A tiny tab of acid on the tongue. A daylong trip through hallucinations and assorted other psychedelic experiences For the first time, researchers at the UNC School of Medicine have discovered precisely what the drug lysergic acid diethylamide (LSD) looks like in its active state when attached to a human serotonin receptor of a brain cell, and their first-ever crystal structure revealed a major clue for why the psychoactive effects of LSD last so long.