THYROID HORMONE REPLACEMENT
Thyroid hormone replacement drugs are drugs that provide the body with the thyroid hormone it needs to survive. Thyroid hormone replacement drugs are providing thyroid hormone that the thyroid gland itself cannot provide, for various reasons, including:
- hypothyroidism -- an underactive thyroid, which can be caused by various factors, including the autoimmune condition Hashimoto's disease, partial surgical removal of the thyroid, surgery to remove nodules, radioactive iodine treatment to the thyroid for Graves' disease or hyperthyroidism, or use of antithyroid drugs.
- nodules -- thyroid hormone replacement can shrink nodules and is sometimes used as a treatment
- goiter -- thyroid hormone replacement can shrink an enlarged thyroid known as a goiter in some cases, and is sometimes used as a treatment
- suppression -- thyroid hormone replacement in high doses is used after thyroid cancer treatment to totally suppress any remaining thyroid gland and prevent cancer recurrence
- preventive suppression -- in some people with thyroid antibodies but normal thyroid function, small doses of thyroid hormone replacement are used to prevent elevated antibodies and help prevent progression from Hashimoto's disease to full-fledged hypothyroidism
- In rare cases, thyroid hormone replacement drugs may be used in conjunction with antidepressants to aid in effectiveness of those drugs, or for other non-thyroid related uses, as determined by a physician.
There are a variety of different thyroid hormone replacement drugs.
Levothyroxine
Levothyroxine (or l-thyroxine) is the most commonly prescribed thyroid hormone replacement drug. It is a synthetic (man-made) form of the natural thyroid hormone thyroxine (also known as T4). Levothyroxine came into use for thyroid treatment in the 1950s, and was largely adopted as the primary thyroid hormone replacement drug, replacing the natural desiccated thyroid that had been used during the previous 50 year period.
A major controversy has surrounded the various levothyroxines, which as of August 2002, must go through and receive FDA approval under the FDA's "New Drug Application" process, in order to remain on the market. As of July 2002, Synthroid and Levothroid had NOT yet received FDA approval.
Another key controversy surrounding levothyroxine (T4) drugs is that they provide only one hormone. The human thyroid produces a variety of hormones, among them the two most important ones, T4 and T3. The T4 is converted by the thyroid and other peripheral organs into T3, and T3 is the active hormone that is actually used by the body at the cellular level. The assumption has been that in hypothyroidism, only T4 is needed, and that the body will convert T4 to T3 as needed. However, research has shown that the absence of T3 in thyroid hormone replacement treatments results in less satisfactory treatment, poorer quality of life, and worsened symptoms for the majority of patients. This has led to an increased use of natural desiccated thyroid products, additional synthetic T3, and synthetic producst that combine T4 and T3.
Liothyronine / Cytomel / T3 Drugs
Liothyronine (pronounced lye-oh-THYE-roe-neen) is a synthetic form of the T3 thyroid hormone. It is being more commonly added to levothyroxine treatment, to provide both T4 and T3 as part of the thyroid hormone replacement treatment.
In the U.S., the only brand of T3 available is Cytomel, manufactured by King Pharmaceuticals. Some compounding pharmacies can produce time-released capsules of liothyronine -- known as "Time-released T3" -- as a special order from your physician.
Liotrix / Thyrolar
Liotrix (pronounced LYE-oh-trix) is a synthetic drug that combines both levothyroxine and liothyronine (T4 and T3). The only brand of liotrix available in the U.S. is Thyrolar, manufactured by Forest Labs.
Natural Thyroid Drugs
These are prescription thyroid hormone replacement drugs that are made from the desiccated thyroid glands of pigs. (They are not, as some rumors claim, made from the thyroid gland of cows, and because they are made from U.S. grain-fed pigs, present a almost non-existent risk of "mad cow" disease.Natural dessicated thyroid drugs have been available since the late 1800s, but went out of favor in the 1950s, with the introduction of the heavily marketed synthetic levothyroxine. More recently, however, these drugs have become increasingly popular with patients and practitioners, in part because some patients feel better on these drugs.
WHICH THYROID DRUG IS BEST?
Which of the various thyroid drugs and combinations is best for you?
ANTITHYROID DRUGS
Antithyroid drugs are used for treatment of hyperthyroidism, to help slow down the thyroid's production of thyroid hormone, and reverse symptoms of an overactive thyroid. The two key types of antithyroid drugs are methimazole and propylthiouracil.
Methimazole
Methimazole (pronounced meth-IM-a-zole) known in the U.S. by the brand name Tapazole. Outside the U.S. it's sometimes known by the brand name Carbamizole.
Propylthiouracil
Propylthiouracil (pronounced proe-pill-thye-oh-YOOR-a-sill) is a generic drug in the U.S. In Canada, it can go by the brand name Propyl-Thyracil.
DRUGS FOR TESTING
Thyrotropin Alfa, which is known by its brand name, Thyrogen, is manufactured by Genzyme pharmaceuticals. This drug is used in follow-up of patients with well-differentiated thyroid cancer, as a way to scan/test for cancer recurrence without those patients having to withdraw entirely from all thyroid hormone and become hypothyroid.