On the Relationship between Classic Psychedelics and Suicidality: A Systematic Review

Earlier research on classic psychedelics (for example psilocybin, ayahuasca, and LSD) presents a mixed picture regarding their relationship with suicidality. Some epidemiological and case-based reports have suggested increased suicidal ideation or behaviour following use, while other studies — including more recent cohort work and clinical investigations of psychedelic therapy — have suggested potential protective or therapeutic effects. Heterogeneity in samples (adolescents versus nationally representative adults), varying control for confounders (such as other substance use and psychiatric history), and differences in context (recreational, ceremonial, or clinical) have contributed to these conflicting findings. To address this uncertainty, Zeifman and colleagues conducted a systematic review to synthesise available evidence on the association between classic psychedelics and suicidality. The review considered both non-clinical (recreational or ceremonial) psychedelic use and psychedelic therapy in clinical settings, with the aim of clarifying whether classic psychedelics are linked to increased suicide risk, decreased suicidality, or show no clear association, and to highlight gaps for future research. The authors frame the work as timely given rising lifetime use of psychedelics and ongoing interest in psychedelic therapy as a novel psychiatric intervention.

The systematic review followed PRISMA guidance and was registered on PROSPERO (CRD42020158443). The investigators searched MEDLINE, PsycINFO, and PubMed from inception to 28 March 2020, and repeated the search on 5 November 2020. Search terms combined psychedelic-related keywords (psychedelic*, hallucinogen*, psilocybin, ayahuasca, DMT, mescaline, peyote, LSD) with a broad set of clinical and symptom terms including suicid*. Reference lists of eligible papers and reviews were also checked. Eligibility included any study reporting on associations between classic psychedelics (non-clinical use or psychedelic therapy) and suicidality outcomes. Studies of microdosing or non-classic psychoactive compounds (for example ketamine, MDMA, cannabis, benzodiazepines) were excluded. No restrictions were placed on participant age, gender, psychiatric diagnosis, or year of publication. Screening and data extraction were performed in duplicate: two reviewers independently screened titles/abstracts and full texts, resolving disagreements by discussion with a third reviewer when needed. Extracted items included study design, sample characteristics, details of psychedelic exposure or intervention, suicidality measures and outcomes, and follow-up duration. The review team used the Oxford Centre for Evidence Based Medicine (OCEBM) Levels of Evidence to appraise methodological quality (levels 1–5, with 1 highest). The extracted text does not indicate that a quantitative meta-analysis was performed; data synthesis appears to be narrative, integrating findings across study designs.

