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    Depression explained: symptoms, causes, numbers and treatment (2026)

    Depression is a common mental disorder in which low mood or loss of interest lasts most of the day, nearly every day, for at least two weeks.[1][2] WHO estimates it affected about 322 million people in 2023, and in the US 13.1% of people aged 12 and older had depression in 2021–2023.[3][4] Effective treatments exist, mainly psychological therapy and medication.[5][6]

    Editor reviewedStrict sourcingUpdated ExplainerMental health, Health and medicine

    If you are struggling or thinking about suicide, help is available now. In the US, call or text 988 or chat at 988lifeline.org.[7] In the UK and Ireland, call Samaritans free on 116 123.[8] Elsewhere, find a local helpline at findahelpline.com.[9]

    Depression is one of the most common health conditions in the world, and one of the most treatable.[1][5] This explainer is the first stop in a short course. It covers what depression is, how it is recognised, how many people it affects and the main treatment options as of October 2026. This page is general information, not medical advice. If you are worried about your mood, talk to a doctor or another qualified clinician.

    What depression is

    Everyone feels low sometimes. Depression is different: a sad, empty or irritable mood, or a loss of interest in things you used to enjoy, that lasts most of the day, nearly every day, for at least two weeks.[2] It can affect sleep, appetite, energy, concentration and self-worth, and it can make work, school and relationships harder.[10][11] It is not a personal weakness. WHO says it comes from a mix of social, psychological and biological factors, and hard life events such as job loss or bereavement raise the risk.[12]

    Clinically, depression usually means major depressive disorder (MDD), also called clinical depression.[11] A diagnosis requires symptoms most of the day, nearly every day, for at least two weeks, with depressed mood or loss of interest or pleasure as one of them; in children and adolescents irritability can replace low mood.[13] WHO grades episodes as mild, moderate or severe by symptom count, severity and functional impact, and distinguishes single-episode from recurrent depressive disorder and from bipolar disorder.[2] Related conditions include persistent depressive disorder (dysthymia), perinatal and postpartum depression, and seasonal affective disorder.[14] The entity page major-depressive-disorder covers the condition in more detail.

    Common signs

    NIMH lists common signs including a persistent sad, anxious or “empty” mood; hopelessness; irritability; guilt or worthlessness; loss of interest in hobbies; fatigue; difficulty concentrating; changes in sleep and appetite; aches without a clear physical cause; and thoughts of death or suicide.[10] Not everyone has all of them. Men may be less likely to recognise, talk about or seek help for their feelings, so their depression may go undiagnosed.[15]

    How it is diagnosed

    Only a health professional can diagnose depression. A doctor will ask about your symptoms and how long they have lasted, and may run tests, because some medicines and conditions, such as thyroid problems, can cause similar symptoms.[16] Short questionnaires like the PHQ-9 are often used to screen for depression and track it over time, but a score is not a diagnosis.[17]

    The PHQ-9 is the nine-item depression module of the Patient Health Questionnaire. In the 2001 validation by Kroenke, Spitzer and Williams, scores of 5, 10, 15 and 20 marked the lower limits of mild, moderate, moderately severe and severe depression.[17] A score of 10 or more had 88% sensitivity and 88% specificity for major depression against a structured interview.[18] CDC’s national survey uses the same 10-point cut-off to estimate prevalence.[4] Clinicians still need to rule out medical and medication causes.[16] We do not offer a self-test.

    How many people have it

    Globally, WHO estimates that about 4% of people experienced depression in 2023, including 5.2% of adults.[3] It is about 1.5 times more common in women than men, and more than 10% of women who are pregnant or have just given birth experience it.[19]

    In the US, CDC’s examination survey found that 13.1% of people aged 12 and older had depression in August 2021–August 2023, up from 8.2% in 2013–2014.[4][20] Prevalence was higher among females (16.0%) than males (10.1%), and fell as family income rose.[21][22] A separate federal survey estimated that 20.1% of US adolescents had a major depressive episode in 2021.[23] Different surveys use different methods, so their numbers are not directly comparable.[24]

    Many people go without care. WHO says only about a third of people with depression in high-income countries receive treatment.[25]

    How it is treated

    The main treatments are talking therapies and medicines, often together.[6] WHO says talking therapies come first, and medicines are added for moderate or severe depression, not needed for mild depression.[26] Antidepressants usually take 4 to 8 weeks to work.[27] Don’t start or stop a medicine without talking to your clinician.[28]

    WHO lists behavioural activation, cognitive behavioural therapy, interpersonal psychotherapy and problem-solving therapy as effective psychological treatments.[29] NIMH says moderate or severe depression is usually treated with medication from the start.[30] For treatment-resistant depression, defined as no improvement after at least two antidepressants, options include add-on medicines, esketamine nasal spray and brain stimulation such as ECT and rTMS.[31][32][33] See the depression treatments guide for detail.

