The present randomised crossover study (n=16) in healthy volunteers used escalating single oral doses of LSD (25–200 µg) with a placebo arm and a ketanserin (40 mg) pre-treatment to probe the role of the 5-HT2A receptor in LSD-induced altered states.
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.
Within-subject crossover including placebo and a ketanserin pre-treatment condition; six single-dose sessions per participant.
Single dose 25 µg (0.025 mg).
Single dose 50 µg (0.05 mg).
Single dose 100 µg (0.1 mg).
Single dose 200 µg (0.2 mg).
200 µg LSD plus ketanserin 40 mg oral pre-dose.
Mannitol capsule placebo, visually identical.