People who have an underactive thyroid or other thyroid problems may benefit from Levothroid. This prescription medication is a synthetic version of a naturally occurring hormone in the body called levothyroxine. Levothroid works by boosting the thyroid hormone levels in the body. It comes in tablet form and is typically taken once a day. Possible side effects include insomnia and hair loss.
Levothroid is manufactured by Forest Pharmaceuticals, Inc.
How Does Levothroid Work?
Although it is synthetic, Levothroid is identical to the naturally occurring thyroid hormone levothyroxine (also known as T4). In addition to T4, the thyroid gland makes another thyroid hormone, known as triiodothyronine (T3). Usually, the thyroid gland produces much more T4 than T3 (however, T3 is much more active than T4). The body can convert the less-active T4 hormone into more of the T3 hormone as necessary. If your thyroid does not make enough thyroid hormones, there are a few different ways to increase your levels.
Some forms of thyroid replacement combine both T3 and T4 (such as natural thyroid replacement made from pig thyroids). However, because the body converts T4 into T3 as needed, most people can successfully take just T4. Alternatively, just T3 can be taken. Currently, most people just take T4 products, such as Levothroid.
Written by/reviewed by: Kristi Monson, PharmD;Arthur Schoenstadt, MD
Last reviewed by: KristiMonson, PharmD;
List of references (click here):
Levothroid [package insert]. St. Louis, MO: Forest Pharmaceuticals, Inc.;2005 September.
Food and Drug Administration, Center for Drug Evaluation and Research. Electronic orange book: Approved drug products with therapeutic equivalence evaluations. FDA Web site. Available at: http://www.fda.gov/cder/ob/. Accessed December 5, 2007.
Briggs GG, Freeman RK, Yaffe SJ. Drugs in Pregnancy and Lactation. 7th ed. Philadelphia (PA): Lippincott Williams & Wilkins;2005.
National Library of Medicine (US). Drugs and Lactation Database (LactMED). NLM Web site. Available at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT. Accessed December 5, 2007.
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