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    Major depressive disorder

    Also known as MDD, clinical depression, major depression, depressive disorder

    Major depressive disorder, also called clinical depression, is a mental disorder marked by low mood or loss of interest lasting most of the day, nearly every day, for at least two weeks.[1][2] It affects an estimated 5.2% of adults worldwide and is treated mainly with psychotherapy and medication.[3][4]

    Editor reviewedStrict sourcingUpdated WikiMental health, Health and medicine
    Key facts

    If you are struggling or thinking about suicide, help is available now. In the US, call or text 988 or chat at 988lifeline.org.[5] In the UK and Ireland, call Samaritans free on 116 123.[6] Elsewhere, find a local helpline at findahelpline.com.[7]

    Major depressive disorder (MDD) is the clinical name for what most people call depression.[1] WHO counts it among the most common mental disorders and says it can lead to suicide, but that effective treatment exists for mild, moderate and severe forms.[8][9] This page is general information, not medical advice; talk to a clinician about any symptoms or treatment decisions. For a plain-language introduction, start with Depression explained.

    Definition and diagnosis

    NIMH says a diagnosis of depression requires symptoms most of the day, nearly every day, for at least two weeks, one of which must be depressed mood or loss of interest or pleasure in most activities; children and adolescents may present with irritability instead.[2] Other symptoms include hopelessness, guilt or worthlessness, fatigue, poor concentration, sleep and appetite changes, unexplained aches, and thoughts of death or suicide.[10] WHO classifies an episode as mild, moderate or severe according to the number and severity of symptoms and their effect on daily functioning.[11]

    Because some medications and medical conditions, such as viral illness or thyroid disorders, can mimic depression, a clinician may use a physical exam, interview and lab tests to rule them out.[12] Screening questionnaires support but do not replace this assessment. The PHQ-9, validated in 2001, uses scores of 5, 10, 15 and 20 as thresholds for mild to severe depression; a score of 10 or more had 88% sensitivity and specificity for major depression in the original study.[13][14]

    NIMH distinguishes major depression from persistent depressive disorder (dysthymia), in which milder symptoms last usually at least two years.[15] It also describes forms tied to particular circumstances, including perinatal depression, seasonal affective disorder and depression with psychosis.[15] The FDA describes postpartum depression as a major depressive episode that typically begins after childbirth but can start late in pregnancy.[16] Bipolar disorder includes depressive episodes alternating with manic symptoms and is treated with different medicines.[11]

    Causes and risk factors

    WHO describes depression as the result of a complex interaction of social, psychological and biological factors, with adverse life events such as unemployment, bereavement and trauma raising risk.[17] NIMH adds that genetic, biological, environmental and psychological factors all play a role.[1] WHO says prevention programmes, including school-based coping programmes and exercise programmes for older adults, have been shown to reduce depression.[18]

    Epidemiology

    WHO estimates that 5.2% of adults worldwide (4.1% of men and 6.2% of women) experienced depression in 2023, about 322 million people in total.[3] In the US, NCHS measured past-two-week depression in 13.1% of people aged 12 and older in 2021–2023, up from 8.2% a decade earlier.[19][20] The 2021 NSDUH estimated that 8.3% of adults and 20.1% of adolescents had a major depressive episode in the past year.[21][22] NIMH cautions that 2021 survey estimates are not comparable with earlier years.[23]

    Treatment reach is incomplete. In 2021, 61.0% of US adults and 40.6% of adolescents with a major depressive episode received treatment.[24] Globally, WHO says only about one third of people with depression in high-income countries get mental health treatment.[25]

    Treatment

    Treatment typically involves psychotherapy, medication or both, with brain stimulation for people who do not respond enough.[4] WHO recommends psychological treatment first, adding antidepressants for moderate and severe depression, and says antidepressants should not be used to treat depression in children.[26][27] For depression that has not improved after at least two antidepressants, FDA-approved options include esketamine nasal spray, and the most used brain stimulation therapies are ECT and rTMS.[28][29][30] The treatments guide compares these options, and the analysis of new treatments covers psilocybin and other emerging approaches.

