How To Take Levothyroxine

by Sheldon Rubenfeld, M.D. Endocrinologist, Private Practice of Thyroidology, Endocrinology and Metabolism Clinical Professor, Baylor College of Medicine, Houston, Texas

Reprinted with permission from Dr. Rubenfeld's book Could It Be My Thyroid?
2nd edition, 2002, copyright 1996 and 2002 by Sheldon Rubenfeld.
3rd edition available through bookstores early in 2004.

The information contained on this web site is intended for educational purposes only. It is not intended, nor should it be interpreted, as medical advice or directions of any kind. Any person viewing this information is strongly advised to consult their own medical doctor(s) for all matters involving their health and medical care.

  • Levothyroxine should be taken daily unless directed otherwise.
  • If you miss a dose, you may “double up” the next day. If you miss more than one day, double up for as many days as necessary to catch up.
  • Levothyroxine is best absorbed when it is taken:
    • On an empty stomach
    • With water only
    • One hour before or two hours after eating
    • One hour before taking any medications, vitamins, or supplements
    • Two hours before taking iron or calcium
    • Twelve hours before taking Questran® or Colestid®

Nonprescription Drugs, Iodine, and Levothyroxine

The labels on some nonprescription cold and flu preparations state that the drugs should not be taken if patients have thyroid disease. This warning does not apply to patients taking levothyroxine in prescribed amounts.

There are, however, many over-the-counter preparations containing either iodine or thyroid hormones, or both, that will interfere with levothyroxine therapy and should not be taken. These preparations can both aggravate thyroid disorders and alter thyroid function test results. Consequently, problems arise when physicians prescribe levothyroxine based on misleading test results caused by over-the-counter products.

Unfortunately, over-the-counter iodine and thyroid supplements are readily available on the Internet, in health food stores, and in some grocery and drug stores. Many well-intentioned patients erroneously assume that supplementing their diets with natural products will help their thyroid problems; however, these products will not help. When patients search the Internet for information on thyroid disease, they are likely to see advertisements and links to sites selling natural products for thyroid dysfunction, weight loss, or energy. Very few sites list the ingredients or the amounts of the ingredients in these products. Therefore, patients cannot possibly know what they are taking – and neither can the physicians writing levothyroxine prescriptions.

Similarly, products from health food stores may not be adequately labeled. The labels on a variety of supplements contain terms such as “thyroid” or “thyro,” leading some consumers to assume the products contain thyroid hormone. A closer look will show that few of these supplements actually list thyroid tissue as an ingredient. If they do, the usually do not state the source or the amount of the thyroid hormone in the products. Typically, iodine from kelp is among the ingredients listed on the labels of these products. The recommendations stated on some labels may range from 450 to 600 mcg of iodine daily, well above the minimum 150 mcg of iodine recommended by the World Health Organization for nonpregnant adults. Since the average daily intake of iodine in the United States is already 300 to 500 mcg, supplementing the typical American diet with iodine is unnecessary and potentially harmful.

Iodine is also found in certain prescription medications. In most cases, there are iodine-free substitutes available for medications containing iodine; however, sometimes an iodine-free substitute is not available. For example, some patients cannot discontinue amiodarone, a very effective iodine-rich medication for control of dangerous hearth rhythm disturbances (arrhythmias). Some x-ray dyes also contain large amounts of iodine. These dyes can affect thyroid function test results and, occasionally, thyroid function for many months. CAT scans, arteriograms, intravenous pyelograms (IVPs), heart catheterizations, and myelograms are x-ray procedures that typically use injectable dyes with iodine.

In summary, patients should inform their physicians when they have had any procedures with iodinated dye within the preceding year. Furthermore, patients should not take over-the-counter products containing iodine or thyroid hormones but, if they do, they should tell their physicians.

Substances* Containing Iodine

  • amiodarone povidone- iodine douches
  • Cordarone® Bet adine® Medicated Douche
  • Pacerone® Ma ssengil® Medicated Douce
  • iodoquinol
  • Yodoxin® povidone- iodine topical ointments
  • Vytone® Betadine® ointment
  • kelp x-ray dyes
  • CAT scans
  • IVP’s
  • potassium iodide Myelograms
  • KI Syrup® arteriogram s
  • Pediacof Syrup®
  • Pima Syrup®
  • SSKI® (Lugol’s solution)

* This list contains some, but not all, of the substances containing iodine that may affect thyroid patients.

Last updated: October 23, 2006