Role of the Serotonin 5-HT2A Receptor in LSD-induced Altered States of Consciousness (LDR-Study)

This randomized, quadruple-masked, within-subject crossover study tested single oral doses of LSD (25, 50, 100, 200 µg), a 200 µg LSD plus ketanserin (40 mg) condition, and placebo in healthy volunteers to assess dose–response effects on altered states of consciousness.

Outcomes included subjective altered-state measures, safety and tolerability assessments, and physiological monitoring; ketanserin was used to pharmacologically probe the contribution of 5-HT2A receptors to high-dose LSD effects.