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How to take Your Thyroid Drugs

Frequently Asked Questions about Food, Drug and Supplement Interactions

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Updated December 15, 2003

Q. How About "Goitrogenic" Foods Like Kale or Brussels Sprouts?

Goitrogenic foods like brussels sprouts, rutabaga, turnips, cauliflower, African cassava, millet, babassu (a palm-tree coconut fruit popular in Brazil and Africa) cabbage, and kale can act like the antithyroid drugs propylthiouracil and methimazole in disabling the thyroid function, so they should not be eaten in large amounts by someone on thyroid hormone replacement who still has a thyroid. It's thought that the enzymes involved in the formation of goitrogenic materials in plants can be destroyed by cooking, so thorough cooking may minimize goitrogenic potential.

Q. Is There a Problem with Antacids?

Antacids -- like Tums, or Mylanta, in liquid or tablet forms -- may delay or reduce the absorption of thyroid drugs, and therefore, should also be taken at least two hours apart from when you take your thyroid hormone.

Q. What About Calcium and Calcium-Fortified Orange Juice?

Like antacids, calcium can interfere with the absorption of thyroid drugs. You should take calcium at least two to three hours apart from taking your thyroid hormone. The same holds true for calcium-fortified orange or apple juice. You should not take your thyroid hormone at the same time as calcium-fortified juice.

Q. What about Over the Counter Drugs Like Cough Medicines, Cold Medicines, Decongestants?

Most packages of over-the-counter cough and cold medicines and decongestants say "Do not take if you have one of the following..." and then goes on to list thyroid disease. While you should always check with your doctor, it's generally understood that this warning is more applicable for people with hyperthyroidism (overactive thyroid) than hypothyroidism (underactive thyroid). Because these drugs contain stimulants, the logic is for someone with hyperthyroidism to avoid adding even further stimulation or strain on the heart from these drugs. That said, some people with hypothyroidism do find that they become sensitive to ingredients like pseudoephedrine, what you'd typically find in Sudafed or other decongestants. Some doctors will recomend you try only a partial dose, and see if you have a reaction, and only then try to work you way up to the normal dose and see if it bothers you.

Q. How Should You Take Vitamins with Iron?

Iron, whether alone, or as part of a multivitamin or prenatal vitamin supplement, interferes with thyroid hormone absorption. You should not take your vitamins with iron at the same time as your thyroid hormone, and should allow at least two hours between taking them.

Q. What About Thyroid Hormone and Estrogen? (i.e., Hormone Replacement Therapy, Birth Control Pills)

Women taking estrogen (either as hormone replacement -- i.e., Premarin -- or in birth control pills) may need to take more thyroid replacement hormone. Estrogen increases the body's production of a blood protein that binds thyroid hormone to it, making it inactive. For women without thyroids in particular, this can cause a need to increase the dosage level slightly, as there is no thyroid to compensate. After beginning any estrogen therapy, a woman should always have TSH tested to see if the estrogen is having an impact on overall TSH and thyroid function and might require a dosage adjustment.

Q. What Do You Need to Know About Some Other Prescription Drugs?

Antidepressants
Use of tricyclic antidepressants at the same time as thyroid hormones may increase the effects of both drugs, and may accelerate the effects of the antidepressant. Be sure your doctor knows you are on one before prescribing the other.

Insulin
Insulin and the similar oral hypoglycemic drugs for diabetes can reduce the effectiveness of thyroid hormone. Be sure your doctor knows you are on one before prescribing the other. If you're on insulin or an oral hypoglycemic, you should be closely watched during the initiation of thyroid replacement therapy.

Cholesterol-Lowering Drugs (Cholestyramine or Colestipol -- Colestrol, Questran, Colestid)
These cholesterol-lowering drugs bind thyroid hormones, and a minimum of four to five hours should elapse between taking these drugs and thyroid hormones.

Anticoagulants ("Blood Thinners")
Anticoagulant (blood thinning) drugs like Warfarin, Coumadin or Heparin can on occasion become stronger in the system when thyroid hormone is added to the mix. Be sure to mention to your doctor if you are on one or the other, and a new prescription is added.

Note: The above is NOT a complete list of all drugs that can interact with thyroid medicines. Talk to your pharmacist or doctor for more information.

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