Lucan · Conditions

Obsessive-compulsive disorder

Australian guidance: eTG Psychotropic — OCD + RANZCP

1. Definition and epidemiology

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition characterised by persistent, intrusive, unwanted thoughts or urges (obsessions) that generate significant anxiety, and by repetitive behaviours or mental acts (compulsions) performed to neutralise that distress, which are time-consuming and cause clinically meaningful functional impairment. The twelve-month prevalence in Australia is approximately 1.9% and the lifetime prevalence is 2 to 3%, with equal representation across sexes in adults; males tend to present at an earlier age, often in childhood or early adolescence, while females more commonly present in early adulthood. OCD is listed by the World Health Organization as among the ten most disabling conditions globally in terms of lost quality-adjusted life years, and the mean delay from symptom onset to adequate treatment in Australia exceeds nine years.

2. Pathophysiology

The dominant neurobiological model of OCD implicates dysregulation within the cortico-striato-thalamo-cortical (CSTC) circuits, particularly the orbitofrontal cortex, anterior cingulate cortex, caudate nucleus, and thalamus. In healthy individuals, a balance exists between direct striatal pathways (facilitating goal-directed action) and indirect pathways (suppressing unwanted actions). In OCD, hyperactivity of the direct pathway produces a failure to gate out intrusive thought representations, generating repetitive loops between the orbitofrontal cortex and caudate that are subjectively experienced as obsessions. The thalamus then fails to dampen these signals, amplifying the subjective urgency of compulsive behaviour. Serotonin modulates orbitofrontal tone, explaining the robust efficacy of serotonin reuptake inhibitors; dopamine dysregulation within the striatum is implicated in the reward-like relief produced by compulsions, reinforcing the cycle. Functional neuroimaging consistently demonstrates elevated glucose metabolism in the orbitofrontal cortex and caudate that normalises with both pharmacological and psychological treatment. Twin and family studies demonstrate heritability of approximately 40 to 65%, with higher heritability in childhood-onset cases. The glutamate system is increasingly implicated in treatment-resistant presentations.

3. Clinical presentation and diagnostic criteria

Obsessions in OCD most commonly concern contamination, harm to self or others, symmetry and order, unwanted taboo thoughts of a sexual or aggressive nature, and religious scrupulosity. Compulsions include washing and cleaning rituals, checking, counting, ordering, seeking reassurance, and mental rituals such as praying or counting silently. Crucially, the individual recognises the obsessions as products of their own mind (distinguishing OCD from psychosis), and the compulsions are performed to reduce distress rather than for pleasure. DSM-5 diagnostic criteria require the presence of obsessions, compulsions, or both; the symptoms must be time-consuming (more than one hour per day) or cause clinically significant distress or functional impairment; and the symptoms must not be attributable to a substance, medication, or another medical condition. OCD is specified as having good, fair, poor, or absent insight into the irrationality of the beliefs. The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) is the standard severity instrument. Comorbid major depressive disorder occurs in 30 to 50% of patients, social anxiety disorder in approximately 25%, and tic disorders in 15 to 30%.

4. Investigations and AU-specific cutoffs

OCD is a clinical diagnosis. Investigations serve to exclude organic contributors, establish a baseline prior to pharmacotherapy, and support monitoring of treatment-related adverse effects.

Baseline workup: - Full blood count, urea and electrolytes, liver function tests, and thyroid function tests (thyroid-stimulating hormone) prior to commencing a selective serotonin reuptake inhibitor (SSRI) or clomipramine - Fasting glucose and fasting lipid profile if commencing second-generation antipsychotic augmentation - Electrocardiogram prior to commencing clomipramine given risk of QTc prolongation; repeat electrocardiogram if dose exceeds 150 mg daily - Screen for streptococcal infection in children presenting with acute-onset OCD or OCD with tic comorbidity (consider PANDAS or PANS where abrupt onset follows streptococcal illness; anti-streptolysin O titre and throat culture are appropriate)

No AU-specific diagnostic blood cutoff exists for OCD. The Y-BOCS total score guides severity classification: 0 to 7 subclinical, 8 to 15 mild, 16 to 23 moderate, 24 to 31 severe, 32 to 40 extreme.

5. Management

The eTG Psychotropic and RANZCP Clinical Practice Guidelines recommend a stepped-care model integrating psychological and pharmacological treatment. Treatment intensity is matched to symptom severity as measured on the Y-BOCS.

Psychological therapy: Exposure and response prevention (ERP), a form of cognitive behaviour therapy (CBT), is the first-line psychological treatment for OCD across all severities. ERP involves systematic, graduated exposure to feared stimuli while the individual refrains from performing compulsions, allowing habituation of the anxiety response and extinction of the compulsive reinforcement cycle. A minimum of sixteen to twenty sessions is recommended for an adequate trial; intensity can be increased with therapist-assisted intensive formats for severe presentations. Cognitive therapy targeting overestimated threat, inflated responsibility, and intolerance of uncertainty is a useful adjunct, particularly for insight-poor presentations. In Australia, ERP-trained therapists can be accessed via mental health treatment plans (Mental Health Care Plans) with Medicare rebates for up to ten sessions per calendar year; complex cases may access an extended ten additional sessions with a referral review.

