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Thyroid hormone replacement is the single most frequently prescribed medication in the United States and in many other countries, but people who have thyroid disease usually harbor misconceptions about what the thyroid is and what it does.

Do you take medication for thyroid disease? If you do, you are not alone. Just in the United States, nearly 25 million prescriptions for thyroid hormone replacement medication are filled every year.

Millions of people take thyroid hormone, but most people who take it (and occasionally their doctors) don't really know why. The American College of Endocrinology, a physician group, has taken on the task of educating people about thyroid disease and treatment.

Here, in question and answer form, is the most essential information for every thyroid disease patient. We'll start with the questions established patients are most likely to ask.

Q. What can go wrong with thyroid medication?

Thyroid medication is not a perfect replacement for natural thyroid hormone. Thyroid replacement hormone is a form of thyroid hormone that the body usually keeps in storage. It isn't the "activated" form of the hormone. Sometimes your body will convert your thyroid medication into the useful form of thyroid hormone faster and sometimes it will convert it more slowly.

For patients who have hypothyroidism but still have a poorly functioning thyroid, there is an additional complication. The pituitary gland in the brain releases a compound called thyroid stimulating hormone, or TSH. In turn, TSH triggers the production of thyroid hormone by the thyroid, which has to be further converted to be actually used. The pituitary may make more or less of the TSH that drives the production of thyroid hormone. Your doctor is more likely to measure TSH, the thyroid stimulating hormone, than T4 and T3, the actual thyroid hormone.

Where patients get into trouble is switching brands of thyroid hormone just because their bodies aren't making the right amount of TSH. It's important to change the dosage of medication, not the brand of medication. Tiny differences between different generics and different brand-name medications make it difficult for the body to make the right amount of TSH. If you switch brands, your body may also change its production of TSH, so your active hormone levels go high or low. The only way to avoid this is to stick with the brand of thyroid hormone you are current taking, letting your doctor adjust the dosage. It is important to make sure that your pharmacist does not switch brands of thyroid replacement hormone without your doctor's consent.

Q. Should I be using "natural" thyroid hormone replacement?

One of the issues with thyroid hormone replacement is that most medications are in the form of T4, also known as thyroxine or 3,5,3',5'-tetraiodothyronine. This is the form of thyroid hormone that the thyroid makes. The form of the hormone the body uses is T3, also known as triiodothyronine or (2S)-2-amino-3- [4-(4-hydroxy-3-iodo-phenoxy)- 3,5-diiodo-phenyl]propanoic acid. Three different kinds of enzymes convert the storage form of thyroid hormone, T4, into the active form of thyroid hormone, T3. When there is a malfunction of the thyroid gland, or it has been removed, most endocrinologists believe, it is better to replace the form of they hormone made by the thyroid itself and to rely on existing enzyme systems to convert it.

Not everyone, however, has the enzymes to convert T4 to T3. "Natural" thyroid hormone, such as Armour (not "armor") Thyroid, made from pig glands, contain both T4 and T3. So why shouldn't everybody use it? It's easier to get too much "natural" thyroid hormone replacement than synthetic. Your doctor needs to monitor your TSH and thyroid hormone levels along with your general state of health more closely if you use Armour Thyroid.

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  • Nainggolan, L. Thyroid Disease: 10 Questions Patients Should Ask. Medscape Medical News. 21 January 2015.Photo courtesy of Trekkyandy via Flickr:
  • Photo courtesy of paul.kenjerski via Flickr: