Diagnostic Symptoms of Major Depressive Disorder
Major depressive disorder requires the presence of 5 or more specific symptoms during the same 2-week period, with at least one symptom being either depressed mood or loss of interest/pleasure, and these symptoms must cause clinically significant distress or functional impairment. 1
Core Diagnostic Criteria
According to the American Psychiatric Association criteria referenced in multiple guidelines, the diagnosis requires:
Required Symptom Threshold
- 5 or more symptoms present during the same 2-week period
- Represents a change from previous functioning
- At least 1 symptom must be:
- Depressed mood, OR
- Loss of interest or pleasure (anhedonia)
The Nine Diagnostic Symptoms
Depressed mood most of the day, nearly every day
- In children and adolescents, this can present as irritable mood rather than sadness 1
Markedly diminished interest or pleasure in all, or nearly all, activities most of the day, nearly every day
Significant weight change or appetite disturbance
- Weight loss when not dieting or weight gain (>5% of body weight in a month)
- Increased or decreased appetite nearly every day
- In children/adolescents: failure to make expected weight gains 1
Sleep disturbance: Insomnia or hypersomnia nearly every day
Psychomotor changes: Agitation or retardation nearly every day (observable by others, not merely subjective feelings)
Fatigue or loss of energy nearly every day
Feelings of worthlessness or excessive/inappropriate guilt (which may be delusional) nearly every day
Diminished ability to think or concentrate, or indecisiveness nearly every day
Recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, suicide attempt, or a specific plan to commit suicide
Additional Diagnostic Requirements
Beyond the symptom count, the diagnosis requires meeting these exclusion and impact criteria:
Functional Impairment
- Symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning 1
Exclusion Criteria
The symptoms must NOT be:
- Due to direct physiologic effects of a substance (drug of abuse, medication) or general medical condition (e.g., hypothyroidism) 1
- Better accounted for by bereavement, UNLESS symptoms persist longer than 2 months OR are characterized by marked functional impairment, morbid preoccupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation 1
- Meeting criteria for a mixed episode (fluctuations qualifying for both manic and major depressive episodes) 1
Clinical Context and Heterogeneity
Important caveat: The polythetic nature of these criteria means that two patients can both meet diagnostic criteria for MDD while sharing only one symptom in common. Research has identified 119 different symptom combinations that fulfill DSM criteria 4, highlighting significant diagnostic heterogeneity. The most common presentation includes all nine symptoms, but this represents only a subset of patients 4.
The core symptoms of depressed mood and loss of interest or pleasure are consistently identified as the most prevalent and sensitive to treatment, though associated symptoms like fatigue, sleep disturbance, anxiety, and cognitive dysfunction are equally important for comprehensive evaluation and often persist even when mood symptoms improve 5.
Screening Tools
While not diagnostic on their own, validated screening instruments include:
- Patient Health Questionnaire-9 (PHQ-9): 9-item self-report scale assessing DSM-IV symptoms 6
- Hamilton Depression Rating Scale (HAM-D): Clinician-administered scale 6
- Beck Depression Inventory (BDI): Scores ≥20 suggest clinical depression 6
These tools help identify patients requiring full diagnostic evaluation but cannot replace clinical assessment 7.