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

Bipolar II disorder (BD-II) is often associated with chronic and treatment resistant major depressive episodes. Psilocybin has shown promise for its rapid-acting antidepressant effects, though its impact on bipolar depression remains unexplored. In the present subgroup analysis of an already published trial on treatment-resistant depression (TRD), we aimed to preliminarily evaluate the safety and efficacy of psilocybin in patients with BD-II.

Adults with TRD associated with BD-II, excluding those with psychosis were included. Participants underwent one or two psilocybin sessions, each with a dose of 25 mg, along with preparatory and integrative psychotherapy sessions.

A total of four participants with a mean age of 37.5  ±  4.15 years were included. At baseline, the mean Montgomery-Åsberg Depression Rating Scale (MADRS) score was 32.5 (95% CI: 26.3-38.7, SD = 3.87). By week 2 post-dose, mean MADRS decreased to 20.3, and 2 weeks after dose 2, it further dropped to 19. At the end of the 6-month study, the mean MADRS score was 21.3. Young Mania Rating Scale scores remained stable at a mean of one throughout the study with no evidence of treatment emergent mania, hypomania or psychosis observed in any participants.

These findings suggest potential improvement in depressive symptoms with psilocybin administration in BD-II. Future studies with larger sample size are required to replicate our results and further evaluate antidepressant effects of psilocybin in bipolar depression.