Bipolar disorder, previously known as manic depression, is a mood disorder characterized by periods of depression and periods of abnormally-elevated mood that last from days to weeks each.[4][5][7] If the elevated mood is severe or associated with psychosis, it is called mania; if it is less severe, it is called hypomania.[4] During mania, an individual behaves or feels abnormally energetic, happy or irritable,[4] and they often make impulsive decisions with little regard for the consequences.[5] There is usually also a reduced need for sleep during manic phases.[5] During periods of depression, the individual may experience crying and have a negative outlook on life and poor eye contact with others.[4] The risk of suicide is high; over a period of 20 years, 6% of those with bipolar disorder died by suicide, while 30–40% engaged in self-harm.[4] Other mental health issues, such as anxiety disorders and substance use disorders, are commonly associated with bipolar disorder.[4]

While the causes of bipolar disorder are not clearly understood, both genetic and environmental factors are thought to play a role.[4] Many genes, each with small effects, may contribute to the development of the disorder.[4][8] Genetic factors account for about 70–90% of the risk of developing bipolar disorder.[9][10] Environmental risk factors include a history of childhood abuse and long-term stress.[4] The condition is classified as bipolar I disorder if there has been at least one manic episode, with or without depressive episodes, and as bipolar II disorder if there has been at least one hypomanic episode (but no full manic episodes) and one major depressive episode.[5] If these symptoms are due to drugs or medical problems, they are not diagnosed as bipolar disorder.[5] Other conditions that have overlapping symptoms with bipolar disorder include attention deficit hyperactivity disorder, personality disorders, schizophrenia, and substance use disorder as well as many other medical conditions.[4] Medical testing is not required for a diagnosis, though blood tests or medical imaging can rule out other problems.[11]