Improved colour blindness symptoms associated with recreational psychedelic use: Results from the Global Drug Survey 2017

The study analysed responses to an item embedded in the Psychedelics section of the Global Drug Survey (GDS) 2017, an annual anonymous cross-sectional online survey. GDS2017 ran for seven weeks from mid-November to the end of December 2016 and, after cleaning, included 119,075 participants overall. Recruitment was via media partners across more than 20 countries and secondary sharing on social media and forums. Multi-institutional ethics approval was obtained from institutional committees at King’s College London, the University of Queensland and the University of New South Wales. Participants who reported use of LSD or psilocybin in the prior 12 months were presented with a free-text item asking whether they had experienced an improvement in colour blindness after taking psychedelics, to say which drug they took and to report how long the effect lasted. The question was translated into 14 languages. Responses were later categorised into two groups: 1) colour blind and colour change (labelled EXPERIENCED) and 2) colour blind and no colour change (labelled NOT EXPERIENCED). For a response to count as 'experienced', it had to indicate a marked improvement in the ability to distinguish colours; reports of merely increased colour intensity without improved discrimination were classified as not experienced. The authors noted that because the question phrased ‘‘If you have experienced such an effect’’ respondents were not required explicitly to self-identify as colour blind, and that many replies were free-text narratives of variable clarity. Graphing and basic summary analyses were performed using RStudio. No specialised psychophysical testing, clinical verification of colour vision deficits, or detailed dose-response data were collected within this item.

The free-text item elicited 382 responses from participants across 10 countries, of which 47 responses could be categorised against the defined criteria. Among those 47, 23 respondents (49%) reported an improved ability to discriminate colours following psychedelic use, while 24 respondents (51%) did not report such an improvement. The small number of usable responses limited quantitative inference, but the authors considered the number reporting improvement sufficient to indicate the phenomenon occurs in at least some recreational users. Fifteen of the 23 respondents who reported improvement specified the drug or drugs involved; LSD and psilocybin mushrooms were the most commonly cited. Single mentions included several novel or substituted psychedelics such as 25I-NBOMe, 2C-C, 5-MeO-DMT and 4-HO-MET. The responses did not provide evidence that any specific psychedelic produced the effect more frequently than others. Regarding duration, 39% of those reporting improved colour vision indicated the change persisted beyond the acute intoxication period, with reported persistence ranging from about three days to 'years'. The authors emphasise that these time estimates were non-specific and could not be precisely quantified from the free-text replies.

Anthony and colleagues interpret the self-reported data as preliminary evidence that a subset of people experience an improvement in colour discrimination associated with recreational psychedelic use. They suggest that such changes are plausibly mediated by alterations in central visual processing rather than changes at the retinal level, because congenital colour blindness typically reflects a loss or alteration of cone photoreceptors in the retina. The authors propose a model in which psychedelics induce increased neural plasticity and disordered cortical signalling—linked to agonism at the 5-HT2A receptor and described in the literature as increased cortical entropy—allowing new ‘‘photisms’’ (novel colour experiences) to become associated with pre-existing linguistic concepts of colour. The paper links this account to related phenomena such as drug-induced synaesthesia and long-lasting perceptual changes previously reported after psychedelic use. The authors note parallels with evidence that psychedelics can alter emotional face processing and personality, arguing that if associations for emotion can be reorganised, so too might associations for colour. They caution that reporting bias likely affected their estimates: the question invited positive reports, and responses were self-validated anecdotes without clinical verification of the type or severity of colour blindness. Other limitations highlighted include the small number of usable responses (47/382), potential respondent fatigue because the question was placed near the end of a 20–30 minute survey, variable quality and interpretability of free-text answers, and lack of dose, set-and-setting, or standardised timing information. For future research the authors propose a more focused GDS-managed psychedelics survey or a revised questionnaire embedded in GDS that uses structured multiple-choice items to capture pre-existing colour vision deficits, the specific drug and dose, objective measures of colour discrimination and clearer quantification of persistence. They also note that rare but persistent perceptual disorders, such as hallucinogen persisting perception disorder, have been reported in the literature and that some individual case reports describe long-lasting acquired synaesthesia following psychedelic ingestion. Overall, the authors present this work as an exploratory, hypothesis-generating step pointing to an effect that merits more rigorous follow-up rather than as definitive evidence of long-term restoration of normal trichromatic vision.