What is bipolar mood disorder?

What causes bipolar mood disorder?

Page last updated: May 2007

Men and women have an equal chance of developing this mental illness. It most commonly appears when people are in their twenties but may occur earlier or later in life.

It is believed that bipolar mood disorder is caused by a combination of factors including genetics, biochemistry, and environmental factors.

Genetic factors

Studies of close relations, such as identical twins and adopted children whose natural parents have bipolar mood disorder, strongly suggest that the illness is genetically transmitted. Children of parents with the disorder have a greater risk of developing it.

Biochemical factors

Mania, like depression, is thought to be due, in part, to a chemical imbalance in the brain. This can be treated with medication.


Stress may play a part in triggering symptoms, but not always. Sometimes the illness itself may cause the stressful events (such as divorce or a failed business), which may then be blamed for the illness.