Obsessive-compulsive disorder (OCD) is characterised by the presence of either obsessions or compulsions, but commonly both. The symptoms can cause significant functional impairment and/ or distress.

An obsession is defined as an unwanted intrusive thought, image or urge that repeatedly enters the person's mind. Compulsions are repetitive behaviours or mental acts that the person feels driven to perform. A compulsion can either be overt and observable by others, such as checking that a door is locked, or a covert mental act that cannot be observed, such as repeating a certain phrase in one's mind.

It is thought that 1 to 2% of the population have OCD, although some studies have estimated 2 to 3%.


  • Incidence: 100.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: 1:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


The aetiology is multifactorial but possible factors include:
  • genetic
  • psychological trauma
  • pediatric autoimmune neuropsychiatric disorder associated with streptococcal infections (PANDAS)

  • depression (30%)
  • schizophrenia (3%)
  • Sydenham's chorea
  • Tourette's syndrome
  • anorexia nervosa

Clinical features



  • If functional impairment is mild
    • low-intensity psychological treatments: cognitive behavioural therapy (CBT) including exposure and response prevention (ERP)
    • If this is insufficient or can’t engage in psychological therapy, then offer choice of either a course of an SSRI or more intensive CBT (including ERP)
  • If moderate functional impairment
    • offer a choice of either a course of an SSRI (any SSRI for OCD but fluoxetine specifically for body dysmorphic disorder) or more intensive CBT (including ERP)
  • If severe functional impairment
    • offer combined treatment with an SSRI and CBT (including ERP)

Notes on treatments
  • ERP is a psychological method which involves exposing a patient to an anxiety provoking situation (e.g. for someone with OCD, having dirty hands) and then stopping them engaging in their usual safety behaviour (e.g. washing their hands). This helps them confront their anxiety and the habituation leads to the eventual extinction of the response
  • if treatment with SSRI is effective then continue for at least 12 months to prevent relapse and allow time for improvement
  • If SSRI ineffective or not tolerated try either another SSRI