Health Canada describes four phases (Health Canada). Phase 1 tests an experimental drug in a small group for the first time, looking at safety, a safe dosage range and side effects. Phase 2 uses a larger group, usually 100 or more, to gather data on how well it works and its safety. Phase 3 uses even larger groups, usually 1,000 or more, and compares it with common treatments. Phase 4 happens after approval.
Labels like “2a” and “2b” split phase 2 into earlier and later steps. ClinicalTrials.gov uses “Phase Not Applicable” for studies without FDA-defined phases, such as behavioural interventions (ClinicalTrials.gov glossary). Psilocybin research is mostly phase 2: the 233-person treatment-resistant depression trial was phase 2 (Goodwin et al., 2022), and the 2026 EPISODE trial was phase 2b (Mertens et al., 2026).
The first psilocybin phase 3 programme is COMP360’s. Its company reported that two phase 3 trials, COMP005 and COMP006, met their primary endpoints (Form 10-Q, 5 August 2026). In psychedelic research, a later phase means more people and stricter comparison, not proof that a drug works.
Sources
- Health Canada: Clinical trials and drug safety
- ClinicalTrials.gov: Glossary terms
- Goodwin et al., NEJM, 2022
- COMPASS Pathways Form 10-Q, 5 August 2026
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