The cause is not clearly understood, but both genetic and environmental factors play a role. Typically many genes are involved. Environmental factors include long term stress and a history of childhood abuse.[1] It is divided into bipolar I disorder if there is at least one manic episode and bipolar II disorder if there are at least one hypomanic episode and one major depressive episode. In those with less severe symptoms of a prolonged duration the condition cyclothymic disorder may be present. If due to drugs or medical problems it is classified separately.[2] Other conditions that may present in a similar manner include: drug misuse, personality disorders, attention deficit hyperactivity disorder, and schizophrenia as well as a number of medical conditions.