Lethargy: Causes, Symptoms, and When to See a Doctor for Persistent Exhaustion

Lethargy = profound, persistent fatigue with reduced alertness, motivation, and activity tolerance. Not relieved by rest.

Common Causes

• Medical: Anemia, hypothyroidism, diabetes, heart failure, COPD, CKD, liver disease, infections (mono, TB, HIV), cancer.
• Medications: β-blockers, antihistamines, opioids, benzodiazepines, antidepressants, antihypertensives.
• Psychiatric: Depression, anxiety, burnout, somatic symptom disorder.
• Lifestyle: Sleep deprivation, poor diet, sedentary, alcohol/substance use.
• Endocrine: Adrenal insufficiency, hypogonadism.

Red Flags (Urgent)

• Sudden onset, fever, weight loss, night sweats, focal weakness, confusion, syncope.

Evaluation: history, exam, CBC, CMP, TSH, ferritin, B12, folate, ESR/CRP, UA, CXR, EKG. Targeted workup based on clues.