Psilocybin for alcohol use disorder: Rationale and design considerations for a randomized controlled trial

Several lines of evidence suggest that classic psychedelics (5-HT_2A receptor agonists or partial agonists) such as psilocybin might facilitate behavior change in individuals with substance use disorders. We conducted a multi-site, double-blind, randomized controlled trial (RCT) to assess the effects of psilocybin-assisted psychotherapy in alcohol-dependent volunteers. In addition to a structured 12-week psychotherapy platform, participants (n = 96) were randomly assigned (1:1) to receive either oral psilocybin or an active placebo (oral diphenhydramine) in each of two dosing sessions (at weeks 4 and 8). Initial doses were 25 mg/70 kg psilocybin or 50 mg diphenhydramine, which could be increased in the second session depending on initial response. The psychotherapy platform combined evidence-based, manualized therapy for alcohol dependence with a supportive context for the dosing sessions. All participants were followed in the RCT through week 36. At the end of the RCT, participants who still met safety criteria were offered an open-label psilocybin session. Data collected at screening, baseline and throughout the study included: demographics, measures of alcohol use, subjective response to psilocybin and diphenhydramine, and safety measures. The primary outcome was the proportion of heavy drinking days during the 32 weeks after the first dosing session (i.e., between week 4 and week 36). Secondary outcomes included safety, additional measures of drinking (e.g., abstinence, drinking days, etc.), craving, self-efficacy, and acute effects. We will also explore moderators and mediators of the primary outcome. The primary outcomes will be published elsewhere. In this paper, we describe the protocol and rationale for our design decisions.