Causes of obsessive compulsive disorder (OCD)

Despite much research being carried out into obsessive compulsive disorder (OCD), the exact cause of the condition has not yet been identified.

However, in certain individuals OCD is thought to be triggered by a combination of genetic, neurological, behavioural and environmental factors.


Genetics is thought to play a part in some cases of OCD. Research suggests OCD may be the result of certain inherited genes (units of genetic material) that affect the development of the brain.

Although no specific genes have been linked to OCD, there is some evidence that suggests the condition runs in families. A person with OCD is four times more likely to have another family member with the condition compared with someone who does not have OCD.

Genetic and family studies have also shown OCD may be related to other conditions such as:

  • tics  rapid, repeated, involuntary contractions of a group of muscles
  • Tourette’s syndrome  a condition that causes a person to make repetitive movements or sounds

Some people with OCD may also have tics or Tourette’s syndrome.

Brain abnormalities

Brain imaging studies have shown that people with OCD have abnormalities in some parts of their brain, including increased activity and blood flow, and a lack of the brain chemical serotonin.

The areas of the brain affected deal with strong emotions and how we respond to those emotions. In the studies, brain activity returned to normal after successful treatment with cognitive behavioural therapy (CBT) or selective serotonin reuptake inhibitors (SSRIs).


Serotonin also seems to play a part in OCD. It is a chemical in the brain (neurotransmitter) that transmits information from one brain cell to another. Serotonin is responsible for regulating a number of the body’s functions, including mood, anxiety, memory and sleep.

It is not known for sure how serotonin contributes to OCD, but people with the condition appear to have decreased levels of the chemical in their brain.

Medication that increases the levels of serotonin in the brain, such as certain types of antidepressant, have proven effective in treating the symptoms of OCD.

Life events

An important life event such as a bereavement or family break-up may trigger OCD in people who already have a tendency to develop the condition (for example, due to genetic factors).

A life event can also affect the course of your condition. For example, the death of a loved one may trigger a fear that someone in your family will be harmed.

Stress, which can also be caused by life events, seems to make the symptoms of OCD worse. However, stress does not cause OCD on its own.

Parenting and family

OCD is not thought to be linked to upbringing, but certain factors such as having overprotective parents could increase your chances of developing OCD. 

Sometimes it can be unhelpful if a family member of someone with OCD intervenes. For example, a person with OCD may ask a member of their family for constant reassurance about one of their fears, such as whether they have locked the door.

If the family member continually reassures them that they have done something in order to make them feel better, it may prevent them seeking the help and treatment they need.


There have been reports of some children and young people developing OCD after having a severe infection caused by streptococcal bacteria.

One theory is that antibodies (infection-fighting proteins) produced by the body react with part of the brain, leading to OCD. The infection itself does not cause OCD, but triggers symptoms in children who are genetically predisposed to the condition.

Symptoms of OCD that occur as a result of an infection will usually start quickly (within one to two weeks).


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