Like other illnesses, depression can take different forms, such as major depression, bipolar disorder, substance abuse disorders, and Seasonal Affective Disorder.
The most common form of depression is “major depression,” which may also be called “clinical depression” or “unipolar depression.”
Individuals with major depression have a combination of persistent symptoms (see the list below) that can make it difficult for them to work, sleep, eat, and enjoy favorite activities. Periods of major depression may last for months or for several years. Major depression may occur once, twice, or multiple times during a person’s lifetime.
Symptoms of major depression may include:
- Depressed mood—feeling sad, down, or blue
- Loss of interest and enjoyment in usual activities
- Having trouble sleeping or sleeping more than normal
- Fatigue or low energy
- Poor concentration and difficulty making everyday decisions
- Loss of appetite or overeating
- Recurring feelings of guilt or worthlessness
- Physical and mental restlessness or being slowed down
- Loss of hope and thoughts of death or suicide
Depression is often accompanied by other symptoms such as nervousness or anxiety; irritability or being short-tempered; physical pain, such as headaches, muscle aches or abdominal pain; or increased sensitivity to rejection or criticism. Problem drinking is common in depression as well.
Diagnosis is usually made after a careful psychiatric evaluation by a psychiatrist, other mental health professional, or a primary care provider. The diagnosis of major depressive disorder requires five or more of the core symptoms listed above, including sad mood and/or loss of interest, during the same two-week period. Depending on the level of an individual’s distress, impairment, and medical history, treatment for depression may sometimes be initiated even in the absence of the full five symptoms.
Treatment is effective, usually within weeks, for most people with major depression. Without treatment, symptoms can persist for weeks, months, or years. Continued treatment may help to prevent recurrence of symptoms.
Bipolar disorder (also called manic depression) is a chronic, recurring condition that includes cycles of depression and hypomania or mania. Learn more about bipolar disorder.
Substance use disorders
Substance use disorders can worsen depression and complicate treatment. Individuals with depression may also have problem substance use, most commonly involving alcohol or marijuana, but also other drugs such as heroin, cocaine, or methamphetamine. For some individuals, substance use may represent an attempt to self-medicate. When problem substance use is present, effective treatment for depression also involves actively addressing substance use.
Seasonal Affective Disorder
Seasonal Affective Disorder, or SAD, is a form of depression that is related to a certain season of the year—especially winter. SAD is often not described as a separate mood disorder but as a "specifier," referring to the seasonal pattern of major depressive episodes that can occur within major depression.
Individuals usually develop SAD during adulthood (average onset occurring in the early 20s). Approximately 10-20% of the population experience mild winter SAD, and nearly 5% develop a more pronounced form of the disorder.
Two seasonal patterns of symptoms have been identified with SAD:
- Fall-onset, also called "winter depression," in which major depressive episodes begin in the late fall to early winter months and stop during summer months
- Spring-onset, also called "summer depression," in which the severe depressive episode begins in late spring to early summer
Treatments for "winter depression" and "summer depression" often differ, and may include light therapy in addition to traditional treatments for depression.