Inhaled DMT for Major Depressive Disorder

Major depressive disorder (MDD) is a common and disabling condition associated with high functional burden, incomplete response to standard antidepressant treatments, and persistent suicide risk. Current pharmacological treatments often require weeks to months to achieve meaningful benefit and are limited by delayed onset, side effects, and non-response in a substantial proportion of patients. Other interventions, including esketamine and electroconvulsive therapy, may provide benefit in selected cases but present limitations related to durability, logistics, invasiveness, or tolerability. N,N-dimethyltryptamine (DMT) is a classic serotonergic psychedelic with rapid onset and short duration of action when administered by inhalation, with acute effects typically lasting about 10 to 20 minutes. Prior studies conducted by the study group suggested that inhaled DMT has a favorable safety and tolerability profile and may produce rapid antidepressant and antisuicidal effects. This study is a multicenter Phase 2b clinical trial designed in 2 stages. In Stage 1, participants are randomized 1:1 in a double-blind parallel-group design to receive either a higher-dose inhaled DMT regimen (15 mg followed 1 hour later by 60 mg) or a lower-dose inhaled DMT regimen used as an active comparator (1 mg followed 1 hour later by 4 mg). The total planned sample size is 140 randomized participants. Participants who do not achieve remission at Day 7, defined in the protocol as MADRS \>10, enter Stage 2, an open-label extension in which all non-remitters receive the higher-dose DMT regimen on Day 14 (±3 days). The study will also explore the clinical effects of re-dosing among non-remitters from both initial treatment groups. The trial recruits adults with DSM-5 MDD and a current moderate-to-severe depressive episode, with baseline MADRS score ≥20, stable treatment regimen for at least 4 weeks, and ability to provide informed consent. Participants are followed for up to 12 months after treatment. Recruitment is multicenter and includes psychiatric clinical sites at Brazilian universities. The primary efficacy objective is to compare the two treatment groups with respect to change in total MADRS score from baseline to Day 7. Secondary outcomes include additional depression, suicidality, safety, functioning, quality-of-life, subjective experience, and psychological measures assessed across follow-up visits through Month 12. The primary analysis follows the intention-to-treat principle. The primary endpoint is analyzed using a generalized linear mixed model / mixed model for repeated measures framework with fixed effects for treatment group, time, and treatment-by-time interaction, with participant-level random intercepts. Missing data are handled by restricted maximum likelihood estimation. Additional analyses include response and remission comparisons, effect size estimation, and exploratory associations between acute subjective effects, biomarkers, and clinical outcomes.