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Article
Improved colour blindness symptoms
associated with recreational psychedelic
use: Results from the Global Drug
Survey 2017
JEC Anthony
1
, A Winstock
2,3
, JA Ferris
4
and DJ Nutt
5
Abstract
It is well documented that psychedelic drugs can have a profound effect on colour perception. After previous research
involving psychedelic drug ingestion, several participants had written to the authors describing how symptoms of their
colour blindness had improved. The Global Drugs Survey runs the world’s largest annual online drug survey. In the
Global Drugs Survey 2017, participants reporting the use of lysergic acid diethylamide or psilocybin in the last 12 months
were asked,
We have received reports from some people with colour-blindness that this improves after they use psychedelics.
If you have experienced such an effect can you please describe it in the box below, say what drug you took and how
long the effect lasted.
We received 47 responses that could be usefully categorised of which 23 described improved colour blindness.
Commonly cited drugs were LSD and psilocybin; however, several other psychedelic compounds were also listed.
Some respondents cited that the changes in colour blindness persisted, from a period of several days to years.
Improved colour blindness may be a result of new photisms experienced in the psychedelic state aligning with pre-
existing concepts of colour to be ascribed a label. Connections between visual and linguistic cortical areas may be
enhanced due to disorder in the brain’s neural connections induced by psychedelics allowing these new photisms and
concepts to become linked. This paper provides preliminary data regarding improved colour blindness accompanying
recreational psychedelic use which may be further investigated in future iterations of the Global Drugs Survey or in a
stand-alone Global Drugs Survey-managed psychedelics survey.
Keywords
colour vision, LSD, psychedelics, psilocybin
Introduction
‘Mescaline raises all colours to a higher power and
makes the percipient aware of innumerable fine
shades of difference, to which, at ordinary times he is
completely blind’ (Huxley, 1954: 14).
I was completely astonished by the beauty of nature.
Our eyes see just a small fraction of the light in the
world. It is a trick to make a coloured [sic] world,
which does not exist outside of human beings. –
Albert Hofmann
These two quotes are a small fraction of the historical
literature describing how psychedelics greatly alter
one’s ordinary perception of colour. Such altered
perception has been previously assessed in a lab con-
trolled setting; finding changes in spectral patterns and
hue discrimination, which also varies between different
psychedelic drugs (Hartman and Hollister, 1963). This
1
University of Cambridge, UK
2
University College London, UK
3
Global Drug Survey, London UK
4
Centre for Health Services Research, The University of Queensland,
Australia
5
Imperial College London, UK
Corresponding author:
DJ Nutt, Imperial College London, London, UK.
Email: d.nutt@imperial.ac.uk
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DOI: 10.1177/2050324520942345
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challenges our current understanding of the role
of photoreceptors in central colour processing.
However, restrictions around research involving these
drugs made further studies into these phenomena more
challenging.
We had received reports from several people who
participated in our research that after taking a psyche-
delic, their previously colour-blind perception of the
world was changed. One participant said,
All my life I suffered from red-dichromacy/
protanopia ...after psilocybin I viewed Monet’s San
Giorgio Maggiore at Dusk, a painting which I had pre-
viously seen as a dull mass of brown and blue. All of
the colours I was previously unable to see were there on
the screen, and the emotion that I felt made me unable
to speak for about half an hour.
Similar comments were made on online forums such
as Reddit, ‘I’m colour blind, and I’m convinced
shrooms [sic] allows me to see all colours vibrantly’
(Anonymous, 2015). These reports suggested that
some individuals were experiencing improvements in
their colour blindness.
Normal colour vision is trichromatic arising from
comparisons between the differential excitement of
three types of colour-sensing cone in response to cer-
tain wavelengths of light. Colour blindness is an inher-
ited X-linked genetic disorder in which sufferers usually
have one less cone type in the retina. This results in a
reduced ability to compute spectral differences between
certain colours depending on the wavelength of light
the lost cone was most sensitive to. Psychedelics will
not alter the inherent colour sensing ability of the opti-
cal machinery in the retina; however, they may affect
central processing of the colour signal from the retina
thus affecting colour blindness.
