Study procedures
The study included a screening visit, five 4-h test sessions, and an end-of-study visit. Test days were separated by at least one week. The sessions were conducted in a calm hospital room. Only one research subject and two investigators were present during each test session. The test sessions began at 8:00 AM or 1:00 PM, with starting times that remained consistent within each participant across all five sessions. A urine sample was taken to verify abstinence from drugs of abuse, and a urine pregnancy test was performed in women prior to each session. The subjects then underwent baseline measurements. DMT or placebo was administered at 9:00 AM for the session that began at 8:00 AM or at 2:00 PM for the session that began at 1:00 PM. The outcome measures were repeatedly assessed for 150 min. The subjects were sent home approximately 15 min after the last measurement.