What Is Depression?

Everyone has periods of feeling sad, down, or blue, but clinical depression is more than a passing mood. It is characterized by pronounced feelings of sadness or irritability that last at least two weeks and are associated with impairment in daily functioning. Depressive symptoms are a central feature of depressive and bipolar disorders, which are known as mood disorders.

Depressive disorders include Major Depressive Disorder and Dysthymic Disorder. Major Depressive Disorder is characterized by periods of persistent and pervasive depressed or irritable mood, loss of interest or pleasure in usual activities, and other symptoms including changes in appetite, weight, or sleep patterns; fatigue or loss of energy; restlessness or lethargy; feelings of worthlessness or excessive or inappropriate guilt; difficulty thinking, concentrating, or making decisions; and suicidal thoughts or behavior. In some people with severe depression, psychotic symptoms (delusions or hallucinations) may be present. The symptoms of Dysthymic Disorder are similar to those of Major Depressive Disorder, but are fewer in number, lesser in severity, and longer in duration. In some circumstances, a person may have both Major Depressive Disorder and Dysthymic disorder.

Bipolar disorders include Bipolar Disorder and Cyclothymic Disorder. Bipolar Disorder (also known as manic depression) is characterized by cycling between periods of depression, mania or hypomania, and/or mixed depressive and manic symptoms. Symptoms of mania include elated mood, racing thoughts, inflated views of one's abilities or unrealistically positive expectations, excessive or pressured talking, decreased need for sleep, extreme distractibility, highly energetic or agitated behavior, and excessive involvement in high-risk pleasurable activities. There are several different forms of Bipolar Disorder, which are characterized by varying combinations of depressive, manic or hypomanic, and mixed episodes. The symptoms of Cyclothymic Disorder are similar to those of Bipolar Disorder, but are characterized by longer duration and less severe depression.

Depressive symptoms are seen in a number of other disorders as well. They are a prominent feature of certain types of Adjustment Disorders, in which  emotional or behavioral symptoms develop in response to specific stressful  events or circumstances. They may also be seen in Schizoaffective Disorder, which is characterized by the presence of co-occurring mood and psychotic symptoms. They can result directly from the use of alcohol or drugs, including prescription and nonprescription medications, and in such circumstances are categorized as Substance-Induced Mood Disorder. They can also result directly from physiological changes related to medical conditions such as heart disease, stroke, thyroid disorders (for example, hypothyroidism or Grave’s Disease), autoimmune disorders such as lupus and AIDS, and some cancers. In such cases, they are categorized as Mood Disorder Due to a General Medical Condition.

Depressive symptoms are frequently seen in people who have lost family members, friends, pets, or other loved ones, and are usually considered to be a normal response to such losses. Bereavement may look very similar to a depressive disorder, but a diagnosis of depression may be appropriate when depressive symptoms persist for an extended period of time or certain features are present (for example, excessive feelings of guilt or worthlessness, marked lethargy, pronounced difficulty in daily functioning, hallucinations, suicidal ideation or behavior).