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What causes bipolar disorder?

2-minute read

The exact cause of bipolar disorder is not fully understood. However, experts believe that a number of different factors act together and make a person more likely to develop the condition. These are thought to be a complex mix of physical, environmental and social factors.

Chemical imbalance in the brain

Bipolar disorder is widely believed to be the result of chemical imbalances in the brain. The chemicals responsible for controlling the functions of the brain are called 'neurotransmitters', examples of which include norepinephrine, serotonin and dopamine.

If there is an imbalance in the levels of one or more neurotransmitters, it may cause the symptoms of bipolar disorder. For example, it is believed that abnormal serotonin levels in the brain may affect a person’s mood.


Bipolar disorder is also thought to be linked to genetics. Bipolar disorder seems to run in families, and the family members of a person with the condition have an increased risk of developing it themselves. If one parent has bipolar disorder, there is a 10% chance that their child will develop it. If both parents have bipolar disorder, there is a 40% chance their child will develop it.

However, no single gene is responsible for bipolar disorder and it does not follow that just because a family member has it that others will develop it. Instead, it is thought that a number of genetic and environmental factors act as triggers for the condition.


A stressful circumstance or situation often triggers the symptoms of bipolar disorder. Examples of stressful triggers include:

These types of life-altering events can cause episodes of depression throughout a person's life.

Bipolar disorder may also be triggered by physical illness, medications or illicit stimulant drugs, sleep disturbances and overwhelming problems in everyday life, such as money problems, work or relationships.

Bipolar disorder is also affected by the seasons, with symptoms of depression and mania more likely to occur in the spring.

Women who are predisposed to bipolar disorder may experience their first episode while they are pregnant or after they have their baby.

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Last reviewed: July 2018

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