Major depressive disorder (MDD)

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

Canonical definition at Shrinktionary. This entry adds the depression-specific angle.

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.

Primary source: NIMH: Major Depression statistics.

Frequently asked questions

What's 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 isn't 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's 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's 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's a question of bipolar disorder, when two or more medications haven't worked, or when symptoms include suicidal thoughts.

See where this fits in the Depression Hub on Shrinkopedia →

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Last reviewed March 15, 2026.

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