Psilocybin and Bipolar Depression: Promise and Prudence

Abstract

Bipolar disorder affects approximately 40 million individuals worldwide, with depression being the most prominent phase of the illness. Owing to limited treatment options, bipolar depression remains a major public health concern, often causing significant functional impairment and increased suicide risk. Current therapies frequently lack rapid effectiveness, highlighting the need for novel approaches. Psilocybin, a psychedelic compound receiving growing interest for its potential rapid antidepressant effects, is under investigation in clinical trials combined with psychotherapy. Early studies in bipolar II disorder (n = 19) show encouraging results, but evidence is still limited, and important safety concerns such as affective switching and pharmacokinetic interactions persist. Additional challenges include regulatory restrictions, infrastructure demands, and uncertainties about the role of the psychedelic experience, especially given possible interference by common bipolar medications. Cautious, rigorous research is essential to determine psilocybin’s safety, efficacy, and practical application in bipolar depression, particularly for bipolar I disorder and long-term outcomes.

1. Introduction:

Depression represents a significant public health concern, affecting patients, their families, and communities. The disease's relapsing-remitting nature, the persistence of subsyndromal symptoms, and the lack of response to antidepressants in more than one-third of patients underscore the urgent need for rapid-acting antidepressants[1]. When considering novel therapeutic options in psychiatric care, few areas are in greater need of effective treatment alternatives than bipolar depression[2]. Bipolar disorder has a lifetime prevalence estimated at 2.5% in men and 2.3% in women[3], while the 12-month prevalence is estimated at 0.4% for bipolar I disorder, 0.3% for bipolar II disorder, and 0.8% for bipolar spectrum[4]. It is associated with significant functional impairment, reduced life expectancy, and a markedly elevated suicide risk, estimated to be 20 to 30 times higher than in general population[5]. During the course of illness, individuals with bipolar disorder spend significantly more time in depressive episodes than mania or hypomania. Moreover, subsyndromal depressive symptoms are both more pervasive and have longer duration than subsyndromal hypomanic or manic symptoms[6]. While the significant burden of bipolar depression highlights the necessity for developing new treatment options[7], research involving treatment for bipolar depression faces unique challenges, particularly the risk of affective switching[8].

The emergence of ketamine as a rapid-acting antidepressant (RAAD) and the approval by regulatory agencies of its s-enantiomer (esketamine) has renewed interest in investigating other dissociative and psychedelic compounds, such as psilocybin, for treating depression and other psychiatric disorders. Psilocybin in particular has garnered significant interest within both the academic community and the broader public due to its effects on consciousness, perception, mood, and thought processes[9]. This growing attention has resulted in an increasing number of studies evaluating its potential role in psychiatric disorders. Most clinical trials with psilocybin pair it with a psychological component and is often known as Psilocybin-Assisted Psychotherapy (PAP) or Psilocybin-Assisted Therapy (PAT). As of July 2025, 148 ongoing clinical trials, investigating psilocybin’s efficacy for various psychiatric conditions, were registered at ClinicalTrials.gov. While not yet approved for any psychiatric disorder by major agencies such as the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA), initial short-term studies show promising results for treating Major Depressive Disorder (MDD)[10-14]. However, methodological considerations such as generalizability, blinding integrity, the effects of concurrent serotonergic drugs, the need of long-term safety data, and the significance of psychological interventions continue to be subjects of ongoing discussion[15]. The scientific community maintains a cautious approach towards the broader translation of psilocybin research while navigating complex regulatory landscapes.

Only two clinical trials with psilocybin for bipolar depression, including both controlled[16] and open-label[17] studies, have been published (Table 1), with four others yet to be completed (Table 2). Given the inherent complexities associated with conducting research in bipolar depression, a rigorous discussion of the existing data and formulated hypothesis is paramount to guide future research and maximize its potential to give us the answers we need. This perspective aims to provide insights into the efficacy and safety data available and identify challenges pertinent to the potential clinical application of psilocybin for this population.

