Depression can be considered both a symptom and a disease, depending on the context.

Nevertheless, depression is more frequently a symptom rather than a disorder.

1. Depression as a disease (major depressive disorder – MDD)

• • Depression is diagnosed as major depressive disorder (MDD) or another depressive disorder when it is persistent and meets clinical criteria. (DSM-5, American Psychiatric Association).
  • MDD is a mental illness with distinct biological, psychological, and social causes, including genetics, brain chemistry imbalances, trauma, and chronic stress.
  • It requires medical intervention, such as therapy, medication, or lifestyle changes.

2. Depression as a symptom
   
   

• • Depression can also appear as a symptom of another medical condition rather than a standalone disease. Examples consist of:
    • Neurological disorders: Parkinson’s disease, Alzheimer’s disease, stroke.
    • Endocrine disorders: Hypothyroidism, Cushing’s syndrome.
    • Chronic illnesses: Cancer, diabetes, heart disease.
    • Nutritional deficiencies: Low vitamin D, B12, or iron.
    • Substance use disorders: Alcohol or drug withdrawal.
  • Treating the underlying cause can help alleviate the depressive symptoms in these cases.

Why is depression more commonly a symptom?

1. Reaction to life events
   
   
   • Many people experience depressive symptoms due to stress, grief, trauma, or significant life changes, such as job loss, divorce, or the death of a loved one.
   • This type of depression is often situational and temporary, resolving once the stressor is managed.
2. Medical conditions and hormonal changes
   • Depression is frequently a symptom of other illnesses, such as:
     • Thyroid disorders (hypothyroidism).
     • Chronic pain conditions (fibromyalgia, arthritis).
     • Neurological diseases (Parkinson’s, Alzheimer’s).
     • Autoimmune diseases (lupus, multiple sclerosis).
     • Hormonal shifts (postpartum depression, menopause, PMS).
   • Curing the underlying condition often improves the depressive symptoms.
3. Substance use and medications
   • Alcohol and drug withdrawal can cause fleeting depressive symptoms.
   • Some medications (corticosteroids, beta-blockers, hormonal birth control) list depression as a possible side effect.

When is depression a disease?

1. If depressive symptoms persist for weeks or months without an obvious cause, it may be major depressive disorder (MDD) or another clinical depressive disorder.
2. MDD is a chronic condition that requires treatment (therapy, medication, or both).
3. Unlike situational or secondary depression, MDD doesn’t always have a clear external trigger and is often linked to brain chemistry, genetics, and long-term stress.

Conclusion

• If depression is persistent and meets clinical diagnostic criteria, it is a disease (MDD or another depressive disorder).
• If depression is a temporary response to another condition (like hypothyroidism, grief, or chronic pain), it is a symptom.
• Depression as a symptom is more common and often linked to external factors or medical conditions.
• Depression as a disease (MDD) is less widespread but more serious and persistent.