Evaluating the Risk of Psilocybin for the Treatment of Bipolar Depression: A Systematic Review of Published Case Studies

Bipolar disorder carries a high burden of morbidity, including elevated suicide risk, impaired functioning, and particularly severe depressive episodes that are difficult to treat with current pharmacotherapies. Psilocybin has emerged as a promising novel antidepressant and has received Breakthrough Therapy designation for depression, but modern clinical trials have excluded individuals with bipolar disorder or a family history of bipolar disorder because of concerns that serotonergic psychedelics could precipitate mania or worsen illness course. Gard and colleagues set out to evaluate the empirical basis for those exclusions by systematically reviewing published case reports of adverse events associated with classic serotonergic psychedelics. The review focused on cases in which psychedelic use was followed by persistent manic or manic-like behaviour beyond the acute intoxication period, with an emphasis on assessing the risk that psilocybin (and related tryptamine psychedelics) may activate a manic episode in people with bipolar spectrum illness.

The investigators conducted a systematic search of PubMed, Web of Science, and PsychInfo for case reports published through 31 December 2020. Initial searches targeted psilocybin and hallucinogenic mushrooms using terms for case studies and case reports, and were expanded to include other classic psychedelics (LSD, ayahuasca, and DMT) when the psilocybin-specific yield proved small. Reported database yields included an expanded search of PubMed=255, Web of Science=134, and PsycInfo=152 prior to de-duplication and screening. Inclusion criteria required English-language reports (or translations) with at least an abstract or DOI, clear evidence that the individual had taken a psychedelic, and persistent adverse effects that could be interpreted as mania or psychosis with manic features lasting at least four days, requiring hospitalisation, or being clearly severe. Cases were included where the report described a pre-existing bipolar diagnosis, a history suggesting bipolar disorder, or persistent symptoms consistent with mania (for example decreased need for sleep or increased goal-directed activity). Reports solely describing transient intoxication, isolated psychotic episodes without mania, or Hallucinogen Persisting Perception Disorder (HPPD) were excluded. The reviewers did not exclude cases with polysubstance use but recorded such involvement. Two authors independently screened records and assessed possible cases for DSM-consistent manic behaviour; four authors conferred to resolve ambiguous cases. After initial screening yielded 43 candidate cases meeting basic inclusion criteria, 28 were excluded for failing the persistence or diagnostic criteria, leaving 15 published cases for detailed review. The authors extracted case characteristics and themes including prior bipolar history, family history, polysubstance use, and patterns of psychedelic dosing (single versus repeated exposures).

Fifteen published case reports met the study criteria; four of these involved psilocybin or psilocybin-containing mushrooms. Across the 15 cases the reviewers identified recurring themes: five cases included either a prior history of mania/hypomania or a family history suggestive of bipolar disorder, five reported concurrent substance use during the adverse event, seven had a history of substance misuse, and eight involved repeated psychedelic use over a relatively short period. Duration of adverse events varied from a few days to several months, with most reports indicating symptom resolution within days to weeks, although concurrent treatments confounded trajectories in many reports. Only two cases (Cases 11 and 13) involved individuals with a likely prior bipolar diagnosis. Case 13 described a psychiatrist with bipolar I who self-administered daily vaporised DMT (1 g daily for six months) in combination with phenelzine (60 mg daily) and was hospitalised for mania; the report did not allow disentangling the effects of chronic DMT, MAOI interaction, or other factors. Case 11 described a 30-year-old man who developed mania with delusions and hallucinations two days after a four-day ayahuasca retreat; he had exhibited hypomanic symptoms two weeks before the retreat. Three cases involved individuals without a documented bipolar history who developed sustained manic or manic-like syndromes after a single psychedelic ingestion and without clear recent polysubstance history. Case 6 was a 31-year-old man who took LSD once and presented two weeks later with decreased sleep, religious preoccupations, and an incident of breaking into a neighbour's home before hospitalisation and successful lithium treatment. Case 7 described a 21-year-old woman who developed persistent manic and psychotic symptoms one week after taking LSD at a music festival; she had a family history of bipolar disorder and schizophrenia. Case 2 involved a 22-year-old man who, after taking LSD, developed paranoid delusions culminating in homicidal behaviour and was hospitalised for four months. Most reviewed reports (12 of 15) described recreational use rather than formally supervised or clinical administration; three cases arose from guided retreats or self-directed treatment attempts. The authors did not find published cases in which an individual with a prior bipolar-spectrum diagnosis took a psychedelic and subsequently died by accident or suicide that could be clearly linked to induction or worsening of bipolar disorder.

Gard and colleagues interpret the case literature as indicating that psychedelic use can contribute to the onset of mania in some individuals, but that published reports are relatively scarce. The review identified 15 cases suggestive of mania or psychosis with manic features after psychedelic exposure; only a minority involved psilocybin specifically (n=4), and none of the clear single-exposure, non-polysubstance cases that produced sustained mania involved psilocybin-containing mushrooms. Concomitant risk factors that emerged from the cases included prior personal or family history of bipolarity, polysubstance use, and repeated dosing within short intervals. The authors place these findings alongside epidemiological research and the fact that modern clinical trials systematically exclude people with bipolar disorder, noting that population-level studies have not shown psychedelic use to be an independent predictor of later mania or psychosis. They therefore conclude that the small number of published case reports does not amount to overwhelming evidence of high risk, but emphasise that current knowledge is limited and cannot provide incidence estimates. Several limitations are acknowledged. The review is constrained to cases clinicians and researchers chose to publish, and so is subject to publication bias; case reports frequently lack detailed timelines, objective confirmation of substances or doses, and extended follow-up. Approximately half of the included cases involved concurrent or recent polysubstance use, making causal attribution difficult. The authors also note their focus on persistent adverse events excluded cases where patients died during acute intoxication, which might have involved undiagnosed bipolar spectrum disorders but where no definitive link can be drawn. Given these uncertainties, the investigators advocate for carefully designed prospective research to quantify risks and benefits for people with bipolar depression. They outline features for such trials including optimised set and setting, screening for risk factors (for example substance misuse and history of psychosis), conservative dose-escalation protocols, initial inclusion of participants without a history of mania (for example bipolar II) and older than the typical age of first mania onset (>30 years), and requirements for community and psychological supports after dosing.

This systematic review of published case reports identified a small number of instances in which classic psychedelics were followed by persistent manic or manic-like syndromes, but such reports are uncommon in the literature. Gard and colleagues conclude that while there is evidence of a possible risk of mania activation, the frequency of that outcome appears relatively low based on published case studies and available epidemiological data. They recommend cautious, prospective clinical investigation of psilocybin for bipolar depression under tightly controlled conditions that emphasise screening, set and setting, conservative dosing, and extended follow-up.