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    Questions readers ask

    What are the diagnostic criteria for major depressive disorder?

    According to NIMH, symptoms must be present most of the day, nearly every day, for at least two weeks, and one of them must be depressed mood or loss of interest or pleasure. Children and adolescents may be irritable rather than sad.[2]

    How many people have major depression in the US?

    The 2021 national drug use and health survey estimated that 21.0 million US adults (8.3%) had a major depressive episode in the past year, with the highest rate among 18- to 25-year-olds.[21]

    What is treatment-resistant depression?

    NIMH defines it as depression that does not improve after trying at least two antidepressants.[28]

    Is major depressive disorder the same as bipolar disorder?

    No. Bipolar disorder includes depressive episodes but also manic or hypomanic episodes, and it is treated differently.[15][11]

    Sources

    · 30 claims from 8 publishers

    Each numbered claim is a statement we checked against the sources listed with it. Tap a number in the text to see its sources in place.

    1. [1]

      NIMH says depression, also called major depressive disorder or clinical depression, differs from ordinary sadness and can cause severe symptoms affecting how a person feels, thinks and handles daily activities; genetic, biological, environmental and psychological factors play a role. confirmedas of 2026-10-11

    2. [2]

      NIMH says a depression diagnosis requires symptoms most of the day, nearly every day, for at least two weeks, with one symptom being depressed mood or loss of interest or pleasure; children and adolescents may be irritable rather than sad. confirmedas of 2026-10-11

    3. [3]

      WHO estimates that in 2023 about 4% of the world's population experienced depression, including 5.2% of adults (4.1% of men and 6.2% of women), or approximately 322 million people. confirmedas of 2026-09-11

    4. [4]

      NIMH says depression treatment typically involves psychotherapy, medication or both, with brain stimulation therapy an option if these do not reduce symptoms enough; finding the best treatment may take trial and error. confirmedas of 2026-10-11

    5. [5]

      The 988 Suicide & Crisis Lifeline provides free, confidential emotional support by call, text or chat to people in suicidal crisis or emotional distress 24 hours a day across the US and its territories, through a network of over 200 local crisis centers. confirmedas of 2026-10-11

    6. [6]

      In the UK and Ireland, Samaritans can be called free on 116 123, day or night. confirmedas of 2026-10-11

    7. [7]

      Find A Helpline lists free, confidential helplines verified with crisis centers in more than 175 countries. confirmedas of 2026-10-11

    8. [8]

      WHO describes depressive disorder as a common mental disorder involving a depressed mood or loss of pleasure or interest in activities for long periods of time, different from regular mood changes. confirmedas of 2026-09-11

    9. [10]

      Common signs listed by NIMH include persistent sad, anxious or empty mood; hopelessness; irritability; guilt or worthlessness; loss of interest in activities; fatigue; trouble concentrating; sleep and appetite changes; unexplained aches; and thoughts of death or suicide. confirmedas of 2026-10-11

    10. [11]

      According to WHO, symptoms of a depressive episode last most of the day, nearly every day, for at least two weeks, and episodes are classed as mild, moderate or severe by the number and severity of symptoms and their impact on functioning. confirmedas of 2026-09-11

    11. [12]

      NIMH notes that certain medications and medical conditions, such as viruses or thyroid disorders, can cause the same symptoms as depression, and a provider can rule these out with an exam, interview and lab tests. confirmedas of 2026-10-11

    12. [13]

      The PHQ-9 is the nine-item depression module of the Patient Health Questionnaire, validated by Kroenke, Spitzer and Williams in 2001; scores of 5, 10, 15 and 20 mark the lower limits of mild, moderate, moderately severe and severe depression. confirmedas of 2001-09-01

    13. [14]

