What are common symptoms of major depressive disorder?

Major Depressive Disorder (DSM-5 criteria): five or more of the following symptoms present during the same 2-week period and representing a change from previous functioning. At least one symptom must be depressed mood or anhedonia. Symptoms: (1) Depressed mood most of the day, nearly every day — sad, empty, hopeless; (2) Markedly diminished interest or pleasure in activities (anhedonia); (3) Significant weight loss or gain (>5% body weight in a month) or appetite changes; (4) Insomnia or hypersomnia nearly every day; (5) Psychomotor agitation or retardation observable by others; (6) Fatigue or loss of energy nearly every day; (7) Feelings of worthlessness or excessive/inappropriate guilt; (8) Diminished ability to think or concentrate, or indecisiveness; (9) Recurrent thoughts of death, suicidal ideation, suicide attempt or specific plan. Symptoms cause clinically significant distress or impairment, not attributable to substance or medical condition, not better explained by other disorder. Treatment: psychotherapy (CBT, IPT especially); antidepressants (SSRIs first-line, SNRIs, atypicals); ECT for severe/treatment-resistant; light therapy for seasonal pattern; exercise as adjunct; emerging treatments (ketamine, TMS). Onset of antidepressant effect: 2-6 weeks for full effect; suicide risk may transiently increase as energy returns before mood lifts — close monitoring critical. Recurrence common; treatment continuation often recommended for at least 6-12 months after remission.