Clozapine and obsessive-compulsive symptoms: Integrating clinical outcomes, mechanisms, and precision psychiatry approaches.

Clozapine remains the gold-standard treatment for treatment-resistant schizophrenia owing to its superior antipsychotic efficacy and anti-suicidal properties, yet it is frequently associated with the emergence of obsessive-compulsive symptoms (OCS). Epidemiological studies estimate that 20-76% of clozapine-treated patients develop OCS, which often follow a chronic or fluctuating trajectory. Early recognition is critical, as untreated symptoms may persist and substantially impair psychosocial, occupational, and cognitive functioning. Younger age at clozapine initiation, prolonged illness duration, elevated clozapine plasma concentrations, comorbid anxiety or depressive symptoms, and gene-environment interaction (G × E) mechanisms involving glutamatergic pathway genes such as SLC1A1, DLGAP3, and GRIN2B have been associated with increased vulnerability. Current evidence suggests that the pathophysiology of clozapine-associated OCS is multifactorial and involves serotonergic and dopaminergic dysregulation within orbitofrontal-striatal-thalamic circuitry, superimposed upon underlying genetic and glutamatergic susceptibility. While pharmacologically mediated mechanisms are strongly implicated, pre-existing subclinical obsessive-compulsive traits may also contribute, complicating causal attribution. Phenomenologically, OCS must be differentiated from psychotic symptoms to avoid inappropriate antipsychotic escalation, which may exacerbate compulsive symptomatology. Management requires a multimodal and individualized approach integrating careful clozapine dose optimization, selective serotonin reuptake inhibitor (SSRI) augmentation, antipsychotic combination strategies such as adjunctive aripiprazole, and cognitive-behavioral therapy with exposure and response prevention (CBT-ERP). Routine therapeutic drug monitoring, structured symptom assessment, and longitudinal functional evaluation remain essential for optimizing outcomes. In conclusion, clozapine-associated OCS represent a clinically significant and mechanistically complex phenomenon arising from interactions among pharmacological exposure, neurobiological vulnerability, and individual susceptibility factors. Early detection and integrated management can mitigate functional impairment without compromising clozapine efficacy. Future research should clarify neurobiological mechanisms, validate biomarker-informed risk stratification approaches, and prioritize patient-centered functional outcomes to advance precision psychiatry in this population.