Analysis of 3,364 Global Drug Survey 2020 respondents who self-treated with LSD (n=1,996) or psilocybin mushrooms (n=1,368) found broadly favourable self-reported changes across 17 wellbeing and symptom items—largest effects on insight and mood—although 22.5% reported negative effects. Higher intensity, prior advice-seeking, use of psilocybin and treating PTSD predicted better averaged outcomes, while younger age, high intensity and LSD use predicted more negative effects, suggesting potential benefit but a higher adverse-event frequency than in clinical settings and informing safer community practice and clinical research.
Background
Growing numbers of people are using psychedelics for personal psychotherapy outside clinical settings, but research on such use is scarce.
Aims
This study investigated the patterns of use, self-reported outcomes and outcome predictors of psychedelic ‘self-treatment’ of mental health conditions or specific worries/concerns in life.
Methods
We use data from the Global Drug Survey 2020, a large online survey on drug use collected between November 2019 and February 2020. In all, 3364 respondents reported their self-treatment experiences with lysergic acid diethylamide ( N = 1996) or psilocybin mushrooms ( N = 1368). The primary outcome of interest was the 17-item self-treatment outcome scale, items reflecting aspects of well-being, psychiatric symptoms, social-emotional skills, and health behaviours.
Results
Positive changes were observed across all 17 outcome items, with the strongest benefits on items related to insight and mood. Negative effects were reported by 22.5% of respondents. High intensity of psychedelic experience, seeking advice before treatment, treating with psilocybin mushrooms and treating post-traumatic stress disorder were associated with higher scores on the self-treatment outcome scale after averaging values across all 17 items. Younger age, high intensity of experience and treating with LSD were associated with increased number of negative outcomes.
Conclusions
This study brings important insights into self-treatment practices with psychedelics in a large international sample. Outcomes were generally favourable, but negative effects appeared more frequent than in clinical settings. Our findings can help inform safe practices of psychedelic use in the community, and inspire clinical research. Future research can be improved with utilisation of prospective designs and additional predictive variables.
Papers cited by this study that are also in Blossom
Aday, J. S., Davis, A. K., Mitzkovitz, C. M. et al. · ACS Pharmacology and Translational Science (2021)
Aday, J. S., Heifets, B. D., Pratscher, S. D. et al. · Psychopharmacology (2021)
Agin-Liebes, G. I., Lancelotta, R., Uthaug, M. V. et al. · ACS Pharmacology and Translational Science (2021)
Andersen, K. A. A., Carhart-Harris, R. L., Nutt, D. J. et al. · Acta Psychiatrica Scandinavica (2020)
Psychedelics such as LSD and psilocybin have a long history of use for healing, and recent decades have seen a resurgence of clinical research and rising public interest in their therapeutic potential. Kopra and colleagues note that much contemporary use nevertheless occurs outside formal clinical settings — in informal, underground, retreat or community contexts — and that outcomes observed in tightly controlled clinical trials may not generalise to these naturalistic self-administered practices. The authors also highlight that users' mindset and environment ('set and setting') and the presence or absence of interpersonal support are central determinants of psychedelic experiences and their risks and benefits. This study uses data from the Global Drug Survey (GDS) 2020 to examine patterns and outcomes of self-treatment with LSD or psilocybin-containing mushrooms. The investigation aims to describe how people self-treat (including dose-intensity proxies and whether advice was sought), to report self-rated positive and negative outcomes across multiple domains, and to identify predictors of those outcomes with respect to demographics, treatment patterns and the condition or problem treated. The analysis focuses specifically on respondents who indicated either LSD or psilocybin mushrooms as the substance they found most useful for self-treatment within the past year.
