Both are etiologically-linked depression rather than an independent mood disorder or an adjustment reaction, but the causal agent differs: a medical condition's direct physiological effect versus a substance or medication's pharmacological effect.
Medical-condition-related depression tracks the course of the underlying illness; substance/medication-induced depression tracks intoxication, withdrawal, or medication exposure specifically.
Medical-condition-related depression may persist until the medical condition is treated (e.g., hypothyroidism corrected); substance/medication-induced depression is expected to resolve with clearance or discontinuation of the specific agent.
Medical-condition-related presentations often include other physical signs of the specific illness (e.g., hypothyroid signs: fatigue, cold intolerance, weight gain); substance/medication-induced presentations track the specific agent's pharmacological profile.
Both can be severe, including suicidal ideation; impairment severity alone does not distinguish which etiology is responsible, and suicide risk should be assessed with equal seriousness regardless of cause.
An adjustment disorder with depressed mood (an emotional reaction to receiving a diagnosis) should be distinguished from a direct physiological effect of the medical condition itself, and a medication used to treat the condition should be considered as a possible substance/medication-induced cause in its own right.
The key differential question is whether depression is a direct effect of the disease process itself or a direct pharmacological effect of a substance or medication involved in its treatment — both should be considered and can co-occur.
It can be genuinely difficult to separate 'depressed because of the biology of the illness' from 'depressed because of a medication used to treat it' or 'depressed as an emotional reaction to being ill' — all three should be actively considered rather than defaulted to one.
Depressive symptoms improving substantially once a hormonal abnormality is corrected point to the medical-condition form; depressive symptoms appearing after starting a specific medication for that condition point to the substance/medication-induced form.
| Feature | Depressive Disorder Due to Another Medical Condition | Substance/Medication-Induced Depressive Disorder |
|---|---|---|
| Causal mechanism | Due to Medical Condition: direct physiological effect of the disease process itself | Substance/Medication-Induced: pharmacological effect of a specific agent |
| Course relative to treatment | May resolve with treatment of the medical condition | Resolves as the specific agent clears or is discontinued |
| Typical example | Untreated hypothyroidism | Interferon therapy prescribed for an unrelated condition |
A prominent and persistent disturbance of mood characterized by depressed mood or markedly diminished interest/pleasure that is judged, from history, physical exam, or laboratory findings, to be the direct pathophysiological consequence of another medical condition (such as hypothyroidism, stroke, or Parkinson's disease).
A prominent and persistent disturbance of mood characterized by depressed mood or markedly diminished interest/pleasure that developed during or soon after substance intoxication, withdrawal, or exposure to a medication capable of producing depressive symptoms, where the substance/medication is judged etiologically related to the disturbance.