Major depression needs two weeks of pervasive low mood to diagnose
Major depressive disorder, or clinical depression, requires a stretch of at least fourteen days marked by persistent sadness, battered self-worth, and vanishing pleasure in usual activities. U.S. clinicians coined the cluster in the mid-1970s; DSM-III adopted it in 1980. Among conditions ranked by years lived with disability, only lower-back pain outranks it—yet no lab test confirms it.
Diagnosis rests on reported experience, family observations, and mental status exam; blood tests mainly rule out mimics. Onset often falls in the twenties. About 33.2 percent of men and 43.0 percent of women with depressive symptoms report seeking help. Course ranges from a single months-long episode to lifelong recurrence. Roughly half of people with MDD describe emotional blunting or anhedonia; hopelessness and suicidal thinking can appear. Physical complaints—fatigue, headaches, digestive trouble—are the most common presenting problems in developing countries per WHO criteria.
Causes mix genes, environment, and psychology; family and twin studies put genetic contribution near forty percent of risk variation. Genome-wide studies found 44 variants in 2018 and 102 in 2019, yet heritability looks lower than for bipolar disorder or schizophrenia. Adverse childhood experiences raise risk and worsen severity and treatment response. Other links include living alone (about forty-two percent greater risk in one review), unhappy marriages, air pollution (PM2.5 and depression; short-term PM10 and suicide), lead exposure, certain drugs, chronic illness, and early substance use. A 2025 UK study of more than 172,500 adults aged 39+ found prior depression associated with chronic illness onset about thirty percent earlier.
Aaron Beck’s cognitive triad of negative thoughts about self, world, and future remains influential. Monoamine theories grew from antidepressant chemistry, but a 2022 review found no consistent evidence for a simple serotonin-level story, and the drugs’ delayed benefit versus instant monoamine rise still puzzles researchers. Typical care combines psychotherapy and antidepressants—whose clinical efficacy remains debated—plus hospitalization when self-neglect or harm risk is high. Children may show irritability and school collapse more than classic sadness; older adults may present with forgetfulness and slowed movement beside other illnesses and medications. Secondary depression can follow HIV/AIDS, asthma, Parkinson’s basal-ganglia degeneration, or iatrogenic drugs such as interferons, beta blockers, and isotretinoin; postpartum and seasonal forms track hormonal and light cycles.
Source: Major depressive disorder
