The Facts
We all experience a variety of moods such as happiness, sadness, and anger. Unpleasant moods and changes in mood are normal reactions in everyday life, and we can often identify the events that caused our mood to change. However, when we experience changes in mood or extremes of mood that appear "out of the blue" and make it hard for us to function, these changes are often the result of a mood disorder.
Mood disorders are medical conditions that affect our ability to experience normal mood states, and there are mainly two types: major depressive disorder (also known as unipolar depression), in which all abnormal mood changes involve a lowering of mood, and bipolar disorders (formerly known as manic-depressive disorder), in which at least some of the mood changes involve abnormal elevation of mood.
Bipolar disorder typically begins for people during their mid-twenties. It is unusual for bipolar disorder to begin in childhood without strong familial risk factors and it is rare for its onset to occur after the age of sixty (unless associated with another medical condition). Bipolar disorder occurs in about 2% of the adult population.
Causes
There is no single, proven cause of bipolar disorder, but research suggests that it is the result of abnormalities in the way some nerve cells in the brain function or communicate. Researchers also believe that there is a definite genetic link (family history), in which there is a higher risk for people who have a parent or full-sibling (i.e., a first-relative) with bipolar disorder.
Whatever the precise nature of the cause underlying bipolar disorder, it clearly makes people with the disorder more vulnerable to emotional and physical stresses. As a result, upsetting life experiences, alcohol, illicit drug use, lack of sleep, or other stresses can trigger episodes of illness, even though these stresses do not actually cause the disorder.
Mood disorders are not the fault of the person suffering from them. They are not the result of a "weak" or unstable personality. Mood disorders are treatable medical illnesses for which there are specific medications that help most people.