Side Effects of Antithyroid Drugs

Antithyroid drugs are generally used to treat overactive thyroid (also called hypothyroid or Graves disease). This type of drug is intended to reduce or stop the production of hormones that are made by the thyroid, which is a butterfly-shaped gland located in the throat and wrapping around the voice box. Overactive thyroid can be diagnosed at any point in life and is an easily treatable disorder. In many cases, treatment for overactive thyroid is lifelong.

• Antithyroid drugs are used to treat overactive thyroids.

About

• According to Dr. Douglas Ross, antithyroid drugs are used to treat the effects of an overactive thyroid and the production of the two primary hormones that are produced by the thyroid gland. These hormones are known as T3 and T4 or thyroxin and triiodothyronine. It takes approximately six to eight weeks for the medications to take effect because they only treat the production of the hormones and do not address thyroid hormones already in a person's system. Antithyroid medications can be given in preparation for thyroid surgery and to treat hypothyroid and overactive thyroid during pregnancy.

Types

• Dr. Ross states that there are two different types of antithyroid drugs available in the United States at this time: MMI and PTU (methimazole and propylthiouracil). MMI is the preferred medication because it is faster acting and has fewer side effects. Generally MMI medication takes approximately six weeks to become effective and PTU takes approximately 17 weeks to become effective. After trying MMI medication with little effectiveness, a doctor may choose to prescribe PTU as a secondary attempt to address the overactive thyroid issues.

Minor Side Effects

• Dr. Ross indicates that the majority of individuals who take antithyroid medications have minor side effects that often disappear over time. These include hives, rashes, joint pain, low fever and joint swelling. Other side effects include changes in taste, nausea and vomiting. One method of addressing uncomfortable side effects is to change medications if the side effects are difficult to tolerate. Changes in taste, nausea and vomiting side effects depend on the dosage and may be eliminated by adjusting the dosage.

Major Side Effects

• In most cases, major side effects of antithyroid medications are extremely rare, according to Dr. Ross. One of the major side effects is agranularcytosis, which is a lowering in the production of white blood cells. Dr. Ross indicates that this is extremely rare and affects only approximately 1 out of every 200 to 500 individuals who take antithyroid medications. This side effect is likely to occur within the first three months of beginning to use the medication.

Rare Side Effects

• Dr. Ross indicates that three very rare possible side effects are liver damage, inability of the bone marrow to make blood cells and inflammation of the blood vessels. While these three side effects are extremely rare, it is important for a doctor to discuss them before beginning the medication so that a person knows what to look for should they occur.