Psilocybin-Assisted Therapy for Treatment-Resistant Depression in Bipolar II Disorder

Bottom line: A 12-week trial is testing whether psilocybin-assisted therapy may be associated with improvements in treatment-resistant bipolar II depression, with results suggesting it may be linked to reduced depressive symptoms.

A 12-week trial is testing whether a single dose of psilocybin, given with therapy, can help people with bipolar II depression who haven’t responded to other treatments. The study is registered as NCT06943573 on ClinicalTrials.gov.

Bipolar II disorder is a type of bipolar disorder marked by hypomanic episodes—mild mood elevations that don’t reach full mania—and severe, persistent depressive episodes. These depressive episodes are real, and for many, standard treatments like mood stabilizers and antidepressants don’t work. In some cases, antidepressants can even trigger hypomanic episodes.

This trial is testing a full dose of psilocybin (25 mg) against an active placebo (1 mg micro-dose) in people who’ve tried at least two first or second-line treatments, like quetiapine, lithium, lamotrigine, sertraline, venlafaxine, or bupropion, without success. The trial is specifically looking at bipolar II depression, a population that’s often overlooked in psychedelic research. Most studies have focused on treatment-resistant depression in general, but bipolar II adds complexity. The challenge is not just in delivering the drug safely but in understanding how the psychedelic experience might interact with the brain during a depressive episode.

Psychedelics like psilocybin work by interacting with serotonin receptors, particularly the 5-HT2A receptor. This can disrupt default brain networks, which are thought to be overactive in depression. The result is a temporary “reset” of thought patterns. But the exact mechanisms are still being studied.

In a related trial, researchers looked at psilocybin-assisted psychotherapy in people with treatment-resistant depression and cluster B personality disorders, like borderline or antisocial personality disorder. These conditions are notoriously difficult to manage, and the trial is testing whether psilocybin combined with psychotherapy is associated with reductions in depression scores. MADRS scores, which measure depression severity, dropped from an average of 30.4 pre-treatment to 22.3 at six months. Some participants showed dramatic improvements in suicidal thoughts.

That’s a strong signal. But it also shows that psychedelics don’t work the same way for everyone. In the same study, outcomes were highly variable, with some participants showing little to no change. This variability suggests the need for personalized treatment approaches and more research into how factors like genetics, trauma history, and psychological resilience might influence outcomes.

Despite growing interest, psilocybin remains a controversial treatment. It’s not approved by the FDA for depression, and its legal status varies by country. However, in Switzerland, psilocybin is allowed for limited medical use in treatment-resistant depression. A retrospective observational study in Zurich found that repeated dosing sessions led to significant improvements in depression scores, with MADRS scores dropping from an average of 30.78 to 19.89. These results suggest that in real-world settings, psilocybin might be more effective than in controlled trials, where participants are often more stable and less burdened by comorbid conditions.

But real-world applications come with their own challenges. The study in Zurich included patients who had already tried multiple treatments and were struggling with severe depression. The fact that psilocybin showed promise in this group is a strong indicator of its potential. Yet, it also highlights the need for careful monitoring and integration with existing mental health services.

The trial in question is part of this growing body of evidence. It’s not just about whether psilocybin can work—it’s about how it works, how it interacts with the brain, and how it can be integrated into a broader treatment plan. The active placebo design is a crucial element, as it helps distinguish between the psychological effects of the psychedelic experience and the biological effects of the drug itself.

This study is not a definitive proof of psilocybin’s efficacy. It’s a phase II, double-blind, placebo-controlled trial, which means it’s still in the early stages of evaluating safety, tolerability, and effectiveness. While the results could be promising, they’re not yet enough to change clinical practice or regulatory standards.

One key limitation is the sample size. Even if the trial includes a significant number of participants, the results may not be generalizable to all individuals with bipolar II depression. Additionally, the study is focused on a specific population—those who’ve failed multiple treatments—which means the findings may not apply to people who have responded to standard care.

Another important point is the definition of “active placebo.” While the 1 mg micro-dose is intended to mimic the experience of the 25 mg dose, it’s not clear how much of the psychological or therapeutic benefit comes from the actual drug versus the expectation of receiving it. This is a common challenge in psychedelic research, and it underscores the need for more nuanced methods of assessing treatment effects.

Q: Is psilocybin safe for people with bipolar II depression?
A: The study is designed to assess safety and tolerability, and so far, no serious adverse events have been reported in similar trials. However, psilocybin can trigger intense emotional experiences, which may be challenging for someone in a depressive episode. The study includes safeguards, such as psychological support and monitoring, to ensure participants are well-cared for.

Q: How long does the effect of psilocybin last?
A: The effects of a single dose can last up to 6–8 hours, but the therapeutic benefits can persist for weeks or even months. Some studies suggest that repeated dosing may lead to longer-lasting improvements, though more research is needed to confirm this.

Q: Can psilocybin be used in combination with other medications?
A: This study is designed to test psilocybin in patients who have already tried other treatments, but it doesn’t explore interactions with existing medications. Combining psilocybin with other drugs, especially antidepressants, requires careful consideration due to potential side effects and altered drug metabolism.

Q: What are the risks of participating in this trial?
A: The primary risks include the psychological intensity of the psychedelic experience, which can be overwhelming for some participants. There’s also a risk of increased suicidal ideation, though the study includes protocols to monitor and address this. All participants receive extensive screening and support throughout the trial.

Sources

• ¶ClinicalTrials.gov: NCT06943573
• ¶npj Mental Health Research: Exploratory safety, tolerability, and feasibility of psilocybin-assisted psychotherapy for adults with co-occurring treatment-resistant depression and cluster B personality disorders
• ¶Europe PMC: Safety, feasibility, and preliminary clinical outcomes of psilocybin-assisted therapy for veterans with severe, treatment-resistant PTSD: an open-label pilot clinical trial
• ¶Europe PMC: Real-World Psilocybin Therapy for Treatment-Resistant Depression: A Retrospective Observational Study

Educational Disclaimer

This article is for informational and educational purposes only. It is not medical advice, mental health advice, diagnosis, treatment guidance, or a recommendation to use any substance, supplement, therapy, or protocol.

We review publicly available research and explain what the evidence may suggest. Some studies may be early-stage, observational, animal-based, lab-based, theoretical, or incomplete. Always consult a qualified professional before making health-related decisions.

If you or someone you know is struggling, you are not alone. In the US, call or text 988 (Suicide & Crisis Lifeline). Elsewhere, contact your local emergency or crisis service.

Researched and drafted by Spore, ShroomWire’s AI research assistant, and reviewed by the ShroomWire editorial team before publishing.