What is hyperthyroidism?
Hyperthyroidism means your thyroid makes too much thyroid hormone. Your thyroid is a gland in the front of your neck. It controls your metabolism, which is how your body turns food into energy. It also affects your heart, muscles, bones, and cholesterol.
Having too much thyroid hormone can make a lot of things in your body speed up. You may lose weight quickly, have a fast heartbeat, sweat a lot, or feel nervous and moody. Or you may have no symptoms at all. While your doctor is doing a test for another reason, he or she may discover that you have hyperthyroidism.
Hyperthyroidism is easily treated. With treatment, you can lead a healthy life. Without treatment, hyperthyroidism can lead to serious heart problems, bone problems, and a dangerous condition called thyroid storm.
What causes hyperthyroidism?
Graves' disease causes most hyperthyroidism. In Graves' disease, the body's natural defence (immune) system attacks the thyroid gland. The thyroid reacts by making too much thyroid hormone. Like many thyroid problems, it often runs in families.
Sometimes hyperthyroidism is caused by a swollen thyroid or small growths in the thyroid called thyroid nodules.
This topic focuses on hyperthyroidism caused by Graves' disease.
What are the symptoms?
You may have no symptoms at all. Or:
- You may feel nervous, moody, weak, or tired.
- Your hands may shake, your heart may beat fast, or you may have problems breathing.
- You may be hot and sweaty or have warm, red, itchy skin.
- You may have more bowel movements than usual.
- You may have fine, soft hair that is falling out.
- You may lose weight even though you eat the same or more than usual.
If you have any of these symptoms, call your doctor. Without treatment, hyperthyroidism can lead to heart problems, bone problems, and a dangerous condition called thyroid storm.
How is hyperthyroidism diagnosed?
Your doctor will ask you about your symptoms and do a physical examination. Then he or she will order blood tests to see how much thyroid hormone your body is making.
Sometimes hyperthyroidism is found while you are having a test for another reason. You may be surprised to find out that you have this problem.
How is it treated?
If your symptoms bother you, your doctor may give you pills called beta-blockers. These can help you feel better while you and your doctor decide what your treatment should be. Hyperthyroidism can lead to more serious problems. So even if your symptoms do not bother you, you still need treatment.
Radioactive iodine and antithyroid medicine are the treatments doctors use most often. The best treatment for you will depend on a number of things, including your age. Some people need more than one kind of treatment.
- Radioactive iodine is the most common treatment. Most people are cured after taking one dose. It destroys part of your thyroid gland, but it does not harm any other parts of your body.
- Antithyroid medicine works best if your symptoms are mild. These pills do not damage your thyroid gland. But they do not always work, and you have to take them at the same time every day. If they stop working, you may need to try radioactive iodine.
After treatment, you will need regular blood tests. These tests check to see if your hyperthyroidism has come back. They also check to see if you are making enough thyroid hormone. Sometimes treatment cures hyperthyroidism but causes the opposite problem—too little thyroid hormone. If this happens, you may need to take thyroid hormone pills for the rest of your life.
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Graves' disease is the most common cause of hyperthyroidism. Graves' disease causes the thyroid gland to make too much thyroid hormone. Graves' disease, like many thyroid problems, often runs in families.
Other common causes include:
- Thyroid nodules. Thyroid nodules are abnormal growths in the thyroid gland that can make too much thyroid hormone. For more information, see the topic Thyroid Nodules.
- Thyroiditis. Thyroiditis occurs when your body makes antibodies that damage your thyroid gland. You can also get thyroiditis from a viral or bacterial infection. At first, thyroiditis may cause your thyroid levels to rise as hormone leaks out from the damaged gland. Later, levels may be low (hypothyroidism) until the gland repairs itself.
Uncommon causes of hyperthyroidism include tumours or eating foods or taking medicines that contain large amounts of iodine.
Hyperthyroidism can occur at any age but rarely affects children. It affects women more often than men.
You may have hyperthyroidism if you:
- Feel nervous, moody, weak, or tired.
- Have hand tremors, or have a fast or irregular heartbeat, or have trouble breathing even when you are resting.
- Feel very hot, sweat a lot, or have warm, red skin that may be itchy.