      In the 2001 validation study, a PHQ-9 score of 10 or more had 88% sensitivity and 88% specificity for major depression against a structured mental health professional interview. confirmedas of 2001-09-01

    14. [15]

      NIMH describes persistent depressive disorder (dysthymia) as less severe symptoms lasting usually at least two years, and lists other forms including seasonal affective disorder, depression with psychosis, perinatal depression, premenstrual dysphoric disorder and perimenopausal depression; bipolar disorder also involves depressive episodes. confirmedas of 2026-10-11

    15. [16]

      The FDA describes postpartum depression as a major depressive episode that typically occurs after childbirth but can begin in late pregnancy. confirmedas of 2023-08-04

    16. [17]

      WHO says depression results from a complex interaction of social, psychological and biological factors, and people who have gone through adverse life events such as unemployment, bereavement or trauma are more likely to develop it. confirmedas of 2026-09-11

    17. [18]

      WHO says prevention programmes have been shown to reduce depression, including school-based programmes that build positive coping in children and adolescents and exercise programmes for older adults. confirmedas of 2026-09-11

    18. [19]

      CDC's NCHS found that 13.1% of US adolescents and adults aged 12 and older had depression in the past two weeks during August 2021 to August 2023, measured as a PHQ-9 score of 10 or more. confirmedas of 2025-04-30

    19. [20]

      NCHS reported that depression prevalence among people aged 12 and older rose from 8.2% in 2013–2014 to 13.1% in August 2021–August 2023. confirmedas of 2025-04-30

    20. [21]

      According to NIMH's summary of the 2021 National Survey on Drug Use and Health, an estimated 21.0 million US adults (8.3%) had at least one major depressive episode in the past year, with the highest prevalence among adults aged 18–25 (18.6%). confirmedas of 2023-07-01

    21. [22]

      NIMH reports that in 2021 an estimated 5.0 million US adolescents aged 12 to 17 (20.1%) had at least one major depressive episode, with prevalence higher among adolescent females (29.2%) than males (11.5%). confirmedas of 2023-07-01

    22. [23]

      NIMH cautions that 2021 NSDUH estimates are not comparable with earlier years because of changes to data collection during the COVID-19 pandemic. confirmedas of 2023-07-01

    23. [24]

      In 2021, an estimated 61.0% of US adults and 40.6% of US adolescents with a major depressive episode received treatment in the past year, according to NIMH. confirmedas of 2023-07-01

    24. [25]

      WHO says only about one third of people with depression in high-income countries receive mental health treatment, citing lack of investment, too few trained providers and stigma as barriers. confirmedas of 2026-09-11

    25. [26]

      WHO says psychological treatments are the first treatments for depression and can be combined with antidepressants in moderate and severe depression, and that antidepressants are not needed for mild depression. confirmedas of 2026-09-11

    26. [27]

      WHO says antidepressants should not be used to treat depression in children and are not the first line of treatment in adolescents, in whom they should be used with extra caution. confirmedas of 2026-09-11

    27. [28]

      NIMH defines treatment-resistant depression as not getting better after trying at least two antidepressants; one option is adding a different type of medication, such as an antipsychotic or anticonvulsant. confirmedas of 2026-10-11

    28. [29]

      NIMH describes esketamine as an FDA-approved nasal spray for treatment-resistant depression, given in a doctor's office, clinic or hospital, that typically acts within a couple of hours. confirmedas of 2026-10-11

    29. [30]

      NIMH says the most used FDA-approved brain stimulation therapies for depression are electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS), generally used after psychotherapy and medication have been tried. confirmedas of 2026-10-11

    Revision history (1)
    1. Page created.

    Created Oct 11, 2026. Last reviewed by an editor on Oct 11, 2026. Next scheduled review: Jan 11, 2027.

    Cite this page

    "Major depressive disorder." ContentLora, updated Oct 11, 2026. https://contentlora.com/wiki/major-depressive-disorder

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