The following is an overview of the key forms of thyroid hormone replacement.
Levothyroxine (Synthetic Thyroxine/T4)
Among conventional physician circles, the most popular and commonly prescribed thyroid hormone replacement drug is levothyroxine, a synthetic form of thyroxine (the thyroid hormone abbreviated as T4). Levothyroxine is also referred to as l-thyroxine.In the United States, levothyroxine is available as generic levothyroxine, as well as brand names Synthroid, Levothroid, Levoxyl, and Unithroid. In Canada, Synthroid, Eltroxin, and PMS-Levothyroxine are popular brand names.
Many doctors do not recommend generic levothyroxine. Brand names are preferred, and each is generally considered equally effective.
Liothyronine (Synthetic Triiodothyronine/T3)
The thyroid gland manufacturers both thyroxine and triiodothyronine (T3), the active form of thyroid hormone. Liothyronine is a synthetic form of T3, and it is available in a manufactured form as the brand Cytomel. T3 can also be compounded.In recent years, some practitioners have been prescribing T3 in addition to T4. One prominent study published in the New England Journal of Medicine found that patients benefited from this treatment. Some other studies have failed to demonstrate a benefit. The use of T4/T3 combination treatments remains controversial.
Liotrix (Synthetic Thyroxine/Triiodothyronine T4/T3 Combination)
Liotrix is a synthetic combination of thyroxine and triiodothyronine (T4 and T3). Liotrix is available in a manufactured form, known by the brand name Thyrolar.Desiccated Natural Thyroid
Desiccated thyroid is a drug prepared from dried porcine (pig) thyroid. Desiccated thyroid was the only thyroid drug available in the early 1900s, until levothyroxine was introduced in the 1950s. Natural thyroid fell out of favor as the synthetic product was touted as more modern and stable. Since the 1990s, desiccated thyroid has enjoyed a resurgence, primarily with older doctors and holistically-oriented physicians who claim that it resolves symptoms better than synthetics in some patients.Today, several brands of desiccated thyroid are available by prescription, including Armour Thyroid, the most popular brand, as well as Nature-throid and Westhroid.
Sources
Braverman, MD, Lewis E., and Robert D. Utiger, MD. Werner and Ingbar's The Thyroid: A Fundamental and Clinical Text. 9th ed. Philadelphia: Lippincott Williams & Wilkins (LWW), 2005.Shomon, Mary. Living Well With Hypothyroidism: What Your Doctor Doesn't Tell You...That You Need to Know. 2nd ed. New York. HarperCollins. 2005.
