Scientists are studying the possible causes of bipolar disorder. Most agree that there is no single cause. Instead, it is likely that many factors contribute to the illness or increase risk.

Brain Structure and Functioning: Some studies show how the brains of people with bipolar disorder may differ from the brains of healthy people or people with other mental disorders. Learning more about these differences, along with new information from genetic studies, helps scientists better understand bipolar disorder and predict which types of treatment will work most effectively.

Genetics: Some research suggests that people with certain genes are more likely to develop bipolar disorder than others. But genes are not the only risk factor for bipolar disorder. Studies of identical twins have shown that even if one twin develops bipolar disorder, the other twin does not always develop the disorder, despite the fact that identical twins share all of the same genes.

Family History: Bipolar disorder tends to run in families. Children with a parent or sibling who has bipolar disorder are much more likely to develop the illness, compared with children who do not have a family history of the disorder. However, it is important to note that most people with a family history of bipolar disorder will not develop the illness.