What Vitamins or Foods Interfere with Synthroid?

  • Medical Author:
    Ruchi Mathur, MD, FRCP(C)

    Ruchi Mathur, MD, FRCP(C) is an Attending Physician with the Division of Endocrinology, Diabetes and Metabolism and Associate Director of Clinical Research, Recruitment and Phenotyping with the Center for Androgen Related Disorders, Department of Obstetrics and Gynecology at Cedars-Sinai Medical Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Ask the experts

I had my thyroid removed and have been using Synthroid for almost 30 years with no problem. What foods or vitamins (for example iron) interfere with the absorption of Synthroid?

Doctor's response

Aluminum and magnesium containing antacids, calcium carbonate, simethicone, or sucralfate and iron-containing compounds may decrease the absorption of Synthroid; so you should not take these medications within four hours of taking Synthroid. Agents that bind cholesterol such as cholestyramine have the same effect and should also not be taken apart from the Synthroid.

Antidepressants may increase the effects of Synthroid, and the dosage may need to be adjusted.

In regard to foods and herbs, while nothing is off limits in most cases, it is reasonable to limit intake of goitrogenic foods (for example, asparagus, cabbage, peas, turnip greens, broccoli, spinach, brussel sprouts, lettuce, soybeans). Soybean flour (infant formula), cottonseed meal, walnuts, and dietary fiber may also decrease absorption of Synthroid from the GI tract.

While this is not a complete list, it gives you an idea of interactions you may need to consider. For these reasons it is recommended that thyroid medication be taken on an empty stomach 30-60 minutes before meals or at least three hours afterward.

Thyroid Quiz: Test Your Medical IQ

Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care

REFERENCE:

"Levothyroxine"
MedlinePlus
U.S. National Library of Medicine

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Last Editorial Review: 7/6/2017

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