The cause of depression in adults is not known. Depression is probably caused by a combination of biochemical, genetic and environmental factors. There are a wide variety of possible causes. This condition may be inherited, or it may be learned behavior.

Types

Major depression lasts six months or longer. Atypical depression is characterized by overeating or oversleeping. Postpartum depression occurs in some women shortly after having a baby and may be caused by hormonal changes or fatigue. Seasonal affective disorder is most likely due to lack of sunlight.

Genetics

Depression often runs in families, and genetics are thought to be a factor in causing depression. Researchers are trying to identify genes that are involved in triggering it.

Environment

External events can cause depression. Examples are death of a loved one, major illness, loss of a job and financial problems. Having a pessimistic outlook on life may be a learned behavior.

Chemical Causes

Depression can be caused by drug or alcohol abuse. Certain prescription medications can trigger depression, such as high blood pressure medication and sleeping pills. Some nutritional deficiencies may be a factor, such as a shortage of omega-3 fatty acids or folate.

When to Call the Doctor

If you are depressed for two weeks or more, call your doctor. Call 911 or get to an emergency room if you have thoughts of suicide. Don't change or stop any medication without discussing this with your doctor.

Source:

National Library of Medicine: Depression

More Information:

Mayo Clinic