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.

What Is Levothroid?

Levothroid® (levothyroxine sodium) is a prescription thyroid medication. It is approved to treat an underactive thyroid (known medically as hypothyroidism) and to treat a variety of thyroid problems, including certain types of thyroid cancer. The medication is actually a synthetic version of a certain type of thyroid hormone.
(Click Levothroid Uses for more information, including possible off-label uses.)

Who Makes It?

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.
Last reviewed by: Kristi Monson, PharmD
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