Thyroid/Iron Salts, Oral 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:

Iron may bind to your thyroid medicine in your stomach, preventing your body from absorbing your thyroid medicine.

What might happen:

Your thyroid medicine may not work as well.

What you should do about this interaction:

Do not take any products containing iron within four hours of taking your thyroid medicine. If you experience fatigue, sluggishness, constipation, stiffness, muscle cramps, loss of appetite, weight gain, dry skin, or difficulty in cold weather, contact your doctor. Your doctor may need to perform a blood test to make sure that your thyroid medicine is working.Your healthcare professionals (e.g. doctor or pharmacist) 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.

  • 1.Synthroid (levothyroxine sodium) US prescribing information. Abbott Laboratories June, 2011.
  • 2.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.
  • 3.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.