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Obsessive-compulsive disorder

SNOMED: 191736004897 words•Updated 03/03/2026
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Exam Tips

  • Differentiate OCD from psychosis: OCD usually has preserved insight and ego-dystonic intrusive thoughts, whereas delusions are fixed beliefs.
  • In perinatal settings, intrusive harm thoughts with avoidance/checking are often OCD; assess risk carefully but do not assume intent to harm.
  • High-yield screening stems ask about excessive washing, checking, intrusive thoughts, slowness in daily tasks, and distress from order/mess.
  • First-line treatment in exams is CBT with ERP (with or without SSRI depending on severity/preference/access).
  • For pharmacology questions, mention that OCD often needs higher SSRI doses and longer trials than depression.
  • Always include suicide risk assessment and comorbidity screening in station structure.

Definition

Obsessive-compulsive disorder (OCD) is a chronic mental health disorder characterised by intrusive, recurrent obsessions and/or repetitive compulsions performed to reduce anxiety or prevent a feared outcome. The thoughts are experienced as unwanted and distressing, and the behaviours are excessive or not realistically connected to the feared event, causing clinically significant distress, functional impairment, or both.

Pathophysiology

OCD is understood as a disorder of maladaptive threat processing and habit circuitry, involving dysfunction in cortico-striato-thalamo-cortical (CSTC) loops (especially orbitofrontal cortex, anterior cingulate cortex, and caudate). Reduced top-down inhibitory control and abnormal error/salience signalling drive persistent doubt, guilt, and 'not-just-right' experiences; compulsions are negatively reinforced because they transiently reduce anxiety, which maintains the cycle. Serotonergic mechanisms are implicated by SSRI and clomipramine efficacy, while glutamatergic and dopaminergic pathways also contribute in treatment-resistant disease. Genetic loading is significant but incomplete, indicating gene-environment interaction. See Figure: CSTC loop model in standard psychiatry/neuroscience textbooks.

Risk Factors

  • Family history of OCD (higher risk in first-degree relatives)
  • Genetic vulnerability (higher concordance in monozygotic vs dizygotic twins)
  • Typical age pattern with peaks around late childhood and early adulthood
  • Pregnancy and postpartum period
  • Possible trigger state in susceptible children after infection (for example PANS-like presentations)
  • Comorbid neurodevelopmental/psychiatric conditions (for example tic disorders, autism spectrum disorder, ADHD, anxiety, depression)

Clinical Features

Symptoms

  • Intrusive unwanted thoughts/images/urges causing marked anxiety (for example contamination, harm, sexual/religious taboo thoughts, symmetry concerns)
  • Compulsions such as repeated washing, checking, ordering, repeating, counting, praying, or mental neutralising rituals
  • Avoidance of triggers and reassurance seeking
  • Time-consuming rituals (often >1 hour/day) with delay to routine tasks
  • Distress, shame, and reduced social/occupational/academic functioning
  • In perinatal OCD: intrusive thoughts of accidental or intentional baby harm with checking/avoidance, while insight is usually preserved

Signs

  • Visible ritualistic behaviour during interview (checking, arranging, repetitive questioning)
  • Irritant dermatitis or skin damage from excessive washing/cleaning
  • Excoriations or genital/anal irritation from repeated checking/washing
  • Anxious affect with preserved reality testing (unless severe poor-insight subtype)
  • Family accommodation of rituals, especially in children and adolescents
  • Comorbid depressive or anxiety features, and possible self-harm risk indicators

Investigations

Clinical psychiatric assessment (ICD-11/DSM-5 aligned) with direct OCD screening questions:Presence of obsessions and/or compulsions that are distressing, excessive, and functionally impairing
Risk assessment (self-harm/suicide and safeguarding):May identify elevated suicidality risk, particularly with comorbid depression or severe impairment
Severity measurement (for example Yale-Brown Obsessive Compulsive Scale, Y-BOCS):Quantifies baseline severity and response to treatment over time
Comorbidity assessment (depression, anxiety disorders, tics, ADHD, ASD, substance misuse, eating disorders, psychosis):Commonly detects at least one psychiatric comorbidity that alters management
Pre-treatment physical checks when indicated (for medication safety): weight/BP/pulse; ECG and blood tests if using clomipramine or if cardiac/electrolyte risk:Usually normal in primary OCD; abnormalities guide safer prescribing and monitoring

