INTRODUCTION
anxiety
DRUG EFFECT
Psychedelic substances, including lysergic acid diethylamide (LSD) and psilocybin, are investigated as possible treatments to assist psychotherapy (Due to LSD’s long duration of action, LSD studies require more resources (e.g., time and personnel) than psilocybin studies (Ketanserin could also be a rescue medication in patients who do not tolerate the effects of LSD. Although acute effects of LSD are mostly perceived as positive, it may induce strong feelings of anxiety in some individuals and/or at higher doses (The present study investigated whether the acute subjective effects of LSD (100 µg) can be shortened by ketanserin (40 mg) if it is administered 1 hour after LSD administration. The primary predefined hypothesis was that ketanserin would shorten the subjective response, assessed by a visual analog scale (VAS; i.e., “any drug effect” duration), compared with placebo. Secondary predefined hypotheses included overall smaller subjective effects (parametrized as VAS E