Reactions to psilocybin administered in a supportive environment

Safety and general outcomes: Across the full sample of 175 subjects, the authors reported no lasting physical effects and that all subjects were alive and healthy at follow‑up. Within available follow‑up data (reported for a six‑month period), no subjects were hospitalised or developed enduring psychotic or neurotic symptoms. The authors note one pregnant woman who took psilocybin repeatedly at roughly two‑week intervals and who, with obstetric approval, had no reported adverse outcomes for mother or child in the first year after delivery. The authors reported no evidence of addiction, withdrawal symptoms or prolonged hangovers; roughly 90% of subjects stated they wished to repeat the experience at some time, but the authors observed no signs of physical or psychological dependence. Questionnaire sample and dosing: The principal analyses used questionnaires returned by 98 subjects (73 men, 25 women) reporting on their initial psilocybin session. In that subsample the mean absolute dose was 18.1 mg (SD = 11.6); when controlled for body weight the mean was 0.26 mg/kg (SD = 0.15). The median dose for the overall 175‑subject study was reported as 16 mg, with an interquartile range of 12–20 mg and a total range of 4–100 mg; doses above 50 mg typically resulted from a second ingestion many hours after an initial dose. The experimenters had set a conservative safety limit of 0.5 mg/kg for a six‑to‑eight‑hour period. Primary descriptive findings: In the context of the reported “supportive” setting (78% of respondents rated the setting as supportive), most initial experiences were reported as positive. Reported proportions for the initial experience (n=98) included: 70% described pleasant or ecstatic experiences; 88% reported learning something or having insights; 62% said the experience changed their lives for the better; and 90% wished to repeat the experience. Seventy‑two per cent characterised their experience as primarily interpersonal rather than primarily personal; many sessions were group based, which the authors suggest influenced this result. Mean reported duration for major effects was 6.5 hours (SD = 9.8) and for minor effects 16.8 hours (SD = 25.9). Respondents indicated a mean of 2.9 hours (SD = 3.5) as the time someone should be present to help or accompany them during the experience. Associations with background variables: Prior experience with psychedelic or related drugs (self‑rated on a 1–5 scale) correlated positively with dose (r = .25), time taken to consume the drug (r = .25), length of major effects (r = .26), rated familiarity of the experience (r = .21) and pleasantness (r = .26). In short, more experienced users tended to take higher doses, spaced over time, reported longer effects and found the experience less alien and more pleasant. Self‑ratings of personal flexibility correlated with prior drug use and drinking and with longer major effects (r = .22) and greater familiarity to ordinary life (r = .19). Alcohol use showed modest correlations with dose (r = .19) and consumption time (r = .27) but not with the main drug‑effect variables. Situational effects: Group composition and atmosphere were strongly related to subjective outcome. Group size was analysed by thirds and by chi‑square; small groups tended to be seen as more supportive and slightly more pleasant (non‑significant trend), while moderate groups (six to eight people) were associated with greatest reported learning. The number of people actually taking the drug correlated positively with group size (r = .55) and negatively with perceived supportiveness (r = –.28), pleasantness (r = –.24), and amount of learning (r = –.25). Pre‑session apprehensiveness (rated 1–5) correlated positively with pleasantness (r = .33), with interpersonal quality of the experience (r = .23), and with desire to repeat, but negatively with perceived supportiveness (r = –.22). Perceived supportiveness correlated positively with pleasantness (r = .43), amount of learning (r = .28), positive life‑change and interpersonal aspects (r = .32). Larger groups and larger numbers taking the drug were also associated with an expressed desire for a medically trained psychiatrist to be present (group size r = .23; number taking drug r = .39). The authors summarise that small, supportive groups tended to produce the most pleasant and educational experiences, while larger groups tended to be experienced as rejecting and produced less positive outcomes. Dose effects and intercorrelations: Dose (controlled for body weight) correlated highly with reported duration of major effects (r = .71) and with time taken to consume the dose (r = .80). Dose correlated modestly with length of minor effects (r = .24), with amount of reported learning (r = .30) and with perceptual (vs abstract) quality of experience (r = .21). Pleasantness correlated with amount of knowledge gained (r = .41), positive life‑change (r = .24) and desire to repeat (r = .39). Amount learned correlated strongly with reported life‑change (r = .58), and modestly with dosage (r = .25), pleasantness and perceived supportiveness. The main determinant of perceptual versus abstract experience reported was dosage (higher doses producing more perceptual experiences, r = .21). Interpersonal versus personal experience: Experiences judged personal (self‑focused) were more likely in larger or perceived‑rejecting groups (correlations reported r ≈ .18–.32) and in subjects with greater pre‑drug apprehension (r = .23). Pleasantness and desire to repeat correlated negatively with personal experience (r = –.26 and –.23 respectively). In short, large, anxious groups tended to yield more personal