Table 1:

Published psilocybin trials in Bipolar II Disorder

First Author, Year	Study design	Time frame	Population (n)	Psilocybin dosage	Psychotherapy
Rosenblat, 2024[16]	Randomized with waitlist control trial	November 1, 2021, to February 1, 2023	Treatment resistant bipolar II depression (n=4)	Single 25 mg dose; possibility of up to two additional doses if relapse after primary endpoint.	One pretreatment session (1–2 hours), one dosing session (6–8 hours), and two posttreatment sessions (1–2 hours each)
Aaronson, 2024[17]	Single-arm, open-label clinical trial	April 14, 2021, to January 5, 2023	Treatment resistant Bipolar II depression (n=15)	Single 25 mg dose	Three pretreatment sessions (at least 3 h total), one dosing session, three posttreatment sessions (1 h each)

Table 2:

Registered ongoing psilocybin trials including patients diagnosed with Bipolar II Disorder

Study Title	Study Start	Location	Study Design	Population	Psilocybin Dose	ID
Psilocybin Therapy for Depression in Bipolar II Disorder (BAP)	January 2022	San Francisco, California, USA	Single-arm, open-label clinical trial	BDII, depressed, at least one failed medication trial	10–25 mg, up to two doses	NCT05065294
Neurobiological Effects of Psilocybin in Treatment Resistant Bipolar Depression (Psilo-BD)	October 2024	Toronto, Ontario, Canada	Single-arm, open-label clinical trial	BDII, depressed, at least two failed trials	25 mg, once	NCT06506019
Acceptability and Safety of Two Sequential Doses of Psilocybin in Bipolar Disorder II Depression and Suicidality	July 2025	Houston, Texas, USA	Single-arm, open-label clinical trial	BDII, depressed, with suicidality without active intent or plan	25 mg, up to two doses	NCT06706232
Psilocybin-Assisted Therapy for Treatment-Resistant Depression in Bipolar II Disorder (PAT-BD-01)	October 2025 (estimated)	Vancouver, British Columbia, Canada	Randomized, double-blind, placebo-controlled, parallel-group trial	BDII, depressed, at least two failed trials	25 mg, once	NCT06943573

2. Antidepressant Effect in Patients with Bipolar Disorder

2.1. Mechanism of antidepressant effect

Following oral ingestion, psilocybin undergoes rapid dephosphorylation to its active metabolite, psilocin. The pharmacological effects of psilocin seem to vary between individuals, influenced by factors such as prior exposure, physiological tolerance, and body mass index[18]. The onset of subjective effects is typically observed within 10-40 minutes post-administration, with peak intensity occurring between 60 and 90 minutes[18, 19]. Psilocin metabolites are primarily eliminated via renal excretion, with a reported mean elimination half-life of approximately 3 hours[18]. The primary antidepressant mechanism of action of psilocin is believed to involve the modulation of serotonergic neurotransmission, supported by its interaction with multiple serotonin receptor subtypes, with a notable affinity for the 5-HT2A receptor. Modulation of this receptor is thought to trigger a cascade of downstream effects, including increased glutamatergic neurotransmission and the promotion of neuroplasticity[18-21]. Furthermore, functional neuroimaging studies have demonstrated that psilocybin administration is associated with increased metabolic activity in key brain regions, such as the frontolateral, frontomedial, anterior cingulate, and temporomedial cortices[19, 20].

2.2. Published clinical trials in bipolar disorder

Two published feasibility studies have investigated psilocybin administration in individuals with bipolar depression. Rosenblat et al.[16] conducted a randomized controlled trial investigating feasibility and antidepressant response of PAP in treatment-resistant depression, where four out of 31 participants had a diagnosis of bipolar II disorder. Of note, participants were not permitted to continue antipsychotic medications, with the authors describing concern that 5HT2A receptor antagonism by these agents could impact psilocybin’s action in the receptor [16]. However, conventional mood stabilizers, that were not specified, were permitted at the discretion of prescribing physician and principal investigator’s clinical judgement. Participants received one, two or three doses of 25 mg of psilocybin over the span of six months of follow-up. For each dose, psychotherapy was provided during the dosing session (6–8 h) and approximately a total of 4.5 hours of therapy outside of the dosing session. Results involving the four patients with bipolar II disorder were recently published[22], showing a trend of decrease in Montgomery–Åsberg Depression Rating Scale (MADRS) score although no placebo group for comparison is available.

Aaronson et al.[17] conducted an open-label clinical trial that included 15 participants with bipolar II disorder, current depressive episode lasting at least for three months, and no remission after at least two pharmacological treatments. Psychotropics including mood stabilizers were discontinued at least two weeks prior to the administration of psilocybin. The dosing day consisted of 25 mg of psilocybin in addition to psychological support during the session. Participants also had three one-hour integration sessions with the lead therapist, which happened one day, one week and two weeks following the dosing session. After three weeks of dosing (primary endpoint), all participants had a reduction of MADRS score (mean change −24.00, 95% CI, −29.11 to −18.89; P < .001), 12 (80%) participants met the remission criterion (MADRS score ≤10) and one met only the response criterion (decrease in MADRS score of 50% or more from baseline). After 12 weeks (study endpoint), 12 of the 15 patients (80%) met criteria for remission based on MADRS.

