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. Depression causes feelings of sadness and/or a loss of interest in activities you once enjoyed. It can lead to a variety of emotional and physical problems and can decrease your ability to function at work and at home.
Depression can occur at any time, but on average, first appears during the late teens to mid-20s. Women are more likely than men to experience depression. Some studies show that one-third of women will experience a major depressive episode in their lifetime.
There is a high degree of heritability (approximately 40%) when first-degree relatives (parents/children/siblings) have depression.
Symptoms must last at least two weeks and must represent a change in your previous level of functioning for a diagnosis of depression.
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., inability to sit still, pacing, handwringing) or slowed movements or speech (these actions must be severe enough to be observable by others).
Feeling of worthless and guilty.
Difficulty thinking, concentrating or making decisions.