What Are the Ingredients of Levothyroxine?

The primary ingredient of levothyroxine is synthetic T-4, which is identical to the hormone produced in the thyroid gland. Levothyroxine also contains inactive ingredients common in prescription medications. These inactive ingredients don't alter its effectiveness but add color, enable a longer shelf life and increase efficiency in manufacturing the medication.

In addition to synthetic T-4, levythyroxine contains eight inactive ingredients plus color additives. Color additives vary depending on the dose being manufactured. The inactive ingredients include butylated hydroxyanisole, a food antioxidant, microcrystalline cellulose, sodium lauryl sulfate, sucrose and magnesium stearate. Magnesium stearate is a powder that can be added to other powders to make them flow more easily, which assists in the manufacture of levythyroxine. The Food and Drug Administration must approve the inactive ingredients in levythyroxine and in all prescription drugs.

Levythyroxine supplements the hormone produced by the thyroid gland, which helps regulate the human body's energy level and the rate at which it metabolizes food. It is also prescribed to prevent a goiter, which is an enlargement of the thyroid gland. Levythyroxine should not be used to help in weight loss and should not be taken by individuals on medications related to losing weight. In these cases, levythyroxine can be life-threatening.