Previous studies have found that psychedelics can
alter the way depressed patients respond to emotional
faces, particularly fearful ones (Roseman et al., 2018),
and a recent systematic review has highlighted that psy-
chedelic use has been associated with permanent
changes to personality in both the acute and long
term (Bouso et al., 2018). This demonstrates the estab-
lished potential of psychedelics to affect our central
processing of emotion and we were interested as to
whether psychedelics could assert similar effects by
improving colour vision in colour-blind people.
Colour-blind synaesthetes have reported experienc-
ing ‘alien’ photisms in relation to certain numbers
(Ramachandran and Hubbard, 2001) showing that
the brain can alter the colour experience beyond
input from the optic nerve. A recent case study has
reported a patient who has experienced synaesthesia
for over seven years since ingesting 75–150 milligrams
of 2C-B (Yanakieva et al., 2019), indicating that some
psychedelic experiences can produce long lasting
changes in perception. In both cases, the input to the
brain from the sense organs is unchanged; however, it
demonstrates the profound and persistent influence that
central processing can have on the sensory experience.
The Global Drugs Survey (GDS) runs the world’s
largest online drug survey and has been running annu-
ally since 2012. To address whether psychedelics
improved colour blindness in recreational psychedelic
users, a question was added to the Psychedelics section
at the end of GDS2017 asking colour-blind partici-
pants if they had noticed changes in their colour blind-
ness association with their use of psychedelics. The aim
was to gather preliminary data regarding this phenom-
enon with the intention of exploring this further in
future iterations of the GDS, if responses suggested
changes occurred at a significant prevalence.
Methods
Data were compiled from the GDS. GDS has been
running annually since 2012 (naming convention
refers to year the data are released, not the year of
collection) and runs the world’s largest annual online
drug survey. The survey uses an anonymous cross-
sectional design. The GDS2017 ran for seven weeks
between the second week of November and end of
December 2016 involving 119,075 participants after
sample cleaning. Direct participant recruitment
occurred through media partnerships in over 20 coun-
tries including outlets such as Vice, The Guardian and
Zeit-on-Line, with secondary recruitment occurring via
sharing of the content on social media such as
Facebook or discussion forums such as Reddit
(Barratt et al., 2017). Multi-institutional ethics approv-
al was obtained from the Kings College London
Research Ethics Committee 11671/001: Global Drug
Survey, University of Queensland (No. 2017001452)
and The University of New South Wales (HREC
HC17769) Research Ethics Committees.
As part of GDS2017 a series of questions were
included at the end of the Psychedelics section, to
probe the effects of recreational use of psychedelics
on colour blindness. Participants reporting the use of
LSD or psilocybin in the last 12 months were asked,
We have received reports from some people with
colour-blindness that this improves after they use psy-
chedelics. If you have experienced such an effect can
you please describe it in the box below, say what drug
you took and how long the effect lasted.
The information obtained was received in the form of
‘open-ended’ qualitative anecdotes. The survey was
2Drug Science, Policy and Law
translated into 14 main languages including German,
Italian, French, Danish, Portuguese, Spanish,
Hungarian, Flemish and Polish.
Responses were categorised as follows:
1. Colour blind and colour change (EXPERIENCED)
2. Colour blind and no colour change (NOT
EXPERIENCED)
For a response to be marked ‘experienced’, the
respondent had to imply a marked difference in ability
to distinguish between colours; however, this effect
didn’t have to extend beyond the period of intoxica-
tion. Since the question was asked, ‘If you have
experienced such an effect’, implying both colour
blindness and improvement, respondents weren’t
required to positively identify as colour blind. Several
respondents reported experiences of increased colour
intensity; however, these were marked negative as this
did not prove an increased ability to discern between
colours.
An ideal ‘experienced’ response (ID 19670) was,
‘LSD, I’m red/green colour blind and the effect lasted
the following 3 or 4 days’.