and less pleasant reports; small, supportive groups tended to yield interpersonal, pleasant experiences. Attitudes to psychiatric oversight and antidote availability: Among the 98 respondents, 12% were opposed to the presence of a medically trained psychiatrist, 65% did not care, and 23% favoured such presence. Eighteen per cent said they would have been happier if an antidote had been available. Those favouring a psychiatrist tended to come from groups with many people taking the drug (r = .39), took smaller doses (r = –.26) and reported less learning (r = –.28). Multivariate and longitudinal analyses: A centroid factor analysis yielded four factors; the three interpreted by the authors were: Factor I, an intense positive educational experience cluster (possible halo effects of subjective ratings); Factor II, an unpleasant large‑group cluster; and Factor III, an intense small‑group experience cluster unrelated to pleasantness and more commonly found in women. A subsample of 35 subjects who completed a second session and questionnaire showed only one statistically significant mean difference: group size tended to be smaller at the second session. There was little consistency across individuals between first and second sessions on major dimensions such as pleasantness, amount learned and life‑change; however, perceptual versus abstract and interpersonal versus personal dimensions showed higher stability, particularly the interpersonal aspect. Predictors of second‑session pleasantness and learning included whether the first experience was conceptual versus perceptual, the amount learned in the first session (less learning the first time predicted greater benefit the second time), and the length of assistance required after the first session (more assistance predicted less favourable second experience). Predictors that the second session would be interpersonal included first‑session learning and life‑change (negative correlations reported for one variable) and the first‑session desire for a psychiatrist (positive correlation), which the authors interpret as evidence of divergent uses of the experience (interpersonal communication vs analytic self‑exploration). Qualitative illustrations: The paper includes selective free‑report excerpts illustrating positive interpersonal, mystical‑type, perceptual and negative (loneliness, nausea, anxiety) experiences, and one account illustrating high‑dose perceptual and disorganised phenomena. These excerpts are used by the authors to illustrate the range of responses and the influence of group atmosphere and dose.

The authors frame their conclusions as tentative and preliminary, emphasising methodological limitations. Principal limitations they acknowledge are reliance on retrospective self‑evaluation, the volunteer selection bias (subjects were self‑selected and likely to have a positive initial expectation or “set”), lack of systematic pre‑session measurement of expectation and personality, absence of formal control or placebo conditions, and that all sessions were run by the same investigative team in a single type of supportive, naturalistic setting. They note that these factors constrain the generalisability of the findings. Within those constraints, the authors conclude that when psilocybin is administered in a supportive environment and accompanied by a positive set, subjects tended to report experiences that were pleasant, educational and in many cases life‑changing. Group size and atmosphere were important determinants of outcome: small groups (under six) and perceived supportiveness were associated with greater pleasantness, more interpersonal experiences and greater reported learning, while large groups (more than eight) tended to be experienced as rejecting, more anxiety‑provoking and less pleasant. Dosage predicted duration of major effects and was moderately associated with amount of reported learning and with perceptual (versus abstract) quality of the experience. The authors report little individual consistency across first and second sessions on broad subjective dimensions, although some aspects (perceptual/abstract and interpersonal/personal) showed more stability and some first‑session features predicted the character of a subsequent session. The authors discuss possible mechanisms and account for differences between their findings and the psychiatric literature that emphasises psychotomimetic and dangerous effects. They attribute part of the divergence to selection (volunteer bias), preparation (informal pre‑session discussions fostering expectations of insight), setting (naturalistic, non‑structured environment) and heightened suggestibility under the drug, which would amplify environmental and interpersonal influences. The authors also note investigator attitudes and personality differences as potential determinants of response; they observed that a self‑rating of flexibility related to some outcome measures but acknowledge that formal personality assessment was not undertaken. Tentatively, the authors propose a psychological mechanism of diminished perceptual selection and inhibition under psilocybin, leading to increased suggestibility, altered perception and reports of insight; however they state that the present data do not enable resolution among competing theoretical accounts. Finally, the authors situate their findings relative to prior reports of largely pleasant and insightful outcomes from single psychedelic sessions, noting congruence with some earlier work, while reiterating that the present results are descriptive of what occurs under the specific supportive conditions studied and should not be taken as definitive about psilocybin effects in other settings or populations.