Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. Thyroid hormone is a chemical messenger used by the brain to control many functions in the body including metabolism, which is how the cells use energy. The standard treatment for hypothyroidism is hormone replacement therapy.
About T3 and T4
The thyroid gland produces two main types of thyroid hormone which are known as T3 (triiodothyronine) and T4 (tetraiodothyronine). These two hormones control your body’s metabolism. Being low on thyroid hormone means your metabolism is slower than normal. This can affect how your heart beats, how you process food, how your body handles heat, and how well you can think.
The basic hormone produced by the thyroid gland is T4. When T4 enters your bloodstream and interacts with other chemicals it releases one iodine atom and becomes T3. T3 is generally the more active and stronger thyroid hormone. T3 carries messages from the brain to other cells to regulate the metabolism.
Hypothyroidism treatment provides extra thyroid hormone to the body. If your thyroid is still functioning but not keeping up, your hormone replacement dose may be lower than if your thyroid is not functioning at all. The U.S. Food and Drug Administration (FDA) regulates thyroid hormone replacements, which are only available by prescription.
Your doctor will prescribe the lowest dose possible to bring your hormone level into the normal range. Too much thyroid hormone replacement can cause other symptoms, including irregular heartbeat.
Synthetic thyroid replacement
Thyroid hormone replacement is available as a synthetic (lab-created) hormone which is most commonly called levothyroxine. This is considered by many to be the standard hypothyroidism treatment. Levothyroxine contains only the T4 hormone.
Proponents of synthetic replacement believe the body will convert T4 to T3 to complete the replacement process. Manufacturers claim that synthetic T4 is identical to the hormone produced by the human thyroid gland and claim it is superior to animal hormone replacements because the dose is more consistent.
The FDA has approved 6 brands of synthetic T4 replacement:
• Levothyroxine Sodium
Although all these brands of T4 are considered to be identical to human thyroid, they do not all provide the exact same dose. If you begin treatment with one brand of this drug, do not change brands without consulting with your doctor so your dose can be monitored and adjusted if necessary.
Animal thyroid replacement
Animal thyroid replacement is created from the thyroid gland of certain animals. One common brand of animal replacement, Nature-Throid, contains both T3 and T4 hormone. The manufacturer claims this is preferable because natural hormone is more readily recognized by the body and may receive a more favorable response. They believe it is better to replace both T3 and T4 rather than just T4 in case the body is unable to convert T4 to the needed T3.
The manufacturer says Nature-Throid complies with all FDA standards. They say the drug is tested to maintain strict potency and consistency and has never been recalled for inconsistent levels.
Whether you are prescribed synthetic or animal hormone replacement, it is important to take the medication as directed. Do not take thyroid hormone replacement with food, or at the same time that you take certain medications including multivitamins, calcium, and antacids.
Hypothyroidism is diagnosed using blood tests to measure the amount of thyroid hormone or thyroid stimulating hormone in your system. Once thyroid hormone replacement therapy begins, your doctor will need to continue to check your thyroid levels to establish the best dose for your treatment and to make sure that dose continues to be effective.
Medline Plus. Hypothyroidism. Web. December 21, 2011.
Endocrine Web. What Is Thyroid Hormone Replacement Therapy?.. Eren Berber, MD. Web. December 21, 2011.
Endocrine Web. Synthetic T4 Supplements for Hypothyroidism. Eren Berber, MD. Web. December 21, 2011.
Endocrine Web. Animal Thyroid Supplements for Hypothyroidism. Eren Berber, MD. Web. December 21, 2011.
Medicine Net. Hypothyroidism. Ruchi Mathur, MD, FRCP(C). Web. December 21, 2011.
Nature-Throid. Nature-Throid ™ vs. Synthetic Thyroid. Web. December 21, 2011,
Reviewed December 22, 2011
by Michele Blacksberg RN
Edited by Jody Smith