Obsessive-compulsive disorder (OCD) is a chronic, often debilitating mental health condition characterized by recurrent, intrusive, unwanted thoughts, images, or urges (obsessions) that cause significant distress, and/or repetitive behaviors or mental acts (compulsions) performed in an attempt to neutralize the distress, prevent feared outcomes, or follow rigid rules. Lifetime prevalence is approximately 1-2% with bimodal age of onset (childhood-adolescence in 30-50%, early adulthood in remainder), no clear sex difference in adults, but male predominance in childhood-onset. Pathophysiology involves dysfunction in the cortico-striato-thalamo-cortical (CSTC) circuits (orbitofrontal cortex, anterior cingulate, caudate nucleus, thalamus), serotonergic and glutamatergic dysregulation, and genetic vulnerability (heritability 40-50%, concordance 80% in monozygotic twins).
DSM-5-TR diagnostic criteria require: presence of obsessions, compulsions, or both; obsessions defined as recurrent and persistent thoughts/urges/images experienced as intrusive and unwanted, causing marked anxiety/distress, with attempts to ignore/suppress them or neutralize with another thought/action; compulsions defined as repetitive behaviors (e.g., handwashing, ordering, checking) or mental acts (e.g., praying, counting, repeating words) performed in response to obsessions or rigid rules, aimed at preventing/reducing anxiety or feared events but not realistically connected or excessive; symptoms time-consuming (>1 hour/day) OR cause clinically significant distress/impairment; not attributable to substance/medical condition or better explained by another mental disorder. Specifiers: insight (good/fair, poor, absent/delusional), tic-related. Symptom dimensions identified by Y-BOCS Symptom Checklist: contamination/cleaning, harm/checking, symmetry/ordering, taboo thoughts (sexual, religious, aggressive), hoarding (now separate disorder).
Treatment is multimodal: first-line pharmacotherapy requires HIGH doses of SSRIs (often higher than for depression): fluoxetine 60-80 mg, sertraline 150-200 mg, fluvoxamine 200-300 mg, paroxetine 40-60 mg, escitalopram 20-40 mg, citalopram 40 mg; response delayed (10-12 weeks at therapeutic dose) and partial (typically 30-40% reduction in Y-BOCS); clomipramine (tricyclic antidepressant with serotonergic action) is highly effective but reserved for refractory cases due to side effects (anticholinergic, cardiac, seizures). Exposure and response prevention (ERP) is the gold-standard psychotherapy: systematic exposure to feared stimuli (in vivo, imaginal) while preventing compulsive responses, allowing habituation and disconfirmation of feared consequences; cognitive therapy and acceptance-commitment therapy adjuncts. Refractory OCD (failure of >=2 SSRIs and ERP) treated with: clomipramine + SSRI combination, antipsychotic augmentation (risperidone 0.5-3 mg, aripiprazole 5-15 mg, haloperidol especially for tic-related OCD), glutamate modulators (memantine, riluzole, N-acetylcysteine), and intensive ERP. Severe treatment-resistant OCD may benefit from deep brain stimulation (DBS) of the ventral capsule/ventral striatum or nucleus accumbens, transcranial magnetic stimulation (TMS), or in selected cases neurosurgical procedures (cingulotomy, anterior capsulotomy, gamma knife).