Thyroid Hormone Medication Interactions: What You Need to Know

Thyroid hormone replacement (e.g., levothyroxine) interacts with many drugs and supplements, potentially altering effectiveness or causing side effects. Key interactions include:

Medications That Increase Thyroid Hormone Levels/Effects

• Amiodarone (antiarrhythmic) – contains iodine, can cause hypo- or hyperthyroidism.
• Estrogens (oral contraceptives, HRT) – raise thyroid-binding globulin, increasing total hormone levels; may require dose adjustment.

Medications That Decrease Absorption

• Calcium supplements, iron, antacids (aluminum/magnesium), cholestyramine/colestipol, proton pump inhibitors (PPIs) – take thyroid hormone 4 hours apart.
• Soy products (high intake) – may impair absorption.

Medications That Alter Metabolism/Clearance

• Rifampin – accelerates breakdown, reducing effectiveness.
• Phenobarbital, carbamazepine, phenytoin – similar enzyme induction.

Medications With Altered Effects Due to Thyroid Hormone

• Warfarin – thyroid hormone increases catabolism of clotting factors; INR monitoring needed.
• Beta-blockers – can mask tachycardia of hyperthyroidism.
• Digoxin – hypothyroidism increases digoxin levels; hyperthyroidism decreases them.
• Insulin/oral hypoglycemics – thyroid status affects glucose metabolism.
• Lithium – can cause hypothyroidism or goiter.
• Sertraline – may alter thyroid hormone metabolism.

Always inform your prescriber of all medications, supplements, and herbal products to ensure proper monitoring and dose adjustments.