Thyroid Preparations/Selected Chelation Agents Interactions

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

Aluminum, calcium, iron, lanthanum, magnesium, simethicone, and sucralfate decreases the amount of thyroid medicine your body absorbs.

What might happen:

Your thyroid medicine may not work as well. Signs and symptoms to look for include: feeling tired, dry skin and brittle nails, not being able to stand the cold, constipation, and depression.

What you should do about this interaction:

Try to time your medicines so that you take your thyroid medicine at least 4 hours from may medicines that contain aluminum, calcium, iron, magnesium, simethicone, or sucralfate or at least 2 hours from lanthanum. If you have any questions about how to schedule your medicines, ask your pharmacist.If you experience fatigue, sluggishness, constipation, stiffness, muscle cramps, loss of appetite, weight gain, dry skin, or difficulty in cold weather, contact your doctor.Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. Your doctor may want to check you thyroid function test to see if you are getting the right amount of thyroid medicine.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

View Reference
  • 1.Synthroid (levothyroxine sodium) US prescribing information. Abbott Laboratories February, 2024.
  • 2.Fosrenol (lanthanum carbonate) US prescribing information. Shire US Inc. May, 2020.
  • 3.Zamfirescu I, Carlson HE. Absorption of levothyroxine when coadministered with various calcium formulations. Thyroid 2011 May;21(5):483-6.
  • 4.Campbell NR, Hasinoff BB, Stalts H, Rao B, Wong NC. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med 1992 Dec 15;117(12):1010-3.
  • 5.Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA 2000 Jun 7;283(21):2822-5.
  • 6.Schneyer CR. Calcium carbonate and reduction of levothyroxine efficacy. JAMA 1998 Mar 11;279(10):750.
  • 7.Phansalkar S, van der Sijs H, Tucker AD, Desai AA, Bell DS, Teich JM, Middleton B, Bates DW. Drug-drug interactions that should be non-interruptive in order to reduce alert fatigue in electronic health records. J Am Med Inform Assoc 2012 Sep 25.
  • 8.Sherman SI, Tielens ET, Ladenson PW. Sucralfate causes malabsorption of L-thyroxine. Am J Med 1994 Jun;96(6):531-5.
  • 9.Liel Y, Sperber AD, Shany S. Nonspecific intestinal adsorption of levothyroxine by aluminum hydroxide. Am J Med 1994 Oct;97(4):363-5.
  • 10.Havrankova J, Lahaie R. Levothyroxine binding by sucralfate. Ann Intern Med 1992 Sep 1;117(5):445-6.
  • 11.Vick K, Wennerberg P. Sucralfate-levothyroxine drug interaction..
  • 12.Sperber AD, Liel Y. Evidence for interference with the intestinal absorption of levothyroxine sodium by aluminum hydroxide. Arch Intern Med 1992 Jan;152(1):183-4.
  • 13.Phoslyra (calcium acetate) US prescribing information. Fresenius Medical Care North America April, 2015.
  • 14.Mersebach H, Rasmussen AK, Kirkegaard L, Feldt-Rasmussen U. Intestinal adsorption of levothyroxine by antacids and laxatives: case stories and in vitro experiments. Pharmacol Toxicol 1999 Mar;84(3):107-9.
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CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.