    Next in this course

    Read the major-depressive-disorder reference page, then the depression treatments guide and the analysis of new depression treatments. The second half of the course covers suicide prevention, the 988 Lifeline, the crisis-line funding debate and the 988 and crisis-care tracker.

    Mental health

    Major depressive disorder

    Major depressive disorder (clinical depression): diagnostic criteria, prevalence, risk factors, screening and evidence-based treatments, as of 2026.

    Questions readers ask

    What is the difference between sadness and depression?

    Everyday sadness usually passes. In depression, a low mood or loss of interest lasts most of the day, nearly every day, for at least two weeks, and other symptoms such as sleep, appetite or concentration problems are also present.[1][2][13]

    How common is depression?

    WHO estimates about 4% of the world's population, around 322 million people, experienced depression in 2023. A CDC survey found 13.1% of Americans aged 12 and older had depression in the past two weeks in 2021–2023.[3][4]

    Can an online quiz tell me if I have depression?

    No. Questionnaires such as the PHQ-9 are screening tools used with a clinician. Diagnosis needs a health care provider, who can also rule out medical causes such as thyroid problems or medication side effects.[17][16]

    Is depression treatable?

    Yes. WHO says effective treatment exists for mild, moderate and severe depression. Psychological therapies come first, and antidepressants can be added for moderate and severe depression.[5][26]

    Is depression more common in women?

    WHO says depression is about 1.5 times more common among women than men. NIMH adds that men may be less likely to seek help, so their depression may go undiagnosed.[19][15]

    Sources

    · 33 claims from 7 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]

      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

    2. [2]

      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

    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]

      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

    5. [6]

      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

    6. [7]

      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

    7. [8]

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

    8. [9]

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

    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]

      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

    11. [12]

      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

    12. [13]

      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

    13. [14]

      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

    14. [15]

      NIMH says women are diagnosed with depression more often than men, but men may be less likely to recognise or seek help for their feelings and so are at greater risk of undiagnosed and undertreated depression. confirmedas of 2026-10-11

    15. [16]

      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

    16. [17]

      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

    17. [18]

      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

    18. [19]

      WHO says depression is about 1.5 times more common among women than men, and more than 10% of pregnant women and women who have just given birth experience depression worldwide. confirmedas of 2026-09-11

    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]

      In the same NHANES data, depression prevalence was higher in females (16.0%) than in males (10.1%). confirmedas of 2025-04-30

    21. [22]

      NCHS found depression prevalence fell as family income rose, from 22.1% among people below the poverty level to 7.4% among those at 400% or more of it. confirmedas of 2025-04-30

    22. [23]

      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

    23. [24]

      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

    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]

      NIMH says antidepressants usually take 4 to 8 weeks to work, and problems with sleep, appetite and concentration often improve before mood lifts. confirmedas of 2026-10-11

    27. [28]

      NIMH advises talking to a health care provider before starting or stopping any medication. confirmedas of 2026-10-11

    28. [29]

      WHO lists behavioural activation, cognitive behavioural therapy, interpersonal psychotherapy and problem-solving therapy as effective psychological treatments for depression, which can be delivered in person, online, or through self-help manuals and apps. confirmedas of 2026-09-11

    29. [30]

      According to NIMH, psychotherapy is often tried first for milder depression, while people with moderate or severe depression are usually prescribed medication as part of the initial treatment plan. confirmedas of 2026-10-11

    30. [31]

      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

    31. [32]

      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

    32. [33]

      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

    "Depression explained: symptoms, causes, numbers and treatment (2026)." ContentLora, updated Oct 11, 2026. https://contentlora.com/explain/depression-explained

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