Data come from the Global Drug Survey 2020, an annual, anonymous, encrypted online survey open to people aged 16 or older and available in 16 languages; data were collected between 7 November 2019 and 5 February 2020. Multi‑institutional ethical approvals were obtained and participants could skip questions. Access to the relevant GDS sections (demographics and psychedelics) was gained under a data sharing agreement. As a non-probability self-selected sample, the GDS is not representative of the general population but captures a large number of people who use substances in varied contexts. Respondents who reported self-treating a diagnosed condition or a specific worry with psychedelics in the past 12 months were directed to an optional section. From those who had used several substances, participants were asked to select the single substance they had found most useful; this study was restricted to respondents who chose either LSD or psilocybin mushrooms. Participants selected the main condition they were trying to treat from a list (originally 19 categories, reduced to 13 for analysis due to small counts), reported the number of self-treatment occasions in the past year, rated the intensity of the psychedelic experience on a five-level item (from ‘intense psychedelic experience’ to ‘no experience or effects’), and indicated whether they had sought advice beforehand and the source(s) of that advice. Outcomes were measured with two investigator-constructed scales. The primary scale comprised 17 self-treatment outcome items covering well-being, psychiatric symptoms, social–emotional skills and health behaviours; each item was rated on a seven-point scale from −3 (strong negative consequences) to +3 (strongly positive consequences), with N/A available. Internal consistency for the 17 items was high (Cronbach's α = 0.91), but the authors acknowledge the scale was not psychometrically validated beyond that. The second instrument was a 10-item negative outcome checklist; respondents who reported any negative effects rated each item as none, mild, moderate or severe. Because the negative items were ordinal and to create a single summary measure, each negative item was dichotomised (none = 0; any severity = 1) and summed to yield a count variable from 0 to 10. Statistical analyses included descriptive statistics for demographics, patterns of self‑treatment and item-level outcomes, plus multivariable models to examine predictors. The mean score across non-missing items on the 17-item scale was used as the dependent variable in an ordinary least squares regression; predictors were age (continuous), gender (Male/Female/Other), substance used (LSD/psilocybin mushrooms), seeking advice (Yes/No), intensity of experience (5 categories) and condition treated (13 categories). Duration outcomes (originally 12 response categories) were collapsed into three groups (up to 7 days; 1–4 weeks; 1 month or more) and analysed with ordinal regression, with multinomial logistic regression used when proportional‑odds assumptions were violated. The count of negative outcomes was modelled using negative binomial regression to allow for overdispersion. Analyses used complete‑case approaches rather than imputation and applied a Bonferroni-style correction for multiple tests (adjusted significance threshold p = 0.002 based on 21 predictive factors). Sensitivity analyses restricted some models to respondents with fewer than five missing or N/A responses on the outcome items.
From 113,284 respondents to GDS 2020, 10,268 people (13.8%) reported self-treating a psychiatric condition or specific worry with psychedelics in the past year. Of those reporting substances used for self-treatment, 1996 respondents indicated LSD and 1368 indicated psilocybin mushrooms as the single substance they found most useful, yielding an analysis sample of N = 3364. The sample was young (mean age 25.4, SD 8.5), predominantly male (N = 2422; 72.0%) and majority white (N = 2679; 80.3%); 56.5% (N = 1899) reported a lifetime diagnosis of one or more mental health conditions. Descriptive tables and figures in the paper (not reproduced here) show patterns of treatment and item-level responses. On the 17-item outcome scale (range −3 to +3), the mean across items and respondents was 1.42, indicating mild-to-moderate self-reported improvements overall. Half the sample (N = 1573; 50.0%) rated +2 or +3 on at least nine of the items, and 94.6% had a +2 or +3 on at least one item. The highest-scoring items were insight-related and mood: 'changes in my understanding of why I feel the way I do', 'changes in mood or reduced depression', and 'changes in my understanding of my condition or how I relate to it'. Among those reporting strong positive effects on at least one item (N = 2975), most noticed effects within 24 hours (64.3%; N = 1890) and for the majority effects lasted at least four weeks (52.7%; N = 1497); 17.6% (N = 499) reported durations longer than six months. Negative outcomes were reported by 705 respondents, representing 22.5% of the 3136 participants who answered the question about any negative consequences. Among those reporting negatives, the median number of negative outcomes was 5.0 (IQR 3.0–7.0). The most commonly endorsed negative items were 'mental confusion, memory problems, or racing thoughts' and 'feeling disconnected from the world around you'. Onset of negative effects was