Sustained antidepressant-like effects of psychedelics through 5-HT_2AR-β-arrestin signaling

Psychedelics produce long-lasting antidepressant effects, but their hallucinogenic properties limit clinical use. Using structure-guided design of 5-HT_2AR-β-arrestin-biased agonists, we identified β-arrestin signaling as a critical driver of prolonged antidepressant-like effects in mice. Here we show that the slow-dissociation kinetics of lysergic acid diethylamide (LSD) enable progressive accumulation of 5-HT_2AR engagement during repeated low-dose administration, approaching the receptor occupancy achieved by an acute high dose while avoiding its high peak concentration. This kinetic separation sustains β-arrestin signaling while limiting robust Gα_q-mediated Ca²⁺ responses. Consistent with this framework, repeated low-dose LSD and repeated low-dose psilocybin pretreatment followed by a high-dose psychedelic challenge produced sustained antidepressant-like behavioral effects in mice. In parallel, these regimens produced no detectable psychedelic-associated behavioral disruption in mice and cynomolgus macaques. Together, these findings uncover the signaling basis of sustained psychedelic efficacy and provide a rational framework for developing nonhallucinogenic psychedelic therapies for psychiatric disorders.