The review synthesised heterogeneous evidence spanning non-clinical use, early (mid-20th century) clinical reports, and modern clinical trials and observational studies. Study designs varied widely and included longitudinal cohorts, cross-sectional surveys, case reports/series, and clinical trials; many early studies were retrospective and of limited methodological rigour. Non-clinical psychedelic use: Among prospective longitudinal work, five cohort studies were noted (all within the past five years), with two providing evidence consistent with a protective effect of lifetime psychedelic use on subsequent suicidality. Three prospective studies reported reductions in suicidal ideation following psychedelic use in ceremonial or observational clinical contexts, with reductions linked to decreased experiential avoidance in at least two studies. Of 17 cross-sectional studies, the extracted text reports that 10 found an association between psychedelic use and increased suicidal ideation/attempts, whereas eight reported either reduced suicidality or no clear association; the authors note that some discordant findings arise from analyses of the same national data sets but differing adjustment for confounders. The review identified 11 deaths deemed reasonably linked to non-clinical psychedelic use (methods reported included jumping from heights, drowning, self-stabbing and others), though the authors emphasise such events were rare and that intent or substance confirmation was often unclear. The narrative cautions that non-controlled settings where individuals are alone and have access to lethal means may pose particular risks. Early psychedelic therapy reports: Sixteen early studies (case reports, case series, and clinician surveys) were summarised. Most did not demonstrate a clear elevation in suicidality attributable to psychedelic therapy beyond the baseline risk in severely ill psychiatric patients; several case reports described improvements in chronic suicidality. The authors identified six deaths temporally linked to early clinical psychedelic administration. Two survey-derived crude suicide rates from historical clinician reports were presented: Malleson’s UK data yielded 0.7/1,000 patients (from approximately 4,300 patients), and Cohen’s US survey reported 0/1,000 in experimental subjects and 0.4/1,000 in patients (from roughly 5,000 subjects). The authors compare these figures to a global suicide rate of 11.4/100,000 and to a substantially higher rate among psychiatric patients after hospital discharge (484/100,000), noting limitations of these historical data. Modern psychedelic therapy trials: The review identified two randomised controlled trials and three open-label trials that reported suicidality outcomes, although none were designed primarily to test effects on suicidality and many excluded participants at serious suicide risk. A wait-list-controlled crossover trial of psilocybin in major depressive disorder (N = 25) showed no significant between-group reduction in suicidality before crossover, but a significant decrease post-crossover with a large effect size; the authors note this could reflect regression to the mean or insufficient power. Open-label psilocybin trials in treatment-resistant depression reported significant reductions in suicidality at 1 and 2 weeks post-treatment, with later timepoints showing reductions that did not survive correction for multiple comparisons. A small RCT of ayahuasca versus placebo (N = 29) did not find a statistically significant between-group reduction in suicidality, though medium between-group and large within-group effect sizes were reported at early timepoints (days 1, 2, and 7). An open-label ayahuasca study reported rapid (within 40 minutes) and sustained decreases in suicidality up to 21 days. Across these trials, reductions in suicidality were strongly correlated with reductions in non-suicidal depressive symptoms, suggesting overlapping mechanisms. Key limitations noted by the authors include small sample sizes, exclusion of individuals with high suicide risk (creating possible floor effects where baseline suicidality is low), short follow-up durations (no assessments beyond 6 months reported), and frequent reliance on a single suicidality item drawn from depression scales rather than dedicated suicidality measures. Safety and adverse events: Modern trials did not report adverse suicide-related events or marked escalations in suicidality attributable to psychedelic administration. The authors attribute improved safety reporting in contemporary research to stricter screening (exclusion of serious suicide risk, bipolar or psychotic disorders) and greater attention to therapeutic setting. Nonetheless, early trials documented suicide-related adverse events, and the reviewers recommend careful risk-management when treating individuals with elevated suicidality.

Zeifman and colleagues interpret the evidence as preliminary and mixed but cautiously encouraging regarding therapeutic potential. They conclude that psychedelic therapy may be associated with acute and sustained reductions in suicidality in some clinical populations, and that non-clinical classic psychedelic use in some contexts may be associated with reduced suicidality; conversely, unmonitored use in unsafe environments can, on rare occasions, be linked to fatal outcomes. The authors emphasise that these conclusions are tentative given the limitations of the literature: only a small number of prospective trials exist (they state three small randomised trials and four additional prospective open-label trials), most reports are retrospective case series or case reports, and many studies did not measure suicidality as a primary outcome or use standardised suicidality instruments. The reviewers highlight methodological issues that likely contribute to inconsistent findings, including failure to control for psychiatric confounders in some cross-sectional analyses, publication bias (a tendency to publish negative outcomes while positive recreational outcomes go unreported), and reliance on self-report data. They also discuss plausible mechanisms for both increased and decreased suicidality: acute harms might arise from transient executive dysfunction or challenging experiences in uncontrolled contexts, whereas reductions might stem from decreases in experiential avoidance, improvements in depressive symptoms, psychological insight or emotional breakthroughs, immunomodulatory effects, or neurobiological changes such as altered functional connectivity or neuroplasticity. The extracted text notes that mechanistic work remains very limited. For clinical practice and future research, the authors recommend cautious, staged investigation of psychedelic therapy in individuals with elevated suicidality. Suggested safeguards include integrating psychedelic interventions with established suicidality-focused psychotherapies (for example dialectical behaviour therapy or cognitive behavioural therapy for suicide prevention), implementing suicide risk management protocols, maintaining participants in controlled environments until acute risk subsides, ongoing safety monitoring between sessions, and considering inpatient or residential settings when appropriate. They propose initially excluding imminently suicidal individuals or those with recent life-threatening attempts, with the possibility of expanding inclusion criteria if accumulating safety data support such a step. Finally, the authors call for larger prospective cohort studies of non-clinical use, adequately powered randomised controlled trials that recruit participants with clinically significant suicidality, use of validated suicidality measures (for example the Scale for Suicide Ideation, implicit association tests for death/suicide, and clinician-administered tools such as the Columbia Suicide Severity Rating Scale), and mechanistic research to clarify how classic psychedelics might influence suicidality.