Experimental procedure
Participants were administered 100 μg LSD orally in capsules (trial A) or vials (trial (B) and identical mannitol and ethanol-filled placebo capsules/vials in a cross-over design across two separate experimental sessions with a time between sessions of at least 7 days (17 ± 35.3 days [median ± SD], range: 7−182 days). Each session included an assessment of brain activity during rest using fMRI, which was acquired 140.5 ± 10.9 min [median ± SD] (range: 121−200 min) after administration of LSD or placebo. (see Supplement for data acquisition parameters and preprocessing procedure). Participants were instructed to close their eyes and remain awake during the scan. Subjective effects were assessed with the 5 Dimensions of Altered States of Consciousness (5D-ASC) scale [