The information provided here is meant to give you a general idea about each of the medicine groups listed below. Only the most general side effects are included, so ask your doctor if you need to take any special precautions. Use each of these medicines only as recommended by your doctor, and according to the instructions provided. If you have further questions about usage or side effects, contact your doctor.
Antithyroid medicines suppress thyroid activity. They are best suited for the treatment of Graves disease, an autoimmune cause of hyperthyroidism. The dose can be gradually reduced as the function of the thyroid decreases. It usually takes 6-8 weeks of treatment for the medicines to take effect and lower thyroid hormone to a healthy level. Until the treatment takes effect, your doctor may prescribe a beta-blocker (such as propranolol, atenolol, or metoprolol) to slow down the heart rate and relieve the jitters, sweating, and anxiety. When these symptoms subside, this beta-blocker can be reduced and then stopped.
About one month after you begin taking the antithyroid medicine, you will be asked to see your doctor for a repeat of the thyroid function tests and a review of your signs and symptoms. The dose of your antithyroid medicine may be changed based on the test results.
It usually takes 12-24 months of treatment before the thyroid produces a normal amount of thyroid hormone on its own. If hyperthyroidism goes into remission and your thyroid hormone levels return to normal, your doctor may decide to discontinue the medicine. However, some patients relapse when the treatment stops. People who have had severe hyperthyroidism, high levels of antibodies, and large goiters are most likely to relapse. But, it can happen to anyone. Therefore, all patients should see their doctor several times a year the first year after stopping treatment and at least annually thereafter.
The main antithyroid medicines are the thionamides:
- Methimazole (such as Northyx, Tapazole)
- Propylthiouracil (such as Propyl-Thyracil)
- Carbimazole (not currently available in the United States)
These drugs interfere with the thyroid gland’s ability to make hormones and with the peripheral tissues' ability to use it. These medicines can be taken with meals or on an empty stomach. It is important to always take them at the same time in relation to meals. Food affects the amount of medicine your body absorbs into the bloodstream. Therefore, always take your medicine with meals or always take it on an empty stomach.
Methimazole is the preferred drug of choice because of its reduced risk of adverse events. Another plus is that the medicine only needs to be taken once daily. Propylthiouracil is usually taken three times a day. This medicine is considered the second choice. But, if you are in your first trimester of pregnancy or if you cannot take methimazole, your doctor may have you take propylthiouracil. Carbimazole is yet another option to treat hyperthyroidism.
Possible side effects include:
- Itchy skin
- Achy joints
These side effects may go away spontaneously or after switching to another antithyroid medicine.
Important, but rare side effects include:
- Agranulocytosis (a deficiency of white blood cells caused by bone marrow toxicity)—This condition goes away when the medicine is stopped.
- Hepatitis (liver damage)—This is seen more often with propylthiouracil than with methimazole.
Since agranulocytosis is rare and is not predictable by doing blood tests, your doctor must rely on your medical history to determine if this complication may occur. Many doctors obtain a baseline blood count and liver function tests before starting the medicine. If you notice a high fever or serious infection while taking antithyroid medicine, tell your doctor right away. The medicine will need to be stopped if tests show agranulocytosis.
Common names include:
- Propranolol (such as Inderal)
- Atenolol (such as Tenormin)
- Metoprolol (such as Lopressor, Toprol)
Beta-blockers slow the heart rate. They are also helpful for reducing a rapid heartbeat, anxiety, or tremors. These are all symptoms that can occur with hyperthyroidism. Do not stop taking a beta-blocker without checking with your doctor first. If you stop right away, it can cause a dangerous increase in blood pressure.
Possible side effects include:
- Bronchospasm or worsening of asthma or chronic obstructive pulmonary disease (COPD)
- Loss of sex drive
- Difficulty sleeping
Many of these side effects may go away spontaneously as your body gets used to the medicine. Any breathing problems, however, can be serious. Report them to your doctor. Your medicine may need to be stopped or substituted.
If you are taking medicines, follow these general guidelines:
- Take your medicine as directed. Do not change the amount or the schedule.
- Do not stop taking your medicine without talking to your doctor.
- Do not share your medicine.
- Ask what the results and side effects may be. Report them to your doctor.
- Some drugs can be dangerous when mixed with other drugs. Talk to a doctor or pharmacist if you are taking more than one drug. This includes over-the-counter medicine and herb or dietary supplements.
- Plan ahead for refills so you don’t run out.
- Reviewer: Kim Carmichael, MD
- Review Date: 12/2013 -
- Update Date: 01/13/2014 -