This Phase I/Phase II, randomised, double-blind, quadruple-masked trial (n=50) will evaluate a single oral dose of psilocybin 5 mg, 10 mg or 25 mg, given alongside psychotherapy, in veterans and first responders with treatment-resistant depression (TRD) and co-occurring substance use disorder (SUD). The study will assess safety and tolerability, as well as whether psilocybin-assisted psychotherapy can reduce substance use severity and depressive symptoms. Participants will be assigned in parallel to one of three psilocybin dose groups and will complete two intake visits, three preparatory psychotherapy sessions, an 8 to 10 hour dosing session, and three weekly integrative psychotherapy sessions afterwards. Outcomes include adverse events, urine drug results, days of substance use, depression symptom ratings, plasma brain-derived neurotrophic factor (BDNF) during stress exposure, and resting brain functional connectivity on MRI, with repeated daily assessments across 6 weeks and follow-up through 12 weeks, including a 60-day follow-up.
The goal of this clinical trial is to learn if a single dose of psilocybin (5mg Vs 10mg Vs 25mg) alongside psychotherapy is safe and can help treat treatment resistant depression (TRD) with co-occurring substance use disorder (SUD) in veterans and first responders. We seek to answer:
* Whether 5mgs, 10mgs and 25mgs of psilocybin are safe in individuals with co-occurring TRD and SUD
* Whether psilocybin assisted psychotherapy will reduce substance use severity and depression symptoms
* What neurobiological processes are associated with the effects of psilocybin assisted psychotherapy.
The researchers will compare the effects of a single dose of psilocybin (either 5mgs or 10mgs or 25mg) alongside psychotherapy on substance use severity and depression symptoms over six weeks in veterans and first responders with TRD and co-occurring SUD.
In this 14-week study, participants will:
* Visit the clinic for two intake sessions
* Complete seven psychotherapy sessions. This will include three sessions before psilocybin administration, an 8 to 10 hour dosing session, and three sessions following psilocybin administration
* Complete short, repeated daily assessments for six weeks, in total, before and after psilocybin administration
* Complete two brain scans before and after psilocybin administration
Experimental: Participants receive a single oral dose of psilocybin 5mgs
Experimental: Participants receive a single oral dose of psilocybin 10mgs
Experimental: Participants receive a single oral dose of psilocybin 25mgs