Endocrine System Home > Cytomel

Cytomel is a prescription drug used to treat an underactive thyroid and various other thyroid problems. It can also be used in certain thyroid diagnostic tests. Cytomel, which is a synthetic version of a naturally occurring thyroid hormone, comes in tablet form and is generally taken once daily. Potential side effects of the medication include headache, sweating, nervousness, and irritability.

What Is Cytomel?

Cytomel® (liothyronine sodium) is a prescription medication that is a manufactured version of a certain thyroid hormone. Even though it is synthetic, Cytomel is identical to the naturally occurring hormone liothyronine (also known as T3 or triiodothyronine). It is approved to treat an underactive thyroid (known medically as hypothyroidism) and goiters. Cytomel is also used in certain thyroid diagnostic tests.
(Click Cytomel Uses for more information on what the medication is used for, including possible off-label uses.)

Who Makes It?

Cytomel is manufactured by King Pharmaceuticals, Inc.

How Does It Work?

The thyroid gland makes two different thyroid hormones: levothyroxine (T4) and triiodothyronine (T3). Although T3 is much more active than T4, the thyroid usually produces more T4 than T3. 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 options to increase your levels.
Some forms of thyroid replacement combine T4 and T3 (such as natural thyroid replacement made from pig thyroids). However, such products are usually not the preferred option for most people. Synthetic (manufactured) thyroid hormones like Cytomel are less likely to cause allergic reactions, since they are not made from animal thyroids, and may provide for more precise control of thyroid levels. Although most people take a synthetic T4 thyroid replacement product (such as Synthroid®), some people may benefit from T3 replacement (such as Cytomel), either alone or in combination with a T4 medication. Some people may not convert T4 into T3 appropriately, in which case a T3 product (like Cytomel) would work better.
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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