Major depressive disorder (MDD) is a mood disorder characterized by the presence of five or more of nine specific depressive symptoms — including at least one of depressed mood or anhedonia — for at least two weeks, causing clinically significant distress or functional impairment, and not better explained by substance use, medical conditions, or other psychiatric disorders.
If you are experiencing depression and want to talk to someone: The 988 Suicide & Crisis Lifeline (US) is free, confidential, and 24/7 by phone or text. Samaritans (UK) 116 123. Talk Suicide Canada 1-833-456-4566. Globally, findahelpline.com.
If you want to screen your symptoms before talking to a clinician, the LBL Depression Test takes about 3 minutes and runs entirely in your browser.
The DSM-5 criteria
Per DSM-5 (American Psychiatric Association, 2013), a major depressive episode (MDE) requires that five or more of the following nine symptoms have been present during the same 2-week period and represent a change from previous functioning, with at least one symptom being either depressed mood or loss of interest/pleasure:
| Criterion | Symptom | Captured by item |
|---|---|---|
| A1 | Depressed mood most of the day, nearly every day | Item 2 |
| A2 | Markedly diminished interest or pleasure in activities (anhedonia) | Item 1 |
| A3 | Significant weight or appetite change (not due to dieting) | Item 5 |
| A4 | Insomnia or hypersomnia nearly every day | Item 3 |
| A5 | Psychomotor agitation or retardation observable by others | Item 8 |
| A6 | Fatigue or loss of energy nearly every day | Item 4 |
| A7 | Feelings of worthlessness or excessive guilt | Item 6 |
| A8 | Diminished ability to think or concentrate, or indecisiveness | Item 7 |
| A9 | Recurrent thoughts of death, suicidal ideation, or suicide attempt/plan | Item 9 |
The symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning. They must not be attributable to the physiological effects of a substance or another medical condition. They must not be better explained by schizoaffective disorder, schizophrenia, or other psychotic disorders. And the person must never have had a manic or hypomanic episode (which would indicate bipolar rather than unipolar depression).
The 9-item depression screener developed by Kroenke, Spitzer & Williams (2001) maps directly onto these 9 criteria — each item captures one DSM symptom — making the screen unusually transparent and the interpretation of a high score relatively direct.
How common is MDD?
Hasin et al. 2018 (JAMA Psychiatry, n=36,309 US adults from the National Epidemiologic Survey on Alcohol and Related Conditions III, NESARC-III) reported the most rigorous recent prevalence estimates for DSM-5 MDD:
| Time frame | US adult population | Female | Male |
|---|---|---|---|
| Lifetime | 20.6% | 26.1% | 14.7% |
| 12-month | 10.4% | 13.4% | 7.2% |
Women are diagnosed at roughly twice the rate of men. Prevalence is highest in adults aged 18-29 and decreases with age. Lower socioeconomic status, unemployment, and chronic medical conditions are associated with elevated rates. International prevalence estimates vary but the general pattern of MDD being one of the most common psychiatric conditions worldwide is well-established (WHO 2023 Mental Health Atlas).
Differential diagnosis
Several conditions can produce depression-like symptoms or coexist with MDD. Distinguishing among them matters because treatment approaches differ.
MDD vs Bipolar depression
Bipolar disorder (Type I or Type II) is characterized by depressive episodes that alternate with manic (Bipolar I) or hypomanic (Bipolar II) episodes. The depressive episodes themselves can look identical to MDD, but the treatment is very different — antidepressants prescribed alone for bipolar depression can trigger mania or rapid cycling. The key signal is a history of unusually elevated mood, decreased need for sleep, racing thoughts, increased goal-directed activity, or impulsive decisions. The Mood Disorder Questionnaire (MDQ) is the most-used bipolar screening tool.
MDD vs Persistent Depressive Disorder (dysthymia)
Persistent depressive disorder (PDD; previously dysthymia) is chronic low-grade depression lasting two or more years without symptom-free periods longer than 2 months. It typically has fewer symptoms than full MDE but persists much longer. PDD and MDD can co-occur ("double depression"). The treatment evidence base is weaker for PDD than for MDD; longer-term psychotherapy and medication trials are typical.
MDD vs Adjustment Disorder with Depressed Mood
Adjustment disorder is depression-like symptoms that emerge in response to an identifiable stressor (job loss, relationship breakdown, illness diagnosis), are time-limited (resolving within 6 months of stressor cessation), and do not meet full MDE criteria. It does not require treatment in many cases — the symptoms resolve as the person adapts to the stressor — but warrants monitoring because it can progress to MDD.
