What is obsessive-compulsive disorder?

Obsessive-compulsive disorder (OCD) is a condition involving two main features. Obsessions are unwanted thoughts, images, or urges that come into the mind repeatedly and cause distress. Compulsions are behaviours or mental acts the person feels driven to perform, often in response to obsessions, with the goal of reducing distress or preventing some feared outcome. The classic example is fear of contamination (obsession) leading to excessive hand washing (compulsion), but OCD takes many forms.

Why it has multiple presentations. People with OCD can have very different obsession and compulsion patterns: contamination concerns, fear of harm to oneself or others, symmetry and ordering needs, religious or moral scrupulosity, sexual or relationship intrusive thoughts, hoarding tendencies, and many others. The underlying biology and the treatment approach are largely shared, but the specific symptoms can look very different.

Why it is more than just being neat or careful. The defining feature of OCD is that the obsessions and compulsions are time-consuming, distressing, and interfere with daily life. People with OCD typically recognise that their thoughts and behaviours are excessive but feel unable to stop them.

The first-line therapy options.

Cognitive-behavioural therapy with exposure and response prevention (CBT-ERP): the most-evidenced psychotherapy for OCD. The therapy involves gradual exposure to triggering situations while resisting the compulsive response, with the goal of breaking the obsession-compulsion cycle.

Selective serotonin reuptake inhibitors (SSRIs): often used at higher doses than for depression. Clomipramine, an older medicine, is also highly effective. Response usually takes 8 to 12 weeks at adequate dose.

The options for OCD that does not respond enough to first-line therapy.

Augmentation: adding low-dose atypical antipsychotics to SSRI therapy can help some patients.

Transcranial magnetic stimulation (deep TMS): a non-invasive procedure that uses magnetic pulses to stimulate brain regions involved in OCD. Approved for OCD with growing real-world use.

Deep brain stimulation (DBS): a procedure that places electrodes in specific brain regions and delivers continuous electrical stimulation. Approved for severe refractory OCD; available at specialist centres.

Novel medicines: glutamate-modulator medicines and other emerging mechanism classes are in late-stage trials.

What to expect. With appropriate therapy, most people with OCD experience meaningful improvement, and many achieve substantial recovery. CBT-ERP is highly effective when delivered by appropriately-trained therapists; access to specialist therapy is one of the most important determinants of outcome.