most commonly within 24 hours (59.7%; N = 410), although 20.1% (N = 138) reported noticing at least one negative outcome more than a week later. Duration of most negative effects was 7 days or less for 54.6% (N = 370) but one month or more for 27.0% (N = 183). A minority sought emergency medical treatment: 28 respondents (4.2% of those reporting negative effects, 0.9% of the total sample) sought emergency care (25 once, 3 more than once). Multivariable analyses showed the OLS model predicting mean 17‑item outcome score was statistically significant but explained little variance (R2 = 0.06; F[21,3004] = 9.36; p < 0.001). After adjustment, self-treatment with LSD was associated with lower mean outcome scores compared with psilocybin mushrooms; having sought advice beforehand was associated with higher outcome scores. Intensity of experience had a strong omnibus effect: higher intensity (the reference being 'high intensity') was associated with higher outcome scores, and 'no experience or effects at all' was associated with the lowest scores. Condition treated also had an omnibus effect; notably, treating PTSD was associated with higher outcome scores compared to treating depression. Age and gender were not associated with the mean outcome score. Sensitivity analysis limited to respondents with fewer missing outcome responses produced comparable results. For duration outcomes, proportional-odds assumptions were violated in some models and multinomial logistic regression was used. The only consistent predictor reported for duration of negative outcomes was age: older age was associated with shorter duration of negative effects. Other predictors (gender, substance, seeking advice, intensity, and condition treated) were not associated with duration of negative outcomes in adjusted models. The authors also report that higher intensity of experience related to both greater positive outcomes and a greater number of negative outcomes, and that younger age, high intensity, and treating with LSD were associated with increased number of negative outcomes in some analyses.
Kopra and colleagues interpret the findings as showing that, in this large international self-selected sample, self-treatment with LSD or psilocybin mushrooms was generally associated with self-reported improvements across a broad range of wellbeing and symptom-related items, with effect timelines resembling those observed in clinical trials. Insight and mood-related outcomes were rated most highly, aligning with prior reports that psychedelic-facilitated personal insight and emotional breakthrough are commonly reported therapeutic processes that can contribute to sustained wellbeing. The authors emphasise that negative outcomes were not uncommon: 22.5% of respondents reported at least one adverse consequence, most commonly transient cognitive or emotional disturbances, and for a minority these persisted beyond four weeks. They note that persisting perceptual changes were reported by 8.5% of respondents but were seldom rated as severe. The study team contrast these rates with findings from contemporary clinical trials, where persisting severe adverse effects have been rare, and suggest that the lack of professional interpersonal support in self-treatment contexts may elevate some risks. Several predictors of outcomes are highlighted. Intensity of the psychedelic experience was among the strongest predictors of positive outcomes and of longer-lasting effects, which mirrors evidence from clinical dosing studies; however, higher intensity was also associated with more negative outcomes. Seeking advice prior to self-treatment was associated with better outcomes and a trend to fewer negatives, with respondents mainly drawing on informal sources (websites, forums, friends) rather than clinicians. Psilocybin mushrooms were associated with slightly better overall outcome scores and fewer negative outcomes than LSD, though the effect size was small. Treating PTSD was associated with higher outcome scores relative to depression, but the authors caution that differences between conditions may reflect baseline severity, comorbidity and sample-size limitations. Younger age was linked to a higher number and longer duration of negative outcomes, which the authors suggest could reflect riskier patterns of use among younger people. The authors acknowledge important limitations: the self‑selected, predominantly young, white and male sample; retrospective self-report with potential recall and expectancy biases; the non-randomised observational design and the instruction to report on the substance each respondent deemed most useful (which can bias comparisons between substances and intensities); lack of validated symptom measures and no baseline morbidity data; modest variance explained by models and the absence of several potentially important predictors (interpersonal support, expectations, personality, exact dose, substance purity and concomitant substance use). Finally, they note that their 17-item scale, while internally consistent, was not psychometrically validated. In conclusion, the study authors propose that these findings can inform harm-reduction efforts and guide future experimental research, while recommending prospective designs and inclusion of additional predictor variables to better understand benefits and risks of self-administered psychedelic use outside clinical settings.
