levothyroxine and omeprazole

Pharmacokinetic: omeprazole reduces gastric acid secretion, which increases gastric pH. Levothyroxine absorption from the gastrointestinal tract is partially dependent on an acidic environment, so reduced acidity can decrease the solubility and absorption of levothyroxine.

Reduced levothyroxine absorption may lead to lower serum thyroxine levels and elevated TSH, potentially causing clinical hypothyroidism. Patients may experience fatigue, weight gain, cold intolerance, or worsening of hypothyroid symptoms, particularly if on stable levothyroxine therapy.

Monitor serum TSH and free T4 levels after initiating or discontinuing omeprazole, especially in patients on long-term levothyroxine. Advise patients to take levothyroxine at least 4 hours apart from omeprazole if possible, although gastric pH effects may persist. Adjust levothyroxine dose based on thyroid function tests. Consider alternative acid-suppressants if clinically appropriate, or increase monitoring frequency.

Well-established interaction supported by clinical studies and case reports. The extent of interaction varies with the dose and duration of omeprazole therapy.