5 known interactions • 0 major • 4 moderate • 1 minor
Always disclose all medications to your healthcare providers — prescription medicines, OTC medications, vitamins, and herbal supplements. This list may not include every possible interaction. Use our Medicine Interaction Checker to screen your complete medication list.
Potentially life-threatening or causing permanent damage. Avoid combination.
May worsen condition or require dose adjustment. Monitor closely.
Usually limited clinical effect. Manage with routine monitoring.
Calcium carbonate / antacids / iron supplements
Calcium and iron bind levothyroxine in the GI tract, reducing absorption by up to 40%.
Management: Take levothyroxine 4 hours apart from calcium, iron, antacids, and proton pump inhibitors.
Warfarin
Thyroid hormones enhance the anticoagulant effect of warfarin by increasing catabolism of clotting factors.
Management: Monitor INR closely when initiating or changing levothyroxine dose.
Digoxin
Thyroid status affects digoxin requirements. Hypothyroid patients need lower digoxin doses; restoration of euthyroidism may require dose adjustment.
Management: Monitor digoxin levels and cardiac status with thyroid dose changes.
Rifampin / phenytoin / carbamazepine
Hepatic enzyme inducers accelerate levothyroxine metabolism, reducing T4 levels and potentially causing hypothyroidism.
Management: Monitor TSH and adjust levothyroxine dose as needed.
Estrogens (OCP, HRT)
Estrogens increase TBG (thyroxine-binding globulin), increasing T4 requirements in hypothyroid patients.
Always ask your pharmacist about potential interactions with food, alcohol, and supplements specific to Levothyroxine. Some medicines have significant interactions with grapefruit juice, high-fat meals, dairy products, or vitamin K-rich foods.