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Diagnosis and clinical terms

Major depressive disorder

Shariq Refai, MD, MBA, board-certified psychiatrist and the reviewer of this article.

Reviewed by Shariq Refai, MD, MBA·Updated March 15, 2026·About 3 minutes

About this term

Quick definition
A clinical diagnosis defined by at least two weeks of persistent low mood or loss of interest, plus other symptoms, with meaningful effect on daily life.
Full clinical definition
Major depressive disorder is diagnosed when a person has had at least one major depressive episode and the episode is not better explained by bipolar disorder, a medical condition, a substance, or another psychiatric condition. A major depressive episode in the DSM-5-TR requires five or more of the following nine symptoms during the same two-week period, with at least one being depressed mood or loss of interest:
  1. Depressed mood most of the day, nearly every day.
  2. Loss of interest or pleasure in nearly all activities (anhedonia).
  3. Significant weight loss, weight gain, or appetite change.
  4. Insomnia or hypersomnia nearly every day.
  5. Psychomotor agitation or slowing observable by others.
  6. Fatigue or loss of energy nearly every day.
  7. Feelings of worthlessness or excessive or inappropriate guilt.
  8. Reduced ability to think, concentrate, or make decisions.
  9. Recurrent thoughts of death, suicidal ideation, or a suicide attempt.

The symptoms must cause meaningful distress or impairment in work, school, relationships, or other areas of life.

Epidemiology
Major depressive disorder affects an estimated 8.4 percent of U.S. adults in a given year, with a lifetime prevalence near 21 percent (NIMH, 2022). Rates are higher in women than men, and the median age of first onset is in the mid-20s, though depression can begin at any age.
What it can look like in real life
A person who used to enjoy work struggles to start anything for weeks. Sleep is fragmented or excessive. Food has no appeal or becomes constant. The mind cycles through old failures and current shortcomings. Friends do not hear back. Showers slip to twice a week. The person describes feeling empty, slow, or stuck, and often cannot pinpoint a single trigger.
How clinicians assess it
A first evaluation focuses on the pattern, the duration, and the impact. A careful history checks for past episodes of mania or hypomania, which would point to bipolar disorder. Medical contributors are checked, including thyroid function, anemia, sleep apnea, vitamin levels, chronic pain, and substance use. The PHQ-9 is the most common screening tool.
Treatment
First-line treatments include psychotherapy with strong evidence (cognitive behavioral therapy, behavioral activation, interpersonal therapy), antidepressants (SSRIs, SNRIs, bupropion), or a combination. Severity and patient preference guide the starting point. APA and NICE guidelines support both medication and psychotherapy as first-line for mild to moderate depression, with combination treatment often preferred for moderate to severe depression.
Course and prognosis
With treatment, most people improve substantially. About half respond well to the first medication tried. Of those who do not, most respond to a switch or an addition. Roughly half of patients who recover have one or more future episodes in their lifetime, which is why ongoing care and relapse awareness matter.
Related terms
Persistent depressive disorder. Bipolar depression. Treatment-resistant depression. Anhedonia.
Related articles
Major depressive disorder (Types). Treatment. Suicidal thoughts.

Sources

  • American Psychiatric Association. DSM-5-TR.
  • National Institute of Mental Health. Major Depression statistics. NIMH, 2022.
  • American Psychiatric Association. Practice Guideline for the Treatment of Patients with Major Depressive Disorder, 3rd edition.
  • NICE Guideline NG222. Depression in adults: treatment and management. 2022.

Frequently asked questions

What is major depressive disorder?
Major depressive disorder is a clinical diagnosis defined by at least two weeks of persistent low mood or loss of interest, plus other symptoms (sleep, appetite, energy, concentration, guilt, psychomotor changes, or thoughts of death), with meaningful effect on daily life. It is not the same as a difficult week or a hard season.
How long does a depressive episode last?
Untreated, an average major depressive episode lasts about six to nine months. With treatment, most people see meaningful improvement in eight to twelve weeks. Some episodes are shorter. Some last longer. Roughly half of patients who recover have one or more future episodes in their lifetime (APA Practice Guideline, 2010).
What is the difference between major depressive disorder and persistent depressive disorder?
Major depressive disorder is defined by discrete episodes of at least two weeks. Persistent depressive disorder, formerly called dysthymia, requires depressed mood for most of the day, more days than not, for at least two years in adults. A meaningful share of patients have both at once, which is sometimes called double depression.
What is the success rate of treatment for major depressive disorder?
About one in three people reach full remission on the first medication tried, and roughly half show a meaningful response. Most patients need a change in dose, a switch in medication, or an addition. With persistent care, most people reach remission. The STAR*D trial is the best-known source for these numbers.
Can major depressive disorder come back?
Yes. After a first episode, the lifetime risk of a recurrence is about 50 percent. After two episodes the risk rises further. This is why ongoing care, attention to sleep and movement, and a clear plan for early relapse signs matter, even after recovery.
When should I see a psychiatrist for depression?
A primary care clinician can manage many cases of depression. A psychiatrist is worth involving when the diagnosis is unclear, when there is a question of bipolar disorder, when two or more medications have not worked, or when symptoms include suicidal thoughts.

Last reviewed March 15, 2026.

Every clinical page on DepressionResource.org is written in plain language, dated, and reviewed by a board-certified psychiatrist against current clinical guidelines. See our editorial standards and medical review process.