Bipolar disorder, previously known as manic depression, is estimated to affect more than 1 in 45 adults and is characterised by episodes of pathological mood states. The two poles are mania (with a predominant elated or irritable mood) and depression (with feelings of sadness, anxiety, guilt or hopelessness), but mixed states, with both mania and depression, frequently occur. Psychotic symptoms such as delusions and hallucinations are also frequent. The condition is associated with significant societal and personal burden, and can damage mental and physical health, relationships, careers and quality of life.