What is the difference between mild, moderate, and severe depression?

Differentiating Mild, Moderate, and Severe Depression

Depression severity is classified based on three key dimensions: the number of DSM-5 symptoms present (5-9 total), the intensity of those symptoms, and the degree of functional impairment experienced by the patient. 1

Severity Classification Framework

Mild Depression

• 5-6 symptoms of major depressive disorder that are mild in intensity 1
• Minimal functional impairment - patient can generally maintain daily activities with some difficulty 1
• PHQ-9 scores of 5-9 indicate mild depression 2, 3
• Hamilton Depression Rating Scale (HAM-D) scores of 8-16 suggest mild depression 1, 4

Moderate Depression

• Falls between mild and severe categories in terms of symptom count, intensity, and impairment 1
• PHQ-9 scores of 10-14 indicate moderate depression 2, 3
• Hamilton Depression Rating Scale scores of 17-23 suggest moderate depression 1, 4
• Functional impairment ranges from mild to moderate 1

Severe Depression

• All or most of the 9 DSM-5 depressive symptoms are present 1
• Severe functional impairment - patient experiences marked interference with daily functioning 1
• PHQ-9 scores of 15-19 indicate moderately severe depression, while scores of 20-27 indicate severe depression 2, 3
• Hamilton Depression Rating Scale scores ≥24 suggest severe depression 1, 4

Critical Clinical Considerations

Certain high-risk features automatically classify depression as severe, regardless of symptom count: 1

• Specific suicide plan, clear intent, or recent suicide attempt
• Presence of psychotic symptoms
• First-degree family history of bipolar disorder
• Severe functional impairment (e.g., unable to leave home)

Practical Assessment Approach

Initial Screening

• Use the PHQ-9 as the primary screening tool for depression severity 1
• The two-item PHQ-9 can be used for initial screening (anhedonia and depressed mood questions) 1
• If either item scores ≥2, complete the full 9-item assessment 1

Score Interpretation and Action

• PHQ-9 scores 1-7: Minimal symptoms, no further screening needed 1, 5
• PHQ-9 scores 8-14: Moderate symptomatology requiring further diagnostic assessment and consideration of low-intensity interventions 1, 5
• PHQ-9 scores ≥15: Moderate to severe or severe symptomatology requiring referral to psychology/psychiatry for diagnosis and treatment 1, 5

Common Pitfalls to Avoid

The three severity measures (symptom count, intensity, and functional impairment) are only moderately correlated and represent partly independent domains. 6 This means:

• A patient may have many symptoms but mild intensity
• A patient may have few symptoms but severe functional impairment
• Clinicians should assess all three dimensions rather than relying on symptom count alone 6

Do not omit item 9 of the PHQ-9 (thoughts of self-harm), as this artificially lowers scores and may miss critical risk information, though positive responses warrant immediate risk assessment 1, 5

Always identify and treat medical or substance-induced causes of depressive symptoms (e.g., interferon administration) before attributing symptoms to primary depression 1, 5