The exact cause of bipolar disorder is unknown, but several factors seem to be involved in causing and triggering bipolar episodes:

•Biological differences. People with bipolar disorder appear to have physical changes in their brains. The significance of these changes is still uncertain but may eventually help pinpoint causes.

•Neurotransmitters. An imbalance in naturally occurring brain chemicals called neurotransmitters seems to play a significant role in bipolar disorder and other mood disorders.

•Hormones. Imbalanced hormones may be involved in causing or triggering bipolar disorder.

•Inherited traits. Bipolar disorder is more common in people who have a blood relative (such as a sibling or parent) with the condition. Researchers are trying to find genes that may be involved in causing bipolar disorder.

•Environment. Stress, abuse, significant loss or other traumatic experiences may play a role in bipolar disorder.