MDD vs Grief and Bereavement
Grief after a major loss can produce many of the same symptoms as MDD. DSM-5 explicitly addresses this overlap and offers several distinguishing signals: in grief, sadness comes in waves triggered by reminders of the loss, with periods of relief; in MDD, low mood is more sustained and global. In grief, self-esteem typically remains intact; in MDD, worthlessness and self-criticism are prominent. Grief becomes "complicated grief" or "persistent complex bereavement disorder" when severe and impairing for more than 12 months.
MDD vs Medical conditions producing depression-like symptoms
Hypothyroidism, anemia, vitamin B12 deficiency, vitamin D deficiency, chronic fatigue syndrome, sleep apnea, and several medications (corticosteroids, beta-blockers, interferon, isotretinoin) can produce depression-like symptoms. A primary-care visit including bloodwork is reasonable when depression is the leading edge of the presentation, particularly when somatic symptoms (fatigue, sleep changes, appetite changes) are prominent.
Evidence-based treatments
Six broad treatment classes have strong RCT and meta-analytic support for MDD:
| Treatment | Evidence base | Best for |
|---|---|---|
| Cognitive Behavioral Therapy (CBT-D) | Cuijpers 2013 meta-analysis (115 studies, g≈0.71) | Cognitive-affective dominant depression; first-line for mild-moderate |
| Behavioral Activation (BA / BATD) | Ekers 2014 meta-analysis (26 studies, g≈0.74); Dimidjian 2006 RCT | Anhedonia-dominant or severe depression; comparable to CBT |
| Interpersonal Therapy (IPT) | Cuijpers 2013 meta-analysis | Depression with relational triggers (loss, role transitions, conflicts) |
| SSRI / SNRI medication | NICE 2022 guidelines; Cipriani 2018 network meta-analysis (522 trials) | First-line pharmacotherapy; particularly somatic-dominant depression |
| Combined therapy + medication | Hollon 2005 (60% sustained recovery vs 41% medication-only at 2 years) | Moderate-severe depression; multidimensional presentations |
| Mindfulness-Based Cognitive Therapy (MBCT) | Kuyken 2016 individual-patient meta-analysis (9 RCTs, n=1,258; 23% relapse reduction) | Relapse prevention, particularly after multiple prior episodes |
For severe or treatment-resistant cases, specialized options include intensive outpatient programs (IOP), electroconvulsive therapy (ECT), ketamine and esketamine (Spravato), repetitive transcranial magnetic stimulation (rTMS), and emerging options like psilocybin under research protocols. Choice of treatment is collaborative between patient and clinician, factoring severity, prior response, comorbidities, and patient preference.
Frequently asked questions
What is the difference between depression and major depressive disorder?
'Depression' is a colloquial term that can refer to a transient sad mood, a persistent low-grade dysphoria (persistent depressive disorder, formerly dysthymia), or full clinical major depressive disorder. Major depressive disorder is the specific DSM-5 diagnosis requiring at least 5 of 9 specific symptoms for at least 2 weeks, with clinically significant distress or functional impairment. Most people who say 'I'm depressed' are not necessarily describing MDD; clinical assessment by a qualified professional is the only reliable way to make the distinction.
How is MDD diagnosed?
MDD is diagnosed via clinical interview using DSM-5 (or ICD-11) criteria conducted by a qualified mental health professional — psychiatrist, psychologist, primary care physician with mental health training, or licensed therapist. The clinician evaluates whether at least 5 of the 9 specific symptoms have been present most of the day, nearly every day, for at least 2 weeks; whether at least one of the symptoms is depressed mood or anhedonia; whether symptoms cause clinically significant distress or functional impairment; and whether the symptoms are not better explained by substance use, medical conditions, bereavement, or other psychiatric disorders. Self-screen instruments like the LBL Depression Test can identify probable cases but cannot diagnose.
How common is MDD?
Per Hasin et al. 2018 (the most-cited recent epidemiology paper, JAMA Psychiatry, n=36,309 US adults), the lifetime prevalence of DSM-5 MDD in US adults is approximately 20.6%, and the 12-month prevalence is approximately 10.4%. Women are diagnosed at roughly twice the rate of men. Prevalence varies by country, age, socioeconomic status, and culture, but the general pattern of MDD being one of the most common psychiatric conditions worldwide is well-established.
What's the difference between MDD and bipolar depression?
MDD is unipolar — it has only depressive episodes. Bipolar disorder (Type I or Type II) is characterized by depressive episodes that alternate with manic (Bipolar I) or hypomanic (Bipolar II) episodes. The depressive episodes themselves can look identical, but the treatment is very different. Antidepressants prescribed alone for bipolar depression can trigger manic episodes or rapid cycling, which is why differential diagnosis matters. If you have a history of episodes of unusually elevated mood, decreased need for sleep, racing thoughts, increased goal-directed activity, or impulsive decisions, mention this to your clinician — it's the key signal for bipolar rather than unipolar depression.
