Synthroid is typically prescribed to treat an underactive thyroid and a variety of thyroid problems. This manufactured drug is identical to the naturally occurring hormone levothyroxine (T4). As with any medication, side effects are possible with Synthroid, such as insomnia, hair loss, and a rapid heart rate. The medication comes in tablet form and is taken once a day in the morning.
What Is Synthroid?
Synthroid® (levothyroxine sodium) is a prescription medication that is a manufactured version of a certain thyroid hormone. Even though it is synthetic, the drug is identical to the naturally occurring hormone levothyroxine (also known as T4). It is used to treat an underactive thyroid (known medically as hypothyroidism) and to treat a variety of thyroid problems (including certain types of thyroid cancer).
Brand-name Synthroid is made by Abbott Laboratories.
How Does It Work?
The thyroid gland makes two different thyroid hormones: levothyroxine (T4) and triiodothyronine (T3). Typically, the thyroid produces much more T4 than T3 (however, T3 is much more active than T4). The body can convert the T4 hormone into T3 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 T4 and T3 (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 (such as with Synthroid). Alternatively, just T3 can be taken (as products such as Cytomel®). Currently, most people take just T4 (such as Synthroid).
Written by/reviewed by: Kristi Monson, PharmD;Arthur Schoenstadt, MD
Last reviewed by: KristiMonson, PharmD;
List of references (click here):
Synthroid [package insert]. North Chicago, IL: Abbott Laboratories;2002 July.
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 November 6, 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 November 6, 2007.
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