Dually Acting Ligands Targeting Serotonin Receptors: Implications in CNS Disorders.

The serotonergic system remains a critical focus of neuropsychopharmacology due to its widespread influence on mood, cognition, and behavior. Despite the clinical success of selective serotonin reuptake inhibitors (SSRIs), their long-term efficacy is limited by receptor heterogeneity, desensitization, and compensatory adaptations. Recent advances suggest that ligands simultaneously modulating two serotonin (5-HT) receptor subtypes may offer superior therapeutic outcomes. This perspective summarizes progress in developing such dually acting compounds for CNS disorders, including Alzheimer's and Parkinson's disease, schizophrenia, and mood disorders. Clinically relevant examples include flibanserin (5-HT1A receptor agonist/5-HT2A receptor antagonist), pimavanserin (5-HT2A/5-HT2C receptors inverse agonist), and eltoprazine (5-HT1A/5-HT1B receptors partial agonist), alongside experimental 5-HT2A/5-HT6, 5-HT3/5-HT6 or TAAR1/5-HT2C receptors ligands. Integrating structure-activity insights and clinical findings, we discuss challenges of rational dual modulation. Advances in biased signaling, targeting distinctive conformational states, and optopharmacology utilizing photochromic ligands may further enable the design of innovative dually acting agents with improved efficacy and safety profiles.