Comparison of extended versus brief treatments for marijuana
use. J Consult Clin Psychol 2000;68(5):898–908. [PubMed: 11068976]
Teichner G, Horner MD, Roitzsch JC, Herron J, Thevos A. Substance abuse treatment outcomes for
cognitively impaired and intact outpatients. Addict Behav 2002;27(5):751–63. [PubMed:
12201382]
Tinklenberg JR, Melges FT, Hollister LE, Gillespie HK. Marijuana and immediate memory. Nature
1970;226(5251):1171–2. [PubMed: 5447045]
Vadhan NP, Hart CL, van Gorp WG, Gunderson EW, Haney M, Foltin RW. Acute effects of smoked
marijuana on decision making, as assessed by a modified gambling task, in experienced marijuana
users. J Clin Exp Neuropsychol 2007;29(4):357–64. [PubMed: 17497559]
Verdejo-Garcia A, Lopez-Torrecillas F, Gimenez CO, Perez-Garcia M. Clinical implications and
methodological challenges in the study of the neuropsychological correlates of cannabis,
stimulant, and opioid abuse. Neuropsychol Rev 2004;14(1):1–41. [PubMed: 15260137]
Verdejo-Garcia A, Rivas-Perez C, Lopez-Torrecillas F, Perez-Garcia M. Differential impact of
severity of drug use on frontal behavioral symptoms. Addict Behav 2006;31(8):1373–82.
[PubMed: 16326022]
Verdejo-Garcia AJ, Lopez-Torrecillas F, Aguilar de Arcos F, Perez-Garcia M. Differential effects of
MDMA, cocaine, and cannabis use severity on distinctive components of the executive functions
in polysubstance users: a multiple regression analysis. Addict Behav 2005;30(1):89–101.
[PubMed: 15561451]
Wadsworth EJK, Moss SC, Simpson SA, Smith AP. Cannabis use, cognitive performance and mood in
a sample of workers. Journal of Psychopharmacology 2006;20(1):14–23. [PubMed: 16204329]
Crean et al. Page 12
J Addict Med. Author manuscript; available in PMC 2012 March 1.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Whitlow CT, Liguori A, Livengood LB, et al. Long-term heavy marijuana users make costly decisions
on a gambling task. Drug Alcohol Depend 2004;76(1):107–11. [PubMed: 15380295]
Crean et al. Page 13
J Addict Med. Author manuscript; available in PMC 2012 March 1.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
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TABLE 1
Definitions of Key Aspects of Executive Functioning
Aspect of Executive
Functioning Definition
Attention Process of selectively attending to one aspect of the environment while ignoring other things, includes divided
and sustained attention to target stimuli
Concentration Intense mental application
Decision Making Process of selecting a course of action among several alternatives
Impulsivity Initiation of behavior without adequate forethought as to the consequences of actions
Inhibition Imposing restraint upon behavior or another mental process; resistance to prepotent responding
Reaction Time Lapse of time between the presentation of a stimulus and a response
Risk Taking Engaging in behaviors that have the potential to be harmful or dangerous
Verbal Fluency Generating multiple, verbal responses associated with a specified conceptual category
Working Memory Ability to hold and manipulate information and remember it following a short delay
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TABLE 2
A Summary of Research Findings on the Effects of Cannabis on Executive Functions
Executive Function Measured Acute Effects Residual Effects Long-Term Effects
Attention/Concentration Impaired (light users)
Normal (heavy users) Mixed findings Largely normal
Decision Making & Risk Taking Mixed findings Impaired Impaired
Inhibition/Impulsivity Impaired Mixed findings Mixed findings
Working Memory Impaired Normal Normal
Verbal Fluency Normal Mixed findings Mixed findings
Note: Acute Effects denotes 0–6 hours after last cannabis use; Residual Effects denotes 7 hours to 20 days after last cannabis use; Long-Term
Effects denotes 3 weeks or longer after last cannabis use.
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