Pharmacotherapy: SSRIs are first-line pharmacotherapy. Higher doses than those used for depression are typically required and a therapeutic trial requires 8 to 12 weeks at the maximum tolerated dose before non-response is concluded. Antidepressants are continued for a minimum of twelve months after remission; longer maintenance (two or more years) is recommended for severe or relapsing presentations. When pharmacotherapy is combined with ERP, outcomes are superior to either treatment alone.

If two adequate SSRI trials fail, augmentation with low-dose risperidone or aripiprazole is the most evidence-supported strategy. For treatment-resistant cases, a tertiary psychiatry referral is warranted; options include clomipramine, glutamate-modulating agents (riluzole, N-acetylcysteine), and, for severe refractory OCD, deep brain stimulation or ablative neurosurgery at a designated centre.

6. Pharmacology and AU PBS notes

Sertraline (Zoloft, Sertralife): - First-line SSRI for OCD; target dose 100 to 200 mg daily (higher than the antidepressant dose range) - PBS listed under the authority code for OCD when prescribed by a medical practitioner; streamlined authority applicable for initial prescription - Dose titrate slowly to reduce gastrointestinal adverse effects; steady-state takes approximately one week

Fluoxetine (Prozac, Lovan, generic): - First-line SSRI; long half-life minimises discontinuation syndrome; useful when adherence is variable - Target dose 40 to 60 mg daily for OCD - PBS streamlined authority for OCD

Fluvoxamine (Luvox): - First-line SSRI with the strongest evidence base specific to OCD - Target dose 150 to 300 mg daily; divided dosing often required - PBS authority listing for OCD; significant cytochrome P450 1A2 and 2C19 inhibitor, requiring care with concomitant medications

Escitalopram (Lexapro, Esipram): - Commonly used first-line SSRI; well tolerated and once-daily dosing - Target dose 20 mg daily for OCD (double the standard antidepressant dose); QTc dose-dependently prolonged at high doses

Clomipramine (Anafranil): - Tricyclic antidepressant with serotonin reuptake inhibition; the most potent antiobsessional agent but limited by anticholinergic effects, cardiac toxicity, and narrow therapeutic index - Reserved for SSRI-refractory OCD or where SSRIs are contraindicated - Target dose 100 to 250 mg daily; electrocardiogram monitoring mandatory - PBS authority for OCD

Augmentation agents: - Risperidone 0.5 to 2 mg daily: PBS authority under antipsychotic augmentation of refractory OCD; monitor metabolic parameters - Aripiprazole 2.5 to 15 mg daily: preferred for metabolic neutrality; PBS authority as an adjunct in OCD refractory to SSRI monotherapy

7. Complications and monitoring

Chronicity and disability: Untreated OCD is a chronic condition. Approximately 40% of patients follow an episodic course, 20 to 30% a deteriorating course, and the remainder a plateau course with persistent symptoms. Long-term impairment of occupational function, social relationships, and quality of life is common even in treated patients with residual symptoms.

Depression and suicide: Comorbid major depressive disorder develops in up to 50% of patients over the illness course. Suicide risk is elevated relative to the general population, with lifetime suicidal ideation reported in up to 50% of patients and attempts in 10 to 15%. Suicidal ideation must be assessed at every review, particularly when comorbid depression is present or insight is poor.

Accommodation and family burden: Family members often accommodate compulsions to reduce the patient's distress, which inadvertently perpetuates OCD. Assessment of and guidance for family accommodation is a standard component of treatment, and family-inclusive ERP models are evidence-supported.

Pharmacotherapy monitoring: - SSRI: weight, blood pressure, and symptom severity at 2 weeks, 4 weeks, 8 weeks, and 12 weeks during initial titration; Y-BOCS at 12 weeks to formally assess response; annual review of thyroid function tests - Clomipramine: electrocardiogram at baseline and when dose exceeds 150 mg daily; liver function tests and full blood count at baseline and 6-monthly; serum clomipramine level if toxicity suspected (target trough below 300 nanogram per millilitre) - Antipsychotic augmentation: weight, body mass index, waist circumference, fasting glucose, and fasting lipid profile at 3 months then annually; blood pressure at each visit

Treatment response is defined as a 35% or greater reduction in Y-BOCS total score from baseline; remission is defined as a total Y-BOCS score below 8. Formal Y-BOCS rescoring at 12 weeks, 6 months, and annually thereafter is recommended to guide treatment decisions.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.