Both studies exclusively included patients with bipolar II disorder; to date, there is no published evidence on psilocybin treatment in bipolar I disorder. Given the absence of randomized controlled data, including a placebo group with psychotherapy for comparison, the efficacy of psilocybin in treating bipolar depression is still far from being established. Feasibility data is promising and warrants further investigation into psilocybin’s antidepressant properties in bipolar depression. Both trials studied interventions involving 25 mg of psilocybin in addition to psychological support; the effects of microdosing have not been systematically studied in this population.

3. Safety Profile and Risk Assessment

3.1. Risk of Affective Switching

The incidence of treatment-emergent affective switching in individuals with bipolar disorder following the use of conventional monoaminergic antidepressants is substantial, with reported rates varying across study designs. In a 2018 systematic review including 51 studies and a total of 10,098 individuals with bipolar disorder, the pooled prevalence of treatment-emergent mania was 18.8%, with variation depending on study design. Specifically, cross-sectional studies (n = 4; 2,086 individuals) reported a pooled prevalence of 30.9%, prospective studies (n = 12; 1,929 individuals) reported 14.4%, and randomized controlled trials (n = 20; 1,316 individuals) reported 11.8%. [23]. In the Rosenblat et al[16] study, no mania or hypomania was observed among participants with bipolar II disorder who were followed for six months. In the study by Aaronson et al.[17], no manic symptoms were observed at the study endpoint (12 weeks), despite the absence of concomitant mood stabilizer use. However, these findings cannot be generalized to individuals with bipolar I disorder; this population is at higher risk due to their greater vulnerability to antidepressant-induced affective switching and the potential for more severe consequences during manic episodes[24].

Using less rigorous methodologies, efforts have been made to evaluate the risk of mood switching with psilocybin in individuals with bipolar disorder. In a study by Morton et al.[25], 541 participants with self-reported bipolar disorder and prior psilocybin use (excluding microdosing) completed a web-based survey; 14.2% reported experiencing manic symptoms within two weeks of use. However, the lack of diagnostic confirmation and reliance on unstructured, retrospective symptom reporting limit the validity of this study. A group of 15 participants from this survey were later interviewed for a qualitative analysis after diagnosis confirmation, published by DellaCrosse et al.[26], where they described that onset of mania following ingestion may have been impacted by concomitant use of other substances and sleep deprivation preceding the exposure. Meyer et al.[27] conducted a different retrospective study with greater internal validity, though with a smaller sample size (66 participants reported use of psilocybin), which did not exclude microdosing. Bipolar diagnoses were confirmed through structured interviews, and symptom data were gathered via semi-structured interviews covering the month before and the three months following psilocybin use. No significant difference was observed in the number of days with manic symptoms or psychosis before versus after use.

Several case reports have described symptoms concerning for mania and/or psychosis secondary to use of psilocybin and other psychedelics. In the majority of such reports, however, the differentiation between psychosis and mania with psychotic features is not clear[28-32], as highlighted by other literature reviews[33, 34]. Case reports involving psilocybin use did not describe a preestablished diagnosis of bipolar disorder. Only case report, by Hendin et al.[35], describes a characteristic manic episode following psilocybin ingestion without concomitant use of other substances. In that report, the patient had a strong family history of bipolar disorder (albeit no personal history), the amount of psilocybin consumed was not described, and was not being prescribed an antidepressant at the time of the episode. In the months following hospitalization, the patient experienced a second episode while on lamotrigine which was not attributed by substance use.

Finally, we highlight am important limitation when interpreting findings from such retrospective surveys and case reports. Symptoms that present during mania or even prodromal phases, including impulsivity and risk-taking behaviors, could predispose individuals to psychedelic experimentation, similarly to what has been observed with the use of other substances[36]. Therefore, the emergence of manic symptoms following psychedelic exposure in this population may reflect the natural progression of an underlying mood disorder rather than a direct pharmacological effect, confounding estimates of psychedelic-induced mania through selection bias. This issue is particularly salient in studies where participant selection and diagnostic criteria are less stringently controlled[37]. Future rigorous clinical trials examining psilocybin's efficacy in bipolar depression will need to implement safeguards to mitigate this risk, including restrictive enrollment criteria requiring confirmed bipolar disorder diagnoses and comprehensive psychiatric screening to exclude individuals presenting with mixed affective states or other confounding clinical features.