Sample selection. As respondents were asked to report on their self-treatment experiences based on the substance they had found most useful (in case they had self-treated with several substances), this investigation was restricted to those respondents indicating either LSD or psilocybin mushrooms as the substance found most useful. These substances were judged suitable to be analysed together in the same investigation due to current evidence of their similar subjective effects and pharmacological and therapeutic mechanisms of action, similar psychedelic therapy models applied in research, and preliminary evidence of comparable therapeutic outcomes. 17-Item self-treatment outcome scale. Mean scores of the 17 outcome items for each participant were calculated by averaging all values with non-missing data (maximum of 17), with possible values ranging from -3 (strongly negative) to +3 (strongly positive outcomes). N/A responses were coded as missing values and therefore also excluded from the calculations. Cronbach's alpha for the 17 items was excellent, α = 0.91. 10-Item negative outcome scale. Negative outcomes were rated on an ordinal scale, and therefore could not be treated as continuous data. While an ordinal regression model could be applied for predicting responses to a single ordinally rated dependent variable, it is not possible to create any summary statistic of a multiple-item scale which would retain the ordinal nature of the data. Therefore, to create a regression model predicting overall prevalence of negative outcomes across all items, the items were first transformed into binary variables, indicating No/Yes presence of any severity of a negative outcome. In essence, 'None' responses were recoded as '0' (No), and 'mild', 'moderate' and 'severe' as '1' (Yes). Zeros were also coded for all items of those respondents who had earlier indicated not experiencing any negative outcomes, and who therefore were not presented with the 10-item list. Sum scores were then calculated for each respondent, creating a variable reflecting the total number of (mild-tosevere) negative outcomes with a minimum of 0 and maximum of 10. Those with no response to the question on whether negative outcomes were experienced, were excluded from these analyses. In turn, all cases indicating presence of negative outcomes were included in the analyses, regardless of any missing values on subsequent individual outcome items.
This present study investigated patterns and outcomes of psychedelic self-treatment using data from a large international survey of 3364 people reporting on their self-treatment experiences with LSD or psilocybin mushrooms. The most commonly such treated conditions were depression and anxiety, accounting for 60% of the sample. Reported outcomes were generally positive, average outcome scores reflecting mild-to-moderate improvements across items, which lasted beyond 3 weeks for the majority of respondents. 22.5% of participants reported experiencing some negative consequences from their experience but these were rarely severe or long lasting. A number of significant outcome predictors were identified, namely intensity of psychedelic experience, substance used, seeking advice beforehand, condition treated and age. The time scales for reported improvements closely mirror those seen in clinical trials. The top-rated positive outcome items were 'Changes in understanding of why I feel the way I do' and 'Changes in my understanding of my condition and how I relate to it'. Increased insights into oneself and one's condition are one of the most commonly reported psychedelic-induced therapeutic processes and outcomes described both by participants in clinical trials and users in the community. Increased insight obtained during or immediately after a psychedelic experience has been found to be associated with longer-term increases in well-being, mediating the relationship between acute emotional breakthrough and subsequent well-being. Although only a proportion of patients undergoing psychedelic Duration of positive outcomes was asked from those respondents only with a score of +2 or +3 on at least one self-treatment outcome item (N = 2975). Duration of negative outcomes was asked from those respondents only who indicated experiencing any negative outcomes (N = 705). therapy achieve full remission from their psychiatric symptoms, it has been suggested that increased psychological insight obtained from the treatment can improve the ability to manage one's condition and respond to subsequent stressors more adaptively, contributing to sustained outcomes and supporting longterm mental health. Overall, respondents in our survey reported improvements across a wide range of outcomes, with all item averages above zero indicating a positive change. The findings are consistent with previous literature highlighting psychedelics' potential to induce holistic and transdiagnostic therapeutic effects. Reported negative outcomes were mostly related to emotional states as well as some cognitive functions and appeared largely similar to those observed from recreational use. Lasting problems or distortions in perception were reported by 268 respondents corresponding to 8.5% of all self-treaters; however, only 11.6% of those regarded them as severe. These results largely reflect previous research showing such phenomena are not uncommon, but are rarely cited as disabling or severely distressing and therefore rarely meet the criteria for hallucinogen persisting perception