bipolar disorder, a major mood disorder characterized by episodes of mania, depression, or mixed mood. One or the other phase may be predominant at any given time, one phase may appear alternately with the other, or elements of both phases may be present simultaneously. Characteristics of the manic phase are excessive emotional displays, such as excitement, elation, euphoria, or in some cases irritability accompanied by hyperactivity, boisterousness, impaired ability to concentrate, decreased need for sleep, and seemingly unbounded energy. In extreme mania, a sense of omnipotence and delusions of grandeur may occur. In the depressive phase, marked apathy and underactivity are accompanied by feelings of profound sadness, loneliness, guilt, and lowered self-esteem. Causes of the disorder are multiple and complex, often involving biological, psychological, interpersonal, and social and cultural factors. The disorder is a biological illness that can be precipitated or exacerbated by psychosocial stressors. See also major depressive disorder.