3.2. Risk of Psychosis

Psychosis is a described adverse effect from exposure to psychedelics, including psilocybin, with incidence estimates varying significantly according to study methodology and population studied[38]. When considering specifically the risk associated with bipolar disorder, the two published clinical trials involving patients with BDII (total of 19 patients) did not observe the occurrence of psychotic symptoms. Furthermore, the previously described retrospective assessments again yielded different results. In the larger sample (N=541) presented by Morton et al.[25] 8% (n=45) of participants described experiencing hallucinations within 2 weeks of using psilocybin, and 7% (n=38) described delusional beliefs during that period. As diagnostic response options were not mutually exclusive, about 9% (n=49) of participants self-reported a history of psychotic disorder (which could represent conditions such as schizophrenia or mania with psychosis). On the other hand, patients that participated in the semi-structured interviews by Meyer et al.[27] did not present an increase in psychotic symptoms.

3.3. Impact on sleep

In the open-label trial from Aaronson et al.[17] that enrolled 15 patients with BDII diagnosis, moderate insomnia was an adverse effect observed in 2 participants (13%), with subacute onset (1 week and 4.5 weeks after dosing) and resolution before the end of the study (one participant required a medication to treat it). In the self-reported retrospective data (N=541) from Morton et al.[25], about 10% (n=56) of participants reported difficulties falling or staying asleep within 14 days of psilocybin use. However, incidence prior to exposure was unknown; the qualitative analysis DellaCrosse et al.[26] that followed after interview of 15 participants highlights that some participants’ sleep was already disrupted by the time of consumption, and some participants also reported improvement in sleep following administration. Considering the close link between sleep changes and mood instability during the course of bipolar illness[40], it is essential for future studies to closely monitor sleep patterns and register the observed changes.

3.4. Interactions with mood stabilizers and antipsychotics

Pharmacological interactions of psilocybin with medications prescribed for bipolar disorder are a significant concern and remain largely unexplored. This gap in knowledge is particularly evident in clinical trials, where participants with bipolar II disorder have been required to discontinue antipsychotic medications prior to enrollment. This exclusion is noteworthy given the widespread use of these medications in clinical practice, where nearly half of patients with bipolar II disorder, and more than two-thirds of those with bipolar I disorder, are prescribed an antipsychotic, most commonly a second-generation or atypical antipsychotic[41]. Commonly used atypical antipsychotics in bipolar depression, such as olanzapine, quetiapine, and lurasidone, are known 5-HT2A antagonists. Psilocybin, by contrast, acts as a partial agonist at the 5-HT2A receptor, a mechanism believed to underlie its psychoactive and potential therapeutic effects. There is evidence that 5-HT2A antagonists can attenuate the psychedelic experience[42, 43]; however, their impact on psilocybin’s antidepressant efficacy remains unknown.

Limited data is available on interactions involving psilocybin and mood stabilizers such as lithium or antiepileptics. A study[44]reviewing anonymous online reports from three websites (Erowid.org, Shroomery.org, and Reddit.com) found that a significant percentage of patients on lithium (29 of 62 reports) alongside psychedelics experienced seizures, whereas none of the 34 reports from patients on lamotrigine reported seizures. Notably, only six of the 62 reports of psychedelic use in individuals on lithium involved psilocybin. These anecdotal findings should be interpreted cautiously given the nature of the data but may point to new directions for researching the safe administration of psychedelics.

3.5. Interactions with monoaminergic antidepressants

Further investigation regarding interactions with monoaminergic antidepressants is also required. Despite concerns involving efficacy and risk of affective switching, such agents are prescribed for bipolar depression in rates close to 50% in outpatient settings[45]. Use of monoaminergic antidepressants may reduce psychedelic experience of psilocybin; however, preliminary evidence from small-scale studies suggests that this attenuation does not significantly compromise its therapeutic efficacy in treating depressive symptoms[43, 46]. This is aligned with the studies previously cited, where discontinuation of antidepressants prior to psilocybin use does not seem to have interfered with treatment efficacy, although such requirement may have impacted recruitment[47]. Other area of concern is safety involving the risk of serotonin toxicity when combining psychedelics with antidepressants or other serotoninergic medications[48]. Goodwin et. al.[49] investigated the combination of psilocybin and selective serotonin reuptake inhibitors in patients with treatment-resistant depression and reported a safety profile comparable to that of psilocybin monotherapy in other trials, while emphasizing the need for continued vigilance in future studies.