disorder (HPPD) recognised in. Such experiences may represent an enduring effect of psychedelics on visual processing, or may represent an increased awareness of the normal breadth of visual experience. Experienced negative effects were usually short lasting, but for a quarter of those reporting negative outcomes, these lasted for over 4 weeks. Based on available evidence, the risks of persisting negative effects appear lower in clinical settings. A review of psychedelic trials conducted at Johns Hopkins, including a total of 250 individuals (both healthy and clinical populations) treated in more than 380 psychedelic sessions up until 2016, found only three participants had reported transient negative psychological effects, all of which eventually resolved. The first treatment-related serious adverse effects were observed only recently in two clinical trials, which reported suicidality, self-harm and psychiatric symptoms in 2-5% of patients receiving an active dose of psilocybin or LSD. No cases of HPPD, sustained psychosis, or sustained cognitive impairment have been reported in modern clinical research. Several cases of re-emergence of traumatic memories during or shortly after treatment have been observed, but in most studies, any resulting distress was reported as resolved during subsequent integration or counselling sessions. In self-treatment contexts, a lack of professional interpersonal support may increase the risk of longer-term difficulties from similar experiences. Of note, we highlight that recording individual subacute adverse effects in psychedelic clinical trials may sometimes be considered inadequate, as assessment of longer-term outcomes is generally focussed on mean changes in symptom scale ratings, and may further be affected by experimenter biases and social desirability bias. Information obtained from our survey was also limited, as durations of outcomes were not rated individually for each item, and the provided list of outcomes was non-exhaustive and lacked an option for an open-ended answer. Despite the relatively low prevalence of severe or persisting adverse effects observed in response to psychedelics, there is an ethical duty for increased research on the predictors, nature, and management of these both in and outside clinical settings, with increasing numbers of people likely to undergo psychedelic experiences. A large majority of respondents had sought advice or information before using psychedelics for self-treatment. Similarly to previous research on psychedelic use, most had obtained advice from online sources, friends or family, while advice from a therapist or doctor was very rarely reported. Having sought advice predicted higher outcome scores and showed a trend towards longer duration of positive outcomes and lower number of negative outcomes. Although these results together indicate informal sources of advice are seemingly useful in most cases, reliance on these also suggests limited availability of reliable and evidence-based harm reduction resources from authorities. Education of therapists and other health and social care workers, alongside efforts to reduce stigma associated with psychedelics and other drugs, could be particularly important to help ensure provision of personal support for people using psychedelics, the importance of which we highlighted previously. The highest intensity of experience was associated with higher outcome scores compared to other intensity levels. This was also related to longer-lasting positive outcomes, with coefficients at each level indicating a linear relationship between intensity and duration. Most modern psychedelic trials use moderate-high doses, aimed to induce 'peak' or 'mystical-type' experiences and/or emotional breakthrough, that have been found to predict symptomatic improvement. Superior efficacy of high doses was also supported by a recent systematic review that identified higher intensity of experience as the main predictor of favourable outcomes from psychedelic treatments; and by a large multicentre trial on psilocybin for depression where a high 25-mg dose demonstrated better outcomes compared to a low-moderate 10-mg dose. However, the highest intensity of experience was also related to more negative outcomes in our study, consistent with previous research showing increasing dosages correlate both with increasing positive and negative acute and sub-acute effects. In both the present study and previous clinical trials, favourable outcomes have also been observed with moderate doses or less intense experiences, which may provide a suitable alternative for those not willing or safely able to experience the full effects of high-dose psychedelics or where extended clinical supervision is not available. In two clinical trials on psilocybin-assisted therapy for depression, an initial moderate dose was administered first to familiarise participants with the drug effects before a high-dose session a few weeks afterwards. These studies reported larger treatment effects to trials using a single high dose, but more research would be needed to confirm the comparative efficacy and importantly, comparative safety and cost-effectiveness of different dosing regimens. Treating with psilocybin mushrooms was associated with higher outcome scores compared to LSD, although with a very small effect. Psilocybin mushrooms were also associated with fewer negative outcomes, reflecting previous findings on recreational use. Modern clinical trials on psychedelics