Management

Lifestyle Modifications

  • Psychoeducation for patient and family: explain obsession-compulsion cycle and treatment rationale
  • Structured self-help/CBT principles for mild symptoms and early presentations
  • Exposure and response prevention (ERP): graded exposure with prevention of rituals; avoid reassurance and family accommodation
  • Sleep regularisation, alcohol/substance reduction, and routine restoration to reduce vulnerability to symptom escalation
  • School/work liaison and functional rehabilitation planning

Pharmacological Treatment

Selective serotonin reuptake inhibitors (SSRIs, first-line medication)

  • Sertraline 50 mg once daily initially, increase in 50 mg steps to usual 100-200 mg daily (max 200 mg/day)
  • Fluoxetine 20 mg once daily initially, increase to 40-60 mg daily (usual max 60 mg/day)
  • Fluvoxamine 50 mg once daily initially, titrate to 100-300 mg/day (divide doses if higher dose)
  • Paroxetine 20 mg once daily initially, titrate to 40-60 mg daily (max 60 mg/day)

Use adequate dose and duration (often 12 weeks before judging full response); continue for at least 12 months after good response to reduce relapse. Warn about early activation/anxiety, GI effects, sexual dysfunction, hyponatraemia, bleeding risk (especially with NSAIDs/anticoagulants), and serotonin syndrome risk with interacting serotonergic drugs. In people under 25, monitor closely for suicidal ideation after initiation or dose change.

Tricyclic antidepressant (second-line/specialist use)

  • Clomipramine 25 mg daily initially, then increase gradually to 100-150 mg/day; some patients may require up to 250 mg/day in divided doses

Consider when SSRIs are ineffective or not tolerated, usually under specialist supervision. Contraindications/cautions include recent myocardial infarction, significant conduction disease/arrhythmia risk, mania history, epilepsy/seizure risk, severe liver disease, and angle-closure glaucoma risk. Monitor for anticholinergic effects, postural hypotension, QT prolongation, overdose toxicity, and interactions; consider baseline ECG where risk factors exist.

Augmentation in treatment-resistant OCD (specialist only)

  • Low-dose antipsychotic augmentation such as risperidone (for example 0.5-2 mg/day) or aripiprazole (for example 5-15 mg/day) after adequate SSRI trial

Reserved for specialist services after optimised CBT/ERP and SSRI trials. Monitor metabolic effects, extrapyramidal symptoms, prolactin effects (risperidone), and QT risk where relevant.

Complications

  • Chronic functional impairment in education, employment, and relationships
  • Reduced quality of life and social isolation
  • Dermatitis/skin damage from excessive washing
  • Delayed or avoided healthcare due to contamination fears
  • Family burden and accommodation of compulsions, especially in paediatric OCD
  • Self-harm and increased suicide risk, including risk independent of depressive symptoms
  • Persistent residual symptoms and relapse despite treatment

Prognosis

Without treatment, OCD is often chronic with fluctuating severity. CBT with ERP and serotonergic pharmacotherapy are evidence-based and can produce meaningful improvement, but relapse and residual symptoms are common, so long-term follow-up is often needed. Better outcomes are associated with earlier recognition, lower baseline severity, shorter duration before treatment, and strong initial treatment response; poorer outcomes are linked to severe illness, long untreated duration, and psychiatric comorbidity.

Sources & References

💊BNF Drug References(5)

✅NICE Guidelines(1)

📖Textbook References(20)

  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1065)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 973, 974)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1061, 1062)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1041, 1042)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1048)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1839)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1840, 1841)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 974)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1052, 1053)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 974)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1053)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1053)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1048)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1064, 1065)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1065)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1061)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1047, 1048)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1042)[context]
  • Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 673)[context]
  • Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 673)[context]

Sources

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