Study Design
The study used a double-blind, placebo-controlled, crossover design with 2 experimental test sessions to investigate the response to LSD (100 µg p.o.) with the consecutive administration of either ketanserin (40 mg p.o.) or placebo 1 hour after LSD administration. The treatment order was random and counterbalanced. Test days were separated by at least 10 days (mean: 23 days), since several previous studies used similar between-session intervals and documented no carry-over or order effects (