have primarily been conducted with psilocybin in contrast to pre-prohibition era trials mostly using LSD; this change was presumably driven by the lower level of stigma associated with psilocybin and its lower duration of action, but now seems to be supported by preliminary evidence of the drugs' comparative safety profile. Evidence regarding potential differences in therapeutic efficacy remains, however, inconclusive. In a previous survey study by, psychedelic users rated LSD's therapeutic potential and perceived benefits on well-being and physical/mental health marginally higher than psilocybin's. Two recent systematic reviews on outcome predictors of psychedelic treatments found no effect of the specific psychedelic used; although these analyses were highly limited due to small number of studies especially with LSD, as well as high heterogeneity between sample characteristics and methodologies. The first modern experimental study directly comparing the subjective effects of LSD and psilocybin in healthy individuals, adapting a placebo-controlled cross-over design, likewise found largely comparable effects between the substances apart from the longer duration of LSD. Regardless, the presence of more subtle (yet clinically relevant) differences in the experience not captured by the administered measures cannot be ruled out, and may even be expected given for instance the dopaminergic action observed with LSD but not with other classical psychedelics (which, of note, could also account for the higher frequency of adverse effects observed from LSD;. In the present survey, individuals who had self-treated with both LSD and psilocybin mushrooms showed an equal split regarding which drug they indicated preferring more. It is plausible that some specific properties of each substance suit people differently -and higher variability between outcomes related to each substance could be observed within individual subjects, and/or between specific outcomes, than between group averages of total outcomes. An investigation is currently underway comparing intensity and occurrence of specific positive and negative self-treatment outcomes between LSD, psilocybin mushrooms and MDMA, using GDS2020 data. Psychedelics have demonstrated transdiagnostic potential since early research, and our study likewise observed favourable treatment outcomes across various indications treated. These included previously little investigated conditions such as PTSD, bipolar disorder, eating disorders and psychosis; as well as various problems or worries not representing a diagnostic entity in themselves. Respondents treating PTSD demonstrated highest outcome scores on the 17-item scale, with significantly higher scores to the reference category of depression. The potential of classical psychedelics for the treatment of PTSD has been the topic of several recent review articlesand our results bring further validation for the first clinical trials on psilocybin-assisted therapy for PTSD currently underway (NCT05243329, NCT05312151, NCT05554094). However, we highlight that the apparent superiority of outcomes in PTSD in our study could be at least partially attributed to the wide range of comorbidity and impairment associated with this condition, allowing more substantial improvement on a higher number of outcome items. Besides the unmeasured variability in the range and severity of baseline symptoms, comparisons between conditions are further limited by small Ns in many rarer conditions, resulting in low power to detect potential associations. In light of the rapidly expanding range of conditions, psychedelic treatments are being trialled for, it is nevertheless reassuring that no indication showed a trend towards increased negative consequences, providing preliminary evidence of psychedelics safety in these conditions. Younger age was related to both higher number and longer duration of negative outcomes. Previously, younger age has been found associated with increased unpleasant or challenging experiences with psychedelicsas well as higher rate of incidents leading to emergency medical treatment seeking following psychedelic use. A recent survey study found a correlation between younger age and problematic psychedelic use, which became non-significant after adjusting for variables related to patterns of use (of which higher frequency of use and social/recreational intentions were linked to problematic use; St Arnaud and Sharpe, 2022). The findings may indicate younger age to be associated with 'riskier' patterns of psychedelic use, that at least partially mediate associations with increased adverse effects. No correlation was observed between age and scores on the 17-item treatment outcome scale, suggesting equal overall treatment benefits across age groups. This study has several important limitations. First, self-selective sampling may disproportionately reach and attract certain characteristics. Our sample was predominantly white, young and educated, and although this appears to partly reflect the common demographic profile of psychedelic users, GDS may also disproportionately reach these populations. Low representation of ethnic minorities and socioeconomically disadvantaged individuals is a significant problem in psychedelic research, especially considering these populations are greatly affected by the mental conditions that any future psychedelic therapy would be used to treat; and recent evidence does suggest the psychedelic user population is becoming increasingly