Psilocybin shows efficacy to alleviate depression in human clinical trials for six or more months after only one or two treatments. Another hallucinogenic drug, esketamine, has recently been U.S. Food and Drug Administration (FDA)-approved as a rapid-acting antidepressant. The mechanistic basis for the antidepressant effects of psilocybin and ketamine appear to be conserved. The efficacy of these two medications has not, however, been directly compared either clinically or preclinically. Further, whether or not a profound subjective existential experience is necessary for psilocybin to have antidepressant effects is unknown. To address these questions, we tested psilocybin, lysergic acid diethylamide (LSD), and ketamine in a rat model for depression. As in humans, a single administration of psilocybin or LSD produced persistent antidepressant-like effects in our model. In contrast, ketamine produced only a transient antidepressant-like effect. Our results indicate that classic psychedelics may have therapeutic efficacy that is more persistent than that of ketamine, and also suggest that a subjective existential experience may not be necessary for therapeutic effects.
Keywords: Psilocybin; antidepressant; depression; forced swim test; ketamine; lysergic acid diethylamide; psychedelic.