What's the difference between MDD and grief?
Grief after a major loss can produce many of the same symptoms as MDD — sadness, sleep disturbance, fatigue, appetite changes — and DSM-5 explicitly addresses this overlap. Several signals distinguish grief from MDD: in grief, sadness comes in waves often triggered by reminders of the loss, with periods of relief; in MDD, the low mood is more sustained and global. In grief, self-esteem typically remains intact; in MDD, worthlessness and self-criticism are prominent. In grief, suicidal thoughts (when present) are typically about reuniting with the deceased; in MDD, they are typically about being a burden or escaping pain. Grief becomes 'complicated grief' or 'persistent complex bereavement disorder' when it remains severe and impairing for more than 12 months.
What treatments work for MDD?
Six broad evidence-based treatment classes have strong RCT and meta-analytic support: (1) Cognitive Behavioral Therapy (CBT) — Cuijpers 2013 meta-analysis of 115 studies; (2) Behavioral Activation — Ekers 2014 meta-analysis showing comparable efficacy to CBT; (3) Interpersonal Therapy (IPT) — strong evidence for depression with relational triggers; (4) SSRI/SNRI medication — first-line pharmacotherapy; (5) Combined therapy + medication — Hollon 2005 demonstrated 60% sustained recovery vs 41% medication-only at 2-year follow-up; (6) Mindfulness-Based Cognitive Therapy (MBCT) — Kuyken 2016 individual-patient meta-analysis showed 23% relapse risk reduction. Choice of treatment depends on severity, prior response, comorbid conditions, and patient preference. For severe or treatment-resistant cases, specialized options include intensive outpatient programs, ECT, ketamine/esketamine, and TMS.
Is MDD treatable?
Yes. MDD has one of the strongest evidence bases for effective treatment in psychiatry. Approximately 60-70% of patients respond to first-line treatment (therapy or medication), and combined treatment shows higher response rates and better relapse prevention. Even severe and treatment-resistant cases have effective options. Untreated MDD carries serious risks including suicide, work disability, relationship damage, and elevated mortality from cardiovascular disease and other physical conditions. Reaching out for help is one of the most evidence-supported actions a person experiencing MDD can take.
What is postpartum depression and how does it relate to MDD?
Postpartum depression (PPD) is MDD with onset during pregnancy or in the 4 weeks following delivery (per DSM-5 specifier; many clinicians use a more lenient 12-month window). It affects approximately 10-15% of postpartum women and is associated with elevated risks for mother and infant including impaired bonding, infant developmental delays, and maternal suicide. PPD warrants specific clinical attention; the Edinburgh Postnatal Depression Scale (EPDS) is the most-used screening instrument in this context. The LBL Depression Test screens for general depressive symptoms but is not specifically validated for postpartum populations.
References
- American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). DSM-5. APA Publishing.
- Hasin, D. S., Sarvet, A. L., Meyers, J. L., et al. (2018). Epidemiology of adult DSM-5 major depressive disorder and its specifiers in the United States. JAMA Psychiatry, 75(4), 336–346. doi.org/10.1001/jamapsychiatry.2017.4602
- Kroenke, K., Spitzer, R. L., & Williams, J. B. W. (2001). The PHQ-9: Validity of a brief depression severity measure. Journal of General Internal Medicine, 16(9), 606–613. doi.org/10.1046/j.1525-1497.2001.016009606.x
- Cuijpers, P., Berking, M., Andersson, G., Quigley, L., Kleiboer, A., & Dobson, K. S. (2013). A meta-analysis of cognitive-behavioural therapy for adult depression. Canadian Journal of Psychiatry, 58(7), 376–385. doi.org/10.1177/070674371305800702
- Ekers, D., Webster, L., Van Straten, A., Cuijpers, P., Richards, D., & Gilbody, S. (2014). Behavioural activation for depression: an update of meta-analysis of effectiveness and sub group analysis. PLOS ONE, 9(6), e100100. doi.org/10.1371/journal.pone.0100100
- Hollon, S. D., DeRubeis, R. J., Shelton, R. C., et al. (2005). Prevention of relapse following cognitive therapy vs medications. Archives of General Psychiatry, 62(4), 417–422. doi.org/10.1001/archpsyc.62.4.417
- Kuyken, W., Warren, F. C., Taylor, R. S., et al. (2016). Efficacy of mindfulness-based cognitive therapy in prevention of depressive relapse. JAMA Psychiatry, 73(6), 565–574. doi.org/10.1001/jamapsychiatry.2016.0076
- Cipriani, A., Furukawa, T. A., Salanti, G., et al. (2018). Comparative efficacy and acceptability of 21 antidepressant drugs for the acute treatment of adults with major depressive disorder: a systematic review and network meta-analysis. The Lancet, 391(10128), 1357–1366.