Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and sometimes by decreased interest or pleasure in activities. Exact cause is unknown but probably involves heredity, changes in neurotransmitter levels, altered neuroendocrine function, and psychosocial factors. Diagnosis is based on history. Treatment usually consists of drugs, psychotherapy, or both, and sometimes electroconvulsive therapy.
The term depression is often used to refer to any of several depressive disorders. Three are classified, namely: major depressive disorder (often called major depression), dysthymia, and depressive disorder not otherwise specified. Two others are classified by etiology: depressive disorder due to a general physical condition and substance-induced depressive disorder.
The term depression is often used to describe the low or discouraged mood that results from disappointments or losses. However, a better term for such a mood is demoralization. The negative feelings of demoralization, unlike those of depression, resolve when circumstances or events improve; the low mood usually lasts days rather than weeks or months, and suicidal thoughts and prolonged loss of function are much less likely.
Women are at higher risk, but no theory explains why. Possible factors include greater exposure to or heightened response to daily stresses, higher levels of monoamine oxidase (the enzyme that degrades neurotransmitters considered important for mood), and endocrine changes that occur with menstruation and at menopause. In postpartum depression, symptoms develop within 4 weeks after delivery; endocrine changes have been implicated, but the specific cause is unknown. Also, thyroid function is more commonly dysregulated in women.
Clinical manifestations during the puerperium (6-week period after delivery) generally reflect reversal of the physiologic changes that occurred during pregnancy. These changes are mild and temporary and should not be confused with pathologic conditions.