An ideal ‘not experienced’ response (ID 13385) was,
‘I have deuteranopia, but unfortunately I didn’t sense
any change in my colour perception on psilocybin.
(I also figured this out using example images for
people with colour blindness)’.
Graphs were constructed using RStudio (RStudio
Team, 2019).
Results
The question received 382 responses from 10 different
countries of which 47 responses could be categorised
with regards to the question. Of the categorised
responses, 23 experienced and 24 didn’t experience
improved colour blindness symptoms (Figure 1).
Despite the low number of categorised responses,
there was a sufficient number of respondents reporting
improved colour blindness to suggest that, in some
people, recreational psychedelic use may improve
colour blindness.
We were interested in whether the specific psyche-
delic drug used would influence the prevalence of
improved colour blindness being experienced. Of the
23 respondents who experienced the effect, 15 indicated
the drug used, with some indicating multiple drugs.
LSD and psilocybin mushrooms were the most com-
monly cited psychedelic drugs (Figure 2). There were
single mentions of novel psychedelic substances used
with which this effect occurred. This included substitut-
ed 2C family drugs such as 25I-NBOMe and 2C-C
and several novel substituted tryptamines such as
5-MeO-DMT and 4-HO-MET. Responses did not indi-
cate that a specific drug induced changes in colour
blindness with a greater frequency than other drugs.
The question also asked about the length of time the
changes in colour blindness lasted for. Of respondents
who experienced changes in their colour blindness,
39% indicated that their changed perception continued
for a period after the drug had worn off ranging from
three days to ‘years’. The time frames given for
Figure 1. Graph showing the number of respondents reporting
about changes to their colour blindness following recreational
psychedelic use. Experienced means respondents reported
improved colour blindness, not experienced means respondents
did not report improved colour blindness.
Figure 2. Graph showing the number of times certain drugs
were cited to improve colour blindness symptoms. The ‘other’
category includes substituted 2C family drugs and novel
substituted tryptamines. Some respondents listed multiple drugs.
LSD: lysergic acid diethylamide.
Anthony et al. 3
persistence of this phenomenon beyond the immediate
effects of the drug were largely non-specific and further
quantification was not possible due to the nature of the
responses given.
Discussion
This study explored the effects of recreational psyche-
delic use on colour blindness through a self-reported
survey question included in GDS2017. There were 382
responses to the question of which 47 could be categor-
ised. Of these, 23/47 reported experiencing improved
colour blindness relating to recreational psychedelic
use, defined as an improved ability to discriminate
between colours. Respondents reported a range of
drugs and time frames associated with improved
colour vision. The number of respondents reporting
improved colour blindness suggests that such improve-
ments do occur in a proportion of recreational users of
psychedelics. Psychedelics may facilitate the experience
of an expanded spectrum of colours. In the excited psy-
chedelic state, new communication between cortical
regions may link new photisms to pre-existing concepts
of colours, thus facilitating a new colour experience
and improving colour blindness. The self-reported
anonymous nature of the GDS made it hard to verify
claims and the 20–30 minutes length of the survey
meant responses to this question, placed at the end,
may have been affected by participant fatigue, thus
reducing their quality and utility. In the future, we
plan to run a more in depth GDS managed psyche-
delics survey to further gather reports regarding this
phenomenon.
Psychedelics do not alter the innate nature of the
visual signal from the retina because the defect is of
genetic origin – the result of fewer ‘colour-sensing’
cones in the retina. The signal sent to the primary
visual cortex from the retina likely remains unchanged
under the influence of psychedelics. Colour signals are
then processed, via the ventral visual pathway, in the
V4 region of the occipital cortex and it is from this
point that psychedelics may affect higher order
processing and ultimately perception of colour.
Psychedelics may result in new colours being experi-
enced, termed ‘alien’ photisms. In the psychedelic
state, increased neural plasticity may aid the formation
of associations between new photisms and pre-existing
concepts of colours that were not previously distin-
guished, thus improving the range of colours experi-
enced and improving colour blindness.
