Acceptability & Safety of Two Sequential Doses of Psilocybin in Bipolar Disorder II Depression and Suicidality

Inclusion Criteria: * Must have completed written informed consent * Must be at 25 years of age or older at screening (but below age of 70) * Confirmed Diagnostic and Statistical Manual of Mental Disorders (DSM-5) diagnosis of BD-II using clinical records and Diagnostic Interview for Anxiety, Mood, and Obsessive-compulsive disorder (OCD) and Related Neuropsychiatric Disorders (DIAMOND) * Must meet criteria for suicidality according to the INQ cutoff scores: A score of at least 12 on the Perceived Burden (PB) subscale and at least a score of 36 on the Thwarted Belongingness (TB) subscale indicating substantial risk for passive suicidal ideation * Must meet criteria for depression according to the MADRS cutoff scores: A score of 7-34 indicating mild to moderate depression * Must pass medical examination (physical exam, personal/family medical history, including consultation with current medical provider, ECG, about 4 tablespoons blood draw, psychiatric/psychological assessments, urine drug test) * Willingness to taper down mood stabilizers and other relevant medications (including but not limited to: antidepressants, antipsychotics, lithium, benzodiazepines, Monoamine oxidase inhibitors (MAOIs), Selective serotonin reuptake inhibitors (SSRIs), Serotonin and norepinephrine reuptake inhibitors (SNRIs), A serotonin-norepinephrine-dopamine reuptake inhibitors (SNDRIs), Tricyclic antidepressants (TCAs), stimulants, cannabis, and other medications, supplements or therapeutics that affect serotonergic function) for the duration of the study before and during administration days (starting 5 weeks before administration), and be off medication for at least 2 weeks prior to administration * Willingness to stop allowed medication at least 24 h prior to administration of psilocybin as advised by study physician (e.g., benzodiazepines) * Ability to complete all protocol required assessment tools without any assistance or alteration to the copyrighted assessments, and to comply with all study visits Exclusion Criteria: * Participants who do not read/speak English * Active suicidal ideation with at least some intent and/or plan (i.e., a current score of 4 or 5 on the C-SSRS) * History of medically significant suicide attempt in the last 6 months * Current or past history of Bipolar I disorder, psychotic symptoms or psychotic disorder, (including but not limited to schizophrenia, delusional disorder, schizoaffective disorder) clinically relevant personality disorder (such as borderline, antisocial, narcissistic or paranoid personality disorder), or any serious psychiatric comorbidity considered negatively impacting participation or safety (e.g., PTSD or severe substance use or alcohol disorder) assessed by medical history and/or a structured clinical interview * Have a first or second degree relative with Bipolar I disorder or a psychotic disorder * Currently experiencing a hypomanic or mixed-symptom episode * Have a psychiatric or other condition judged to be incompatible with establishment of rapport or safe exposure to psilocybin * Any indication of a Personality Disorder (PD) such as but not limited to Borderline, Narcissistic, Antisocial, Paranoid, or Schizotypal PD based on Structured Clinical Interview for DSM-5 for PD and/or clinical judgment