This narrative review examined how Ramadan fasting — a month of dawn-to-sunset food and fluid restriction — affects thyroid hormone levels in healthy adults and those with thyroid disorders. Pooled evidence suggests that healthy individuals maintain normal hypothalamic-pituitary-thyroid axis function throughout Ramadan. Hypothyroid patients on levothyroxine may experience a modest rise in TSH after fasting, likely linked to shifts in medication timing, sleep disruption, and circadian changes rather than fasting alone. Free T4 generally stays stable. No single levothyroxine dosing schedule proved superior. For hyperthyroid patients, evidence is scarce and recommendations rely largely on expert opinion. The authors conclude that most stable thyroid patients can safely fast with appropriate monitoring and personalized guidance.
