In the United States, about 3.9 percent of the adult population has a lifetime prevalence of bipolar disorder, according to the National Institute of Mental Health.
Individuals with bipolar disorder, also called manic depressive disorder, have periods of unusually high mood (mania) and low mood (depression).
Symptoms of mania include an overly-happy mood or an irritable mood, restlessness, talking very fast, and participating in high-risk behaviors. Individuals who are manic may be easily distracted, sleep little, and have unrealistic beliefs about their abilities.
Symptoms of depression include a loss of interest in activities, low mood, trouble concentrating, and feeling tired. Individuals who are depressed may have thoughts of suicide or attempt suicide.
There are several types of bipolar disorder.
The first is bipolar I disorder, in which the individual has manic or mixed (manic and depressive symptoms occurring together) symptoms that occur for seven or more days, or has severe enough symptoms that require hospitalization.
Individuals with this type of bipolar disorder also have symptoms of depression.
With bipolar II disorder, patients do not have full mania. Instead, they experience hypomania, which is an elevated mood that is not as extreme as mania.
Individuals with bipolar II disorder also have symptoms of depression.
Individuals may be diagnosed with cyclothymia, in which they have symptoms of hypomania and mild depression.
If an individual is diagnosed with bipolar disorder NOS (not otherwise specified), she has symptoms of bipolar disorder, but she does not meet full criteria for bipolar I disorder or bipolar II disorder.
The National Institute of Mental Health noted that bipolar disorder NOS may be diagnosed if the duration of symptoms is not long enough or the individual has fewer symptoms than needed to meet full criteria.
To diagnose either bipolar I disorder, bipolar II disorder, cyclothymia or bipolar disorder NOS, the individual needs to present with certain symptoms.