Depression (major depressive disorder) is a common and serious medical illness that negatively affects how you feel, the way you think and how you act. Fortunately, it is also treatable. Depression causes feelings of sadness and/or a loss of interest in activities once enjoyed. It can lead to a variety of emotional and physical problems and can decrease a person’s ability to function at work and at home.
Depression symptoms can vary from mild to severe and can include:
- Feeling sad or having a depressed mood
- Loss of interest or pleasure in activities once enjoyed
- Changes in appetite — weight loss or gain unrelated to dieting
- Trouble sleeping or sleeping too much
- Loss of energy or increased fatigue
- Increase in purposeless physical activity (e.g., hand-wringing or pacing) or slowed movements and speech (actions observable by others)
- Feeling worthless or guilty
- Difficulty thinking, concentrating or making decisions
- Thoughts of death or suicide
In major depression, the most prominent symptom is a severe and persistent low mood, profound sadness, or a sense of despair. The mood can sometimes appear as irritability. Or the person suffering major depression may not be able to enjoy activities that are usually enjoyable.
Major depression is more than just a passing blue mood, a “bad day” or temporary sadness. The symptoms of major depression are defined as lasting at least two weeks but usually they go on much longer — months or even years.
A variety of symptoms usually accompany the low mood and the symptoms can vary significantly among different people. Many people with depression also have anxiety. They may worry more than average about their physical health. They may have excessive conflict in their relationships and may function poorly at work. Sexual functioning may be a problem. People with depression are at more risk for abusing alcohol or other substances.
Depression probably involves changes in the areas of the brain that control mood. Nerve cells may be functioning poorly in certain regions of the brain. Communication between nerve cells or nerve circuits can make it harder for a person to regulate mood. Hormone changes may also negatively affect mood. An individual’s life experience affects these biological processes. And genetic makeup influences how vulnerable a person is to getting this illness.
An episode of depression can be triggered by a stressful life event. But in many cases, depression does not appear to be related to a specific event. A major depressive episode may occur just once in a person’s life or may return repeatedly. People who have many episodes of major depression may also have periods of persistent but milder depressed mood.