THE CHEMISTRY OF MENTAL DISORDERS: NEUROCHEMICAL SYSTEMS, MOLECULAR MECHANISMS, AND TRANSLATIONAL IMPLICATIONS

Mental disorders are not attributable to a single chemical imbalance, but they are profoundly shaped by dynamic interactions among neurotransmitters, neuropeptides, neurosteroids, inflammatory mediators, genetic variation, neural circuitry, and environmental experience. This review provides an integrated overview of the chemistry of major psychiatric conditions, including major depressive disorder, bipolar disorder, schizophrenia spectrum disorders, anxiety disorders, post-traumatic stress disorder, substance-use disorders, and neurodevelopmental conditions. It examines monoaminergic, amino-acidergic, cholinergic, endocannabinoid, neuroendocrine, immune, epigenetic, and metabolic mechanisms, while emphasizing that molecular changes must be interpreted within developmental, circuit-level, and psychosocial contexts. Contemporary evidence supports dimensional, transdiagnostic frameworks such as the National Institute of Mental Health Research Domain Criteria (RDoC), which integrate molecular, cellular, circuit, behavioral, and environmental levels of analysis.