Definition and Diagnosis
Major Depressive Disorder (MDD) is defined by one or more episodes of depressed mood or loss of interest/pleasure lasting at least two weeks, accompanied by additional symptoms affecting sleep, appetite, energy, concentration, and self-worth, causing significant distress or functional impairment.
Epidemiology
MDD is one of the leading causes of disability worldwide, with lifetime prevalence estimated at around 15-20% in adults. Prevalence is roughly twice as high in women as in men.
Risk Factors
Risk factors include genetic predisposition, prior depressive episodes, chronic stress or trauma, chronic medical illness, and lack of social support. Certain personality traits and substance use also increase vulnerability.
Symptoms and Subtypes
Symptoms include persistent sadness or emptiness, anhedonia, changes in sleep and appetite, fatigue, feelings of worthlessness or guilt, difficulty concentrating, and in some cases recurrent thoughts of death or suicide. Symptom presentation can vary, with some individuals showing more prominent physical complaints.
Diagnosis
Diagnosis relies on structured clinical interview against DSM-5-TR criteria, requiring at least five of nine core symptoms over a two-week period, with at least one being depressed mood or anhedonia. Screening tools such as the PHQ-9 are often used to support assessment and track severity over time.
Treatment
Evidence-based treatments include psychotherapy (such as CBT or interpersonal therapy), antidepressant medication, or a combination of both, with treatment intensity guided by severity. For treatment-resistant cases, options may include augmentation strategies or neuromodulation therapies.
Prognosis
Many people respond well to first-line treatment, though MDD carries a substantial risk of recurrence, and some individuals experience a chronic or relapsing course. Ongoing maintenance treatment and relapse-prevention strategies improve long-term outcomes.
Reference
American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders (5th ed., text rev.).