Classical psychedelics, such as LSD and psilocybin,
are 5-HT
2A
receptor agonists (Glennon et al., 1984);
however, each psychedelic drug has its own unique
binding profile, particularly regarding other 5-HT
receptor subtypes (Ray, 2010). These differences may
affect the extent to which different psychedelic drugs
can improve colour blindness; however, the nature of
the responses provided did not allow such analysis.
Despite the variation in binding profiles, most psyche-
delic drugs principally agonise the 5-HT
2A
receptor.
Agonism at this receptor depolarises deep-layer pyra-
midal neurons in the prefrontal cortex (Andrade, 2011)
resulting in disordered signalling and a window
of increased neural plasticity, described by
Carhart-Harris et al. (2014) as the ‘Entropic Brain
Hypothesis’. The period of increased uninhibited corti-
cal signalling induced by modulation of the 5-HT
2A
receptor may enable new neural connections to form.
Psilocybin, a classical psychedelic, has been shown to
increase the formation of homological scaffolds of
brain functional networks under fMRI analysis (Petri
et al., 2014) and such changes in brain chemistry may
persist beyond the immediate pharmacological actions
of the drug (Carhart-Harris and Nutt, 2017). We pro-
pose that the new neural networks may enable new
associations between the perceived and linguistically
known colour of objects, altering the experience of
colour perception.
Under the influence of psychedelic drugs, users may
experience an expanded array of colours, possibly as a
result of enhanced entropy in the V4 cortex leading to
over-exaggerated cross visual field comparisons. This
does not necessarily mean the colours seen of objects
are more representative of their true colour, merely a
wider variety of colours are experienced (Hartman and
Hollister, 1963). Some of the colours experienced in
this state may be entirely new to the user. Colour
blind synaesthetes have reported experiencing ‘alien’
photisms, which are reported to not exist within the
range of their normal perception, in relation to certain
numbers (Ramachandran and Hubbard, 2001), show-
ing the ability of the brain to alter the experience of
colour beyond optic nerve input. Thus, the notion of a
new colour being experienced under the influence of
psychedelic drugs is not unfathomable.
The ‘alien’ colours experienced whilst under the
influence of psychedelic drugs may become ascribed
to objects based upon known linguistic ideas of any
object, for example an apple is red or the sky is blue.
Despite having difficulty distinguishing these colours,
depending on the type of colour blindness, individuals
still have a concept of these colours. Congenitally blind
children have been shown to have a 69–80% agreement
in associations of colours relative to their sighted coun-
terparts. For example, yellow may be conceptualised as
a‘happy, nice, shiny colour’. It was shown that these
concepts of colour were purely language based and
relied on being taught their associations (Anthony,
1996). Alien colours experienced in the psychedelic
state may align with the colour-blind user’s conceptual
4Drug Science, Policy and Law
understanding of a colour they are not normally able to
observe. This may be ascribed to certain objects leading
to lexically driven changes in the perception of specific
objects in line with their colour. Such changes would be
unlikely to occur universally or consistently due to dif-
ferent colour associations between individuals coupled
to different sets and settings.
Synaesthesia may be traditionally be thought of as
‘seeing sound’ or mixing of traditional special senses;
however, there are a plethora of other inducer-
concurrent associations (Luke and Terhune, 2013).
There are a variety of explanations for the phenome-
non of synaesthesia including increased neural connec-
tivity in the psychedelic state (Petri et al., 2014)
or cortical disinhibition and hyperexcitability
(Yanakieva et al., 2019). It is feasible that increased
connection between regions of the cortex responsible
for higher colour perception, V4, to concepts of
colour in language centres may occur in the psychedelic
state through ‘noisy’ disordered signalling. New con-
nections between these aforementioned areas of associ-
ation cortex complement Whorfian ideas of colour
discrimination which may affect an individual’s percep-
tions of coloured objects, consequently leading to
the improvement of colour discrimination in the
colour blind.
