G protein-coupled receptors (GPCRs) are involved in many bodily processes. Traditional drug classification divides ligands into agonists or antagonists. Biased agonism is a newer concept where a drug selectively activates one intracellular signaling pathway over another, such as G protein versus β-arrestin pathways. This narrative review of literature up to April 2025 describes distinct mechanisms of antagonism and agonism beyond conventional models. Biased agonism has shown potential for greater efficacy, as with the incretin receptor agonist tirzepatide, and improved safety, as with certain serotonergic psychedelics and opioids. Preclinical evidence suggests biased agonism could improve psychiatric and neurological treatments by differentially activating pathways, pending clinical validation.
Lysergic acid diethylamide and 3,4-methylenedioxymethamphetamine activate the 5-hydroxytryptamine 2B receptor, a pathway known to cause drug-induced valvular heart disease. This systematic review of 17 studies found no research on psilocybin, dimethyltryptamine, or mescaline. Both lysergic acid diethylamide and 3,4-methylenedioxymethamphetamine show high or moderate affinity for this receptor and promote signaling linked to fibrotic changes in heart valve tissue. In vivo studies confirm serotonin-induced valvulopathy, and chronic 3,4-methylenedioxymethamphetamine use has been associated with valve abnormalities in humans. No clinical cases of lysergic acid diethylamide-induced valvulopathy have been reported, but preclinical data suggest potential for fibrotic signaling under sustained exposure. Preliminary evidence supports the need for cardiac safety monitoring in psychedelic research.