4. Implementation Challenges and Clinical Considerations

4.1. Regulatory and Legal Framework Challenges

Psilocybin presents unique regulatory barriers compared to other treatments for bipolar depression. While several interventions are used off label for bipolar depression with support from clinical evidence and professional guidelines, clinical use of psilocybin is mostly restricted worldwide, limiting such application. Still, there are noticeable differences between countries, which leads to unique challenges now and in the future. In Canada, psilocybin may be prescribed for treatment only through unique pathways such as its Special Access Program[50], which allows physicians to request unauthorized drugs when other treatments for serious conditions are unsuccessful. In the United States, a petition through a similar pathway (The Right to Try Act[51]) was recently denied[52] for a terminally ill, with unknown future implications in the country for patients and clinicians considering psilocybin in treatment-refractory cases. Some countries may allow the commercialization of products containing psilocybin, such as “magic truffles” in The Netherlands, although psilocybin is not available for clinical use[53]. Finally, Australia in 2023 enabled authorized psychiatrist to prescribe psilocybin for treatment resistant depression, with use for other conditions still being designated as schedule 9 (prohibited substance)[54]. Regulations also vary between states within the same country, complicating this landscape in certain jurisdictions. In the United States, for example, Oregon has licensed over 20 psilocybin service centers that operate outside traditional medical settings[55].

This regulatory barrier is particularly relevant given that we already observe a dramatic increase in unregulated psilocybin use outside clinical settings. According to Rockhill et al., prevalence of use in adults increased by an estimated 44% from 2019 to 2023, with psilocybin exposures reported to U.S. poison centers increasing by over 200% in adults and 300% in teenagers[56]. This trend is especially pronounced among individuals with moderate depressive symptoms. Depression has already been identified as a potential motivation for psilocybin use among patients with bipolar disorder. The growing media attention[57] and the possibility of future approval of psilocybin for TRD by other regulatory agencies (supported by recently announced positive results from phase-3 trial NCT05624268) may further encourage unsupervised use within this vulnerable population, either through available non-clinical settings (where this is an alternative) or unregulated routes.

4.2. Clinical Infrastructure and Treatment Delivery

The challenge of standardizing psilocybin treatment delivery is considerable given the complex infrastructure required for the treatment course in studies published so far[11-14, 16, 17]. To reduce the risk of adverse events, protocols have required comprehensive pre-treatment screening, including detailed psychiatric and medical assessment, review of concurrent medications, and, when indicated, laboratory or cardiovascular evaluation. Dosing days usually involve continuous on-site supervision for 6–8 hours with regular monitoring of vital signs, management of acute anxiety or disorientation, and documented clearance before discharge, often contingent on the presence of a responsible person for post-session transportation. Evidence so far also suggests that psychotherapy is not merely adjunctive but essential for treatment[58, 59], with protocols requiring appropriately trained psychotherapeutic personnel for preparation, dosing session, and integration phases over the span of weeks. However, some investigators have questioned the necessity of psychotherapy in conjunction with psilocybin[60] and have begun to move towards a psychoeducation and psychological support model[61], particularly following the FDA’s rejection of MDMA-assisted psychotherapy for Post-Traumatic Stress Disorder[62].

For patients with bipolar disorder, clinical infrastructure demands will be even greater. The risk of affective switching necessitates enhanced monitoring protocols extending beyond standard psychological support requirements. Early detection and intervention for emerging manic symptoms, such as changes in sleep, are critical and require close follow-up with clinicians with expertise in recognizing mood changes beyond the dosing sessions. As little is known regarding potential risk for affective switching in bipolar patients, frequency of such post-session monitoring for such purpose is yet to be determined. In addition, the higher prevalence of psychiatric comorbidities in this population[63], including substance use disorder and anxiety disorders, often results in polypharmacy and increases the potential for interactions that require careful assessment by expert clinicians[64, 65].

These complex requirements also bring concerns pertaining equity. With a hypothetical future approval of psilocybin for clinical use in bipolar depression, patients may face difficult choices between regulated medical treatment and more accessible, potentially less expensive non-clinical or even unregulated options. Individuals with bipolar disorders are at a greater risk of unemployment and overall financial struggles[66], which can limit access to more costly clinical settings offering care in the future. Given the substantial unknowns regarding psilocybin's effects in bipolar disorder, particularly the risk of mood switching, psychosis and interactions with other medications, administration without proper clinical monitoring introduces further uncertainty about treatment outcomes and patient safety in an already vulnerable population.

