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Thyroid Drugs
Frequently Asked Questions about Food, Drug and Supplement Interactions

by Mary Shomon

Many people ask about specific drugs, supplements and foods and whether or not you can take them when you're taking thyroid hormones. Here's a review of some of the current thinking. (Please note that this is by no means a comprehensive listing of all drug interactions, so be sure to ask for and read your patient insert that comes with your prescriptions, and always talk to your doctor and pharmacist regarding specific questions.)

Q. Should You Take Your Thyroid Hormone With Food vs. An Empty Stomach?

Food may delay or reduce the absorption of many drugs, including thyroid hormone. Food can often slow the process of the stomach entering, but it may also affect absorption of the drug you're taking by binding with it, by decreasing access to absorption sites, by altering the rate at which it dissolves, or by changing the stomach's pH balance. This is why many doctors recommend that for best absorption of your thyroid hormone, you should take it first thing the morning, on an empty stomach, one hour before eating.

Many doctors recommend that for best absorption of your thyroid hormone, take it first thing the morning, on an empty stomach, and wait one hour before eating, and at least two hours before taking any vitamin with iron.

However, if you cannot take it this way, consistency becomes the key. If you're going to take your thyroid hormone with food, take it every day with food, consistently. If you've changed from taking it on an empty stomach, then around six to eight weeks after you start taking it with food, you should have another TSH test to ensure you're receiving the proper amount of thyroid hormone. Taking the drug with food might inhibit absorption somewhat, but this safety check will make sure your dosage gets tweaked if it needs to be changed slightly. But again, CONSISTENCY. Don't take it some days with food, some days without, or you're sure to have erratic absorption, and it will be harder to regulate your TSH levels.

Q. What is the Impact of a High Fiber Diet?

Given that many people on thyroid replacement therapy are fighting an additional battle to lose weight, high fiber diets are also an issue. Anything that affects your digestion speed or speed of absorption of items into the stomach can have an effect on your absorption of thyroid hormone. Since high-fiber diets can, ahem, speed things up a bit, they are known to inhibit absorption for some people. So, should you forget about eating high-fiber? Absolutely not!!! Since the benefits of fruits, vegetables and a high-fiber diet are known, again, the issue here is consistency. If you are already eating a high-fiber diet regularly, and have regular TSH testing done, your dosage level is appropriate for you, given your diet. If you are starting a new regimen of eating high-fiber, plan to get tested around six to eight weeks after you change your diet, to make sure you're receiving the proper amount of thyroid hormone. But be consistent. Don't jump around, or you'll have erratic absorption, and that can wreak havoc on TSH levels...AND how you feel! But again, taking your thyroid hormone first thing a.m. on an empty stomach, and waiting at least an hour to eat, will ensure maximum absorption, whatever your diet is!

Q. What About Iodine and Kelp Supplements?

While some herbalists and vitamin proponents recommend iodine tablets or kelp supplements (which are high in iodine) for people with thyroid problems, you need to be extremely careful about any decision to take iodine or kelp supplements if you are on thyroid hormone replacement therapy.

The thinking behind taking iodine or kelp is that in many parts of the world, goiters and thyroid disease are related to iodine deficiency. In the U.S. and other developed countries, iodine deficiency is not very common anymore, due to the addition of iodine to salt -- iodized salt -- and other food products. In fact, the most common forms of thyroid disease found in the U.S. -- autoimmune thyroid diseases like Graves' Disease or Hashimoto's Thyroiditis -- have nothing to do with iodine deficiency at all. Actually, thyroids are extremely sensitive to iodine, and you need to be careful about adding too much iodine to the diet as it can irritate or aggravate the thyroid. Most doctors say not to worry about some iodized salt, or the iodine present in a food item such as an occasional sushi dinner. But even alternative nutritional doctor Stephen Langer, author of Solved: The Riddle of Illness, the follow-up book to Broda Barnes' Hypothyroidism: The Unsuspected Illness, advises against taking iodine or kelp supplements for people with autoimmune thyroid disease.

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?

Always check with your physician or pharmacist regarding any potential interactions of prescription drugs, herbs and supplements with your thyroid drugs. But some of the better known interactions include the following:

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.

Sticking Out Our Necks and this website are Copyright Mary Shomon, 1997-2003. All rights reserved. Mary Shomon, Editor/Webmaster
All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. You should seek prompt medical care for any specific health issues and consult your physician or health practitioner before starting a new treatment program. Please see our full disclaimer.