There is a growing body of evidence to suggest sero-
tonergic hallucinogens can affect recognition of facial
expressions (Rocha et al., 2019). LSD has been shown
to reduce recognition of sad or fearful faces alongside
enhancing emotional empathy (Dolder et al., 2016). In
a different study, the day after a 25-milligram psilocy-
bin treatment, enhanced amygdala responses to emo-
tional faces, particularly fearful ones, were found,
suggesting alterations in the manner in which depressed
patients respond to emotional stimuli (Roseman et al.,
2018). The brain contains concepts of emotions and if
the response to emotional stimuli and their associations
in the brain can be altered it is plausible that our asso-
ciations of colours and thus their perception can be
changed too, particularly because the raw visual signals
entering the brain in the cases of recognising facial
expression and processing colour are constant.
Long term changes in colour blindness, lasting
beyond psychedelic experience, were reported by 39%
of respondents. This would suggest that such effects are
likely to be common in a larger proportion of the
colour-blind population. However, the number of
colour-blind respondents not experiencing this was
likely underreported due to the positive nature of the
question and thus this high proportion is likely an
artefact of the wording. A possible reason for the per-
sistence of changes in colour vision could be the extra-
pharmacological effects of psychedelics such as set and
setting, which likely vary between respondents,
producing lasting changes in neural networks
(Carhart-Harris and Nutt, 2017). Dosage may also
account for this as levels of 5-HT
2A
receptor occupancy
have been shown to correlate with the intensity of
effects experienced (Madsen et al., 2019) which may
complement the extra-pharmacological effects.
However, the design of the GDS study makes it diffi-
cult to control for these factors. There are recorded
instances of psychedelic-induced visual perceptual
changes persisting. Hallucinogen persisting perception
disorder is estimated to have an occurrence of 1/50,000
in regular users of psychedelic drugs (Halpern et al.,
2016) and some case studies have reported symptoms
lasting for months or years (Martinotti et al., 2018).
Recently, a case of acquired synaesthesia was reported
in a 29-year-old male following the use of 2C-B
which had persisted for over seven years (Yanakieva
et al., 2019).
This study found that a proportion of colour-blind
participants reported improved colour blindness fol-
lowing the recreational use of psychedelics, defined as
an improved ability to discern between colours. There
are several limitations to the study. The data consisted
of self-reported anecdotes of variable quality, some of
which proved hard to interpret, thus making accurate
quantification and standardised interpretation difficult.
The reports were self-validated both as to the nature of
the colour blindness and whether this phenomenon was
experienced. Colour blindness is not a unimodal disor-
der and different forms of colour blindness may have
been affected differently. We were unable to obtain this
level of detail with the responses given. The question
was asked in a ‘special section’ at the end of GDS2017
which itself takes 20–30 minutes to complete and
number of usable responses was small, 47/382. Some
responses didn’t relate to the question or were too dif-
ficult to decipher, which may reflect participant fatigue.
Language barriers were unlikely to play a role due to
the wide variety of language translations available.
In future iterations of the GDS, we plan to revisit
this exploratory study and more clearly identify the
nature of pre-existing colour vision deficit and more
specifically assess changes in visual perception, the
drug taken and better quantification of the persistence
of the effects. Rather than a free-text response, partic-
ipants could provide answers in a multiple-choice
format with the question deconstructed into discrete
parts. Due to the length of the standard GDS, a
GDS managed stand-alone psychedelics survey may
be more suitable to minimise participant fatigue. This
would enable a variety of phenomena regarding recre-
ational use of psychedelics to be evaluated, not just
colour perception, such as visual acuity which was
mentioned by several respondents.
Anthony et al. 5
Acknowledgments
The authors would like to thank the participants of the
GDS2017 for giving their time to complete the survey and
making this study possible. They are grateful to Sophia West
for her help in translating the responses into English.
Declaration of conflicting interests
The author(s) declared the following potential conflicts of
interest with respect to the research, authorship, and/or pub-
lication of this article: A Winstock is the owner and founder
of Global Drug Survey (GDS). Global Drug Survey Ltd is an
independent self-funded organisation.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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