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NHS Choices Condition

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The exact cause of obsessive compulsive disorder (OCD) is unknown, but a number of theories have been suggested. These are outlined below.

Biological factors

There is evidence to suggest that OCD may be the result of certain inherited genes that affect the development of the brain.

No specific genes have been linked to OCD, but there is some limited evidence that the condition runs in families. For example, a person with OCD is four times more likely to have another family member with the condition than somebody who does not have OCD.

The basal ganglia

Brain imaging studies have shown that people with OCD have abnormalities in a part of the brain known as the basal ganglia (a group of nerves).

In evolutionary terms, the basal ganglia is very old, and is thought to be responsible for some of the most primitive and powerful emotions. For example, our fight or flight reflex, which is an animal's ability to recognise a potential threat and then decide whether to attack or run away.

One theory is that OCD develops as a result of a malfunction of the basal ganglia, which leads to a person with the condition believing that they are under threat. Their conscious mind knows that the threat is not real, but the subconscious, emotional power of the basal ganglia prevents the conscious mind from shaking off the anxiety and fear. As a result, the brain adopts compulsive behaviour as a kind of coping strategy.


The chemical serotonin also seems to play a part in OCD. Serotonin is a neurotransmitter, a chemical that the brain uses to transmit information from one brain cell to another.

Exactly how serotonin contributes to OCD is unknown, but medication that increases the levels of serotonin in the brain, such as certain anti-depressants, have proven successful in helping to treat the symptoms of OCD.

Adverse life events

There is some evidence that an adverse life event, such as a bereavement or family break-up, may trigger the onset of OCD in people who have a pre-existing biological or psychological predisposition (tendency) to OCD.

view information about Obsessive Compulsive Disorder on www.nhs.co.uk »

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