Introduction

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 1–2% of the population have OCD, although some studies have estimated 2–3%.