4.3. The need of psychedelic experience

The psychedelic experience is believed to be mediated by 5-HT2A receptor agonism, with greater intensity and breadth of subjective effects being correlated with higher doses of psilocybin[67, 68]. There is still an unresolved question on whether the presence of a psychedelic experience is necessary for therapeutic efficacy. This issue is particularly relevant in the context of bipolar disorder, where commonly prescribed second-generation antipsychotics may attenuate psychedelic effects through 5-HT2A antagonism[42, 43]. If a psychedelic experience was to be required, such attenuation may potentially require the use of higher doses to achieve the desired response, posing additional risks such as disruption of ongoing antipsychotic therapy, overdose, and other unknown consequences.

The ketamine literature offers an interesting parallel. Despite initial hypotheses that dissociative experiences were necessary for antidepressant effects, research so far has not supported this connection.[69-71] Still, the psychedelic experience differs qualitatively from ketamine-induced dissociation, and its role in treatment outcomes remains unclear. In secondary analysis of psilocybin studies, the mystical-type experience has been proposed as a predictor of antidepressant response[72, 73]. However, medication-induced attenuation of psychedelic effects has not compromised antidepressant response in animal models[74] and case report[43]. It is possible that ongoing research with “non-hallucinogenic psychedelics”[75], agents that would exert similar effects such as 5-HT2A activation without an associated hallucinogenic properties, may contribute to better understanding the role of a psychedelic experience in treatment. Ultimately, clinical trials targeting this question are still needed, particularly in patients with bipolar disorder.

5. Future Research

Given the limited available evidence regarding psilocybin’s efficacy and safety for bipolar depression, research will be paramount to address the many remaining questions. Four ongoing trials are currently investigating psilocybin use in bipolar depression (Table 2), though these still exclude participants with a diagnosis of BDI. Notably, this list includes the first randomized, double-blind, placebo-controlled (1 mg) trial in patients with BDII (NCT06943573), with estimated enrollment of 90 participants and expected completion by the end of 2028.

While the other three studies have an open-label, single-arm design, we can expect to learn more from their unique characteristics. The trial NCT05065294, with estimated enrollment of 14 participants, has already achieved primary completion. This study allows the administration of a variable psilocybin dose (10mg-25mg) as well as a second dosing session, which may reveal more about the effects of different regimens in patients with BDII. We can also anticipate the first trial (NCT06506019) investigating neurobiological effects of psilocybin in this population using fMRI (functional magnetic resonance imaging), with a particular interest in the association of post-treatment activity in the right amygdala and antidepressant effects. This study has an expected completion in 2027 and estimates enrollment of 30 participants. Finally, the trial NCT06706232 will be the first to study treatment specifically in participants experiencing suicidal ideation (without an active plan or intent), with one or two dosing sessions 4 weeks apart. The study is expected to enroll 10 participants and is to be completed by 2027.

Several challenges identified in this article remain unaddressed by ongoing studies and will need to be considered when designing future trials. We continue to have no efficacy or safety data on the use of psilocybin in participants with BDI. The effects and risks of different psilocybin regimens, including variation in dose and dose frequency, require further elucidation. Should adverse effects such as affective switching be confirmed, characterizing their incidence, time to onset, and severity would inform the development of monitoring protocols. Future research should also explore how psilocybin may interact with commonly prescribed agents in bipolar disorder, including potential changes in antidepressant effect, risk of affective switching, psychosis, sleep changes, and overall safety of combined use.

6. Conclusions

In summary, while psilocybin demonstrates considerable therapeutic potential, its application in bipolar depression remains in a nascent and exploratory phase. Published and ongoing trials mostly consist of small, open-label, single-arm studies focused primarily on safety and feasibility, with exclusion of participants with BDI. Furthermore, risks of affective switching and psychotic symptoms, along with the need for long-term data, regulatory clarification, and implementation solutions, underscore the many considerations that must be addressed before broader use in bipolar disorder.

Key Points.

1. Bipolar depression remains a major unmet clinical need, with limited treatment options and minimal data on novel therapies such as psilocybin, particularly in bipolar I disorder.

2. Early studies in bipolar II disorder suggest psilocybin may offer antidepressant benefits, but safety concerns such as affective switching and drug interactions require caution.

3. Regulatory restrictions, lack of long-term data, and the need for specialized clinical infrastructure limit psilocybin’s current applicability in bipolar depression.