ethnically diverse. Furthermore, those reached by the survey advertising and who choose to volunteer may have specific interests and knowledge about the topics of the survey; and for instance be better educated about optimal practices of psychedelic use, contributing to more favourable outcomes. Retrospective self-reports are vulnerable to recall biases, and personal opinions and attempts to influence survey results may also affect responses. We note that as our survey covers the use of a wide range of substances and is advertised on platforms not directly related to psychedelic use, influence of both response and selection biases may be attenuated in our survey, compared to surveys exclusively focussed on psychedelic use which observe highly favourable attitudes towards psychedelics among respondents. Regardless, even if a representative sample of psychedelic self-treaters was obtained, these individuals likely hold positive expectations about the treatment; while resuming or discontinuing psychedelic use based on experiences before the survey reporting period induces an effect comparable to attrition or survivorship bias. Expectancy effects and volunteer biases are also issues in clinical trials across fields, but are particularly pronounced in psychedelic research due to the prevailing 'hype' around these treatments, and the strong effect of expectations observed particularly in responses to psychedelics. Nonetheless, if some experienced users had observed the majority of psychedelics' benefits during use before the survey reporting period, some of these effects may be attenuated in our study. The non-randomised, observational nature of the investigation also affects the assessment of the predictive value of some variables; as each respondent has, for instance, been able to choose the dose they consider most suitable for themselves. Crucially, respondents were asked to report on their experiences with the psychedelic they had found most useful in case they had self-treated with many. These effects could result both in more favourable outcomes overall, and more equal outcomes between substances and between intensities, than what might be observed in a randomised experiment. That generally favourable outcomes were observed across predictors does not necessarily indicate those predictors matter little, but rather that different things may work for different individuals. The administered outcome measurements also have limitations. Although our 17-item outcome scale demonstrated high internal consistency, the assumptions of Cronbach's alpha are often violated and other tests would ideally be run to for instance examine the factor loadings of each item. Furthermore, baseline levels of morbidity across items remain unknown; as discussed previously, this may particularly bias outcome comparisons between conditions, favouring conditions with higher range and severity of impairment. Furthermore, no validated symptom scales were used, limiting comparison of results to existing research. However, the use of such scales would have been impractical given the wide range of conditions investigated; and we also highlight the relevance of measuring broader aspects of wellbeing and functioning beyond symptoms attributed to a specific condition, which has been emphasised in modern mental health research. Regarding duration of outcomes, given our survey enquired about past-year experiences, the prevalence of longerlasting effects may have been underestimated in cases where respondents have experienced sustained outcomes at the time of reporting, but with not enough time having passed since the experience to report longer durations. We also did not record duration of outcomes for each item separately. The variance explained by our regression models was small. Responses to psychedelics have generally been found difficult to predict; yet, there were several unmeasured variables of interest with potential relationship to outcomes such as the presence and quality of interpersonal support before, during and after the experience; expectations; as well as mental state and certain personality characteristics. These and other unknown variables may have also acted as hidden confounders in our regression analyses. Finally, we cannot confirm the purity of substances used, and did not enquire about the dose used for self-treatment nor about potential other drugs or medications used concomitantly. To summarise, this study sheds light on individual selfadministered therapeutic use of LSD and psilocybin mushrooms, a practice which appears to be increasing but is little researched. We utilised a large, global sample, representing a diverse range of target conditions and problems. Self-treatment outcomes were generally favourable, with benefits observed across a wide range of outcomes and indications. Intensity of experience was among the strongest predictors of positive outcomes, being associated with not only stronger but also longer-lasting treatment effects. Persisting negative outcomes were relatively uncommon but appear more frequent than in clinical settings. Our findings can contribute to harm reduction efforts, as well as inform experimental research about potential risks, benefits and underlying therapeutic mechanisms of psychedelics. Future research can be improved with inclusion of additional predictor variables of interest, and utilisation of prospective designs including measurement of baseline symptoms.
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