The cause of bipolar disorder is not well understood.

Bipolar disorder seems to run in families. Your child is at greater risk of having bipolar disorder if a close family member such as a parent, grandparent, brother, or sister has the disorder.

Stressful or traumatic events may trigger episodes of mania or depression in a child with bipolar disorder. While it is normal for such events to cause mood changes, these reactions are much more extreme for children with bipolar disorder.

Sometimes symptoms of mania occur as a result of another medical condition, such as an overactive thyroid gland (hyperthyroidism) or multiple sclerosis. Symptoms can also develop as a side effect of some medications, such as corticosteroids or antidepressants. Using drugs or alcohol, consuming too much caffeine, or not getting enough sleep can also trigger a manic episode.