The information provided here is meant to give you a general idea about each of the medication 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 medications 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 medications 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 medications 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 medication, 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 medication 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 medication. However, some 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. For this reason, follow-up visits are important.
The main antithyroid medications are the thionamides:
- 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 medications 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 medication your body absorbs into the bloodstream. Therefore, always take your medication 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 medication only needs to be taken once daily. Propylthiouracil is usually taken 3 times a day. This medication 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 medication.
Important, but rare side effects include:
- Neutropenia (a deficiency of white blood cells caused by bone marrow toxicity)—This condition goes away when the medication is stopped.
- Hepatitis (liver damage)—This is seen more often with propylthiouracil than with methimazole.
Since neutropenia 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 medication. If you notice a high fever or serious infection while taking antithyroid medication, tell your doctor right away. The medication will need to be stopped if tests show neutropenia.
Common names include:
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 suddenly, 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 medication. Any breathing problems, however, can be serious. Report them to your doctor. Your medication may need to be stopped or substituted.
If you are taking medications, follow these general guidelines:
- Take your medication as directed. Do not change the amount or schedule.
- Ask what side effects could occur. Report them to your doctor.
- Talk to your doctor before you stop taking any prescription medication.
- Do not share your prescription medication.
- Medications can be dangerous when mixed. Talk to your doctor or pharmacist if you are taking more than one medication, including over-the-counter products and supplements.
- Plan ahead for refills as needed.
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Hyperthyroidism (thyrotoxicosis). Merck Manual Professional Version website. Available at: http://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/thyroid-disorders/hyperthyroidism. Updated July 2016. Accessed November 28, 2017.
Hyperthyroidism and thyrotoxicosis. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T116479/Hyperthyroidism-and-thyrotoxicosis. Updated July 27, 2017. Accessed November 28, 2017.
Primary hyperthyroidism. National Institute of Diabetes and Digestive and Kidney Diseases website. Available at: http://www.niddk.nih.gov/health-information/health-topics/endocrine/primary-hyperparathyroidism/Pages/fact-sheet.aspx. Updated August 2012. Accessed November 28, 2017.
1/30/2009 DynaMed Plus Systematic Literature Surveillancehttp://www.dynamed.com/topics/dmp~AN~T116479/Hyperthyroidism-and-thyrotoxicosis: Nyirenda MJ, Taylor PN, Stoddart M, Beckett GJ, Toft AD. Thyroid-stimulating hormone-receptor antibody and thyroid hormone concentrations in smokers vs nonsmokers with Graves disease treated with carbimazole. JAMA. 2009;301(2):162-164.
Last reviewed November 2018 by EBSCO Medical Review Board James Cornell, MD Last Updated: 12/20/2014