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  • Anonymous
      Post count: 93172

      I know this is long, but when I found it, I also found it most interesting. Most of us take our medication and then we also take calcium supplements to prevent bone density loss and osteoporosis. This letter was in the March 11, 1998 Journal of the American Medical Association (JAMA):

      “Letters – March 11, 1998

      Calcium Carbonate and Reduction of Levothyroxine Efficacy

      To the Editor.—I would like to report an interaction between 2 commonly prescribed drugs, levothyroxine sodium and calcium carbonate, which reduces levothyroxine efficacy. This inhibition may be reversed by separating the administration of these 2 medications.

      In a recent evaluation of 3 women with thyroid cancer who were receiving levothyroxine to suppress serum thyroid-stimulating hormone (TSH) levels, it was noted that simultaneous ingestion of some calcium formulations reduced levothyroxine effectiveness (Table). For example, patient 1 took levothyroxine (125 µg/d) and had a baseline serum TSH concentration of 0.08 mU/L (normal, 0.5-4.0 mU/L). She subsequently began to take calcium carbonate (in the form of Tums) for prevention of osteoporosis, often taking it together with levothyroxine. She experienced fatigue and a 4.5-kg weight gain over the next 5 months, and her serum TSH level was found to have risen to 13.3 mU/L. She then stopped taking calcium carbonate but maintained her levothyroxine regimen. Three weeks later her serum TSH level had declined to 0.68 mU/L.

      In patients 2 and 3 (Table), there was also loss of efficacy of levothyroxine when it was taken simultaneously with oyster shell calcium carbonate (in the form of Os-Cal). In both patients, levothyroxine activity was restored by administering it in the morning and administering calcium carbonate after lunch and dinner. Interestingly, patient 3 previously took a different form of calcium carbonate (Giant brand) with levothyroxine without affecting TSH suppression.

      Decreased bioavailability induced by simultaneous intake of other medications (eg, aluminum-containing antacids, iron, cholestyramine, sucralfate) is a well-known occurrence with levothyroxine therapy.[1] Decreased absorption could similarly account for the calcium carbonate effect. Calcium carbonate itself or, alternatively, excipients or contaminants in the preparation[2] could form insoluble chelates with levothyroxine.[3] Differences in excipients or contaminants or variations in rates of dissolution[2] could explain the discrepant effects of the 2 calcium carbonate preparations used by patient 3.

      Given that both calcium and levothyroxine are used together in a large number of patients, this phenomenon is likely to be widespread. Special attention should be directed toward postmenopausal women, as these individuals most frequently use calcium supplements to prevent osteoporosis and, in addition, often require therapy with levothyroxine.[4] Separating administration of these medications by at least 4 hours should provide a simple method for maintaining levothyroxine efficacy.

      Christine R. Schneyer, MD
      Sinai Hospital of Baltimore
      The Johns Hopkins School of Medicine
      Baltimore, Md

      I thank Pnina Schwartz, RN, for assistance in evaluating these patients; Ralph Shangraw, PhD, Stephen Sherman, MD, and Paul Englund, PhD, for valuable discussions; and David Cooper, MD, for much advice and encouragement.


      1. Sherman SI, Malecha SE. Absorption and malabsorption of levothyroxine sodium. Am J Ther. 1995;2:814-818.

      2. Levenson DI, Bockman RS. A review of calcium preparations. Nutr Rev. 1994;52:221-232.

      3. Kendall EC, Osterberg AE. The chemical identification of thyroxin. J Biol Chem. 1919;40:265-334.

      4. Kaufman SC, Gross TP, Kennedy DL Thyroid hormone use: trends in the United States from 1960 through 1988. Thyroid. 1991;1:285-291.

      (JAMA. 1998; 279:750)”

      Jan, Nancy, someone on the board, could you ask our medical experts about this please? I would like to know.


      Mitakuye Oyasin,

        Post count: 93172

        RAI did a good job nuking my thyroid, and I am finally (and sadly) a hypo. No fun with it. I felt fine and alert despite the very high TSH level, but I was advised to start taking levothyroxine.

        Eltroxin (Canada and no junk in it)has left me rather dopey almost all the time. When I was on 50 mcg, I experienced pains in joints and muscles (spine, forearms, wrists, and shoulders) and sleepiness in the mornings. When I upped to 100 mcg two weeks later as instructed, pain in muscles and joints disappeared, but I am sleepy almost all the time.

        My endo is away until next week. My endo appointment is on Halloween!

        Does it mean I am on tooooo much levothyroxine????? It looks as if 75mcg sounds better for me??? Can’t split those 100 mcg in quarters!!! Would appreciate hearing suggestions from you hypo Graves warriors…

          Post count: 93172

          Hi Belinda,
          Welcome back.
          As a suggestion even though your endo is away even if you do not feel good
          perhaps you can ask the endo nurses’ to let you go get your bloodwork done
          that is the only way they can tell along with listening to your symptoms. Do
          Based on what the bloodwork shows they can up your “L.” It is not
          good to remain hypo for a period of time if you feel you are.
          So, good luck to you.


            Post count: 93172

            Dear Belinda
            Just wanted to post and tell you I am from canada too ,and I get exactly the same side effects as you do taking that stuff,meaning that I could not have written and described it any better then you did,strange drug eh,take care Barb little warrior

              Post count: 93172

              I understand the levothyroxine have iodine in them. I had an allergic reaction to I-131 (RAI)….. I just started the levothyroxine today…is there any chance I will be allertic to the levothyroxine?

                Post count: 93172

                Hi, DMB:

                I guess noone can tell you for sure, but the long odds are that you should not be allergic to this pill. Iodine is THE important ingredient in thyroid hormone. It exists (or existed) in your body’s own thyroid hormone prior to you becoming ill. You have been taking up iodine (in the food you eat) all of your life, and your thyroid has been turning it into thyroid hormone. Without iodine, the thyroid could not make thyroid hormone. Levothyroxin is CHEMICALLY IDENTICAL to your body’s naturual T4 — thyroxin, which contains four atoms of iodine. So while occasionally someone is allergic to their thyroid replacement hormone, it is not the iodine in the compound that is the problem — it is some other ingredient that has been used to make the chemical into a pill. And often it is the dye used to distinguish one dosage from another. These pills also come without dyes for those people who are allergic to the dyes.

                Bobbi — NGDF Online Facilitator

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