Psilocybin Phase III trials. Where things stand.

The two trials that matter most

COMPASS Pathways — treatment-resistant depression

COMPASS Pathways' Phase III programme uses COMP360, the company's proprietary synthetic psilocybin formulation, in adults with treatment-resistant depression (defined as failure to respond to at least two prior antidepressant treatments). The programme consists of two studies: COMP005 (a single-dose protocol) and COMP006 (a two-dose protocol with optional re-dosing).

COMPASS announced positive topline results from COMP005 in mid-2025, with the 25mg dose meeting its primary endpoint of reduced depression severity at 6 weeks compared to placebo. COMP006 readout is expected in late 2026. If both trials read out positively, COMPASS has signalled an FDA submission for late 2026 or early 2027.

Usona Institute — major depressive disorder

Usona Institute, a non-profit medical research organisation, is running a parallel Phase III programme for major depressive disorder (a broader indication than treatment-resistant depression). Usona's lead compound is also synthetic psilocybin, with Phase II results in 2023 showing strong antidepressant effects after a single 25mg dose. Phase III is ongoing.

The Usona programme is notable for its non-profit structure, intended to reduce some of the commercial pressures that complicate psychiatric drug pricing. If approved, the pricing strategy could meaningfully affect access.

What "approval" would actually mean

FDA approval of psilocybin for either indication would not legalise psilocybin in any general sense. It would create a regulated pathway by which a specific synthetic formulation, administered in a specific clinical context with FDA-approved psychotherapeutic support, could be prescribed by trained clinicians for the approved indication.

The DEA would also need to reschedule psilocybin (currently Schedule I) for the approved indication. This has happened before — most recently with cannabis-derived Epidiolex, which was rescheduled after FDA approval. The timeline for DEA action typically follows FDA approval within months.

Practical access — meaning trained clinicians, certified facilities, insurance coverage — typically lags approval by a further 12–24 months as implementation infrastructure builds out. The Oregon and Colorado state programmes for regulated psilocybin therapy have informed many practitioners about what implementation actually requires.

What if the trials don't read out positively?

Methodological challenges have shadowed psychedelic clinical trials throughout. The Lykos Therapeutics MDMA-assisted therapy submission was rejected by the FDA in 2024 on a combination of trial-design issues and concerns about therapist conduct during trials. That rejection cast a long shadow over the broader psychedelic clinical pipeline.

Specific concerns that could complicate psilocybin approval: blinding (most patients can tell whether they received psilocybin or placebo), expectancy effects, the role of psychotherapy versus the drug itself, and durability of effect beyond the 6-12 week trial windows.

If Phase III trials read out negative or marginal, the approval timeline extends substantially — likely another full Phase III programme, possibly with redesigned methodology. The state-regulated pathways (Oregon, Colorado) and international jurisdictions (Australia approved psilocybin in 2023) would remain operational, but the federal US pathway would slow significantly.

What this means for people considering Mexico now

For anyone considering psilocybin treatment in the next 12-24 months, the practical reality remains: regulated access in the United States is limited to Oregon and Colorado state programmes; clinical trial enrolment requires meeting strict eligibility criteria; and outside those pathways, retreats in Mexico and a handful of other jurisdictions remain the primary route.

If the trials read out positively and approval follows, the picture shifts in 2027-2028. For now, it doesn't.

Other psilocybin programmes worth watching

• Cybin — deuterated psilocybin analogue (CYB003) for major depressive disorder. Phase III initiation expected late 2025.
• Imperial College London — ongoing investigator-initiated trials for anorexia, OCD, and chronic pain.
• Yale University — early-stage trials for migraine and cluster headache.
• Johns Hopkins — ongoing programmes for tobacco cessation, alcohol use disorder, and obsessive-compulsive disorder.

For the full set of clinical statistics with primary-source links, see our statistics page.