Everyone occasionally feels blue or sad, but these feelings are usually fleeting and pass within a couple of days. When a person has clinical depression, it interferes with daily life as well as normal functioning, and causes pain for both the person with the disorder and those who care about him or her. Depression is a common but serious illness, and most who experience it need treatment to get better.
A recent study sponsored by the World Health Organization (WHO) and the World Bank found unipolar major depression to be the leading cause of disability in the United States. Approximately 18.8 million American adults, or about 9.5 percent of the U.S. population age 18 and older in a given year, have a depressive disorder.
Many people with a depressive illness never seek medical care for it. But the vast majority, even those with the most severe depression, can get better with clinical treatment. Intensive research into the illness has resulted in the development of medications, psychotherapies, and other methods to treat people with this disabling disorder.
Source: National Institute of Mental Health (NIMH)