Major depressive disorder (MDD) is a chronic, highly prevalent, and debilitating mental disorder associated with significant illness and economic burden globally. Exposure to trauma (eg, physical, sexual, emotional abuse, and/or physical, and emotional neglect) is common among individuals with MDD. Persons with MDD and a history of trauma often exhibit an attenuated response to conventional serotonergic antidepressants compared to those with non-traumatized depression. Emerging evidence indicates that exposure to trauma is associated with increased inflammatory markers [eg, C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α)] as well as glutamatergic dysregulation in the central nervous system (CNS). It is hypothesized that individuals with MDD and a history of trauma may be conceptualized as a distinct bio-phenotype compared to non-traumatized depression. Furthermore, preliminary evidence positions select glutamatergic modulators as potential, novel, mechanistically-informed therapeutic strategies that may provide benefit to persons with elevated inflammation and glutamatergic dysregulation.

G protein-coupled receptors (GPCRs) are involved in many physiological and pathophysiological processes. Conventional pharmacological models categorize the typology of pharmacologic ligands as agonists or antagonists. Biased agonism is a relatively newer pharmacodynamic characteristic that has potential to optimize therapeutic efficacy while minimizing adverse effects in psychiatric and neurological treatments. We conducted a narrative literature review of articles obtained from PubMed, Embase, and MEDLINE from inception to April 2025, focusing on pharmacologic antagonism (i.e., competitive, noncompetitive, uncompetitive) and agonism (i.e., full, partial, inverse, superagonism, biased). Primary and secondary articles defining these concepts were included, provided they addressed pharmacologic (rather than chemical) antagonism and agonism. Distinct mechanisms of antagonism and agonism were identified, each contributing nuanced receptor modulation beyond the conventional models. Notably, biased agonism facilitates targeted intracellular signaling (e.g., G protein- versus β-arrestin–mediated). Use cases demonstrate relatively greater efficacy (e.g., incretin receptor agonist, tirzepatide) and improved safety (e.g., serotonergic psychedelics, opioids). Biased agonism provides a potential avenue for future drug development, with emerging preclinical evidence suggesting potential to differentially activate intracellular pathways and thereby improve efficacy and safety profiles of psychopharmacologic agents—pending clinical validation. Future research vistas should aim to rigorously assess the long-term outcomes of biased agonism, explicitly addressing individual variability in receptor signaling and therapeutic response.