- Have frequent and sometimes loose bowel movements.
- Have fine, soft hair that is falling out.
- Lose weight even though you are eating normally or more than usual.
Also, some women have irregular menstrual cycles or stop having periods altogether. And some men may develop enlarged breasts.
The symptoms of hyperthyroidism are not the same for everyone. Your symptoms will depend on how much hormone your thyroid gland is making, how long you have had the condition, and your age. If you are older, it's easy to mistakenly dismiss your symptoms as normal signs of aging.
Specific symptoms of Graves' disease
People with Graves' disease often have additional symptoms, including:
- Goiter, which is an enlarged, painless thyroid gland.
- Thickened nails that lift off the nail beds.
- Pretibial myxedema, which is lumpy, reddish, thick skin on the front of the shins and sometimes on top of the feet.
- Clubbing (fingers with wide tips).
- Graves' ophthalmopathy, which causes bulging, reddened eyes, among other symptoms.
Graves' ophthalmopathy is a possible complication of hyperthyroidism. It can occur before, after, or at the same time as your symptoms of hyperthyroidism. People with Graves' ophthalmopathy develop eye problems, including bulging, reddened eyes, sensitivity to light, and blurring or double vision. People who smoke are more likely to develop Graves' ophthalmopathy.
If you have Graves' ophthalmopathy, it may temporarily get worse if you have radioactive iodine treatment. On the other hand, it may get better if you take antithyroid medicine.
If you do not treat your hyperthyroidism, you may:
- Lose weight because your body's metabolism is faster.
- Have heart problems such as rapid heart rate, atrial fibrillation, and heart failure.
- Have trouble replacing calcium and other minerals in your bones, which can lead to osteoporosis.
In rare cases, hyperthyroidism can cause a life-threatening condition called thyroid storm, which happens when the thyroid gland releases large amounts of thyroid hormones in a short period of time.
If your thyroid gland makes too much thyroid hormone, you may have symptoms of hyperthyroidism. Most hyperthyroidism is caused by an immune system problem called Graves' disease. At first, your hyperthyroidism may make you feel hot, have tremors in your hands, or lose weight. Over time, you may notice that your heart is beating fast, that you feel anxious, or that you are having a lot of bowel movements. You may also feel like you just don't have as much energy as usual.
Hyperthyroidism typically does not go away on its own. Most people need treatment to make hyperthyroidism go away. After treatment, many people develop hypothyroidism (too little thyroid hormone).
In rare cases, hyperthyroidism can cause a life-threatening condition called thyroid storm, which occurs when the thyroid gland releases large amounts of thyroid hormones in a short period of time.
What Increases Your Risk
You are more likely to have hyperthyroidism if:
- You are female.
- You have a family history of thyroid problems. People who have close relatives with Graves' disease or other thyroid problems are more likely to develop hyperthyroidism.
- You have an autoimmune disease, such as Addison's disease or type 1 diabetes.
- You smoke cigarettes. People who smoke are more likely to have Graves' disease and are more likely to have Graves' ophthalmopathy.
When should you call your doctor?
The most serious problem associated with hyperthyroidism is a life-threatening condition called thyroid storm.
Call your doctor immediately if you have been diagnosed with hyperthyroidism and:
- You feel very irritable.
- You have unusually high or low blood pressure compared to your normal blood pressure.
- You feel nauseated, are throwing up, or have diarrhea.
- Your heart is beating very fast or you have chest pain.
- You have a fever.
- You are confused or feel sleepy.
- You cannot breathe well or you feel very tired, which can be symptoms of heart failure.
You should also call your doctor if:
- You develop symptoms of Graves' ophthalmopathy, such as bulging, reddened eyes.
- You feel very tired or weak.
- You are losing weight even though you are eating normally or more than usual.
- Your throat is swollen or you are having trouble swallowing.
Watchful waiting is a period of time during which you and your doctor observe your symptoms without using medical treatment. If you think you have symptoms of hyperthyroidism, watchful waiting is not a good idea. Call your doctor if you think you may have hyperthyroidism, so you can be treated early and reduce your chances of having more serious problems.
Who to see
Examinations and Tests
Your doctor will ask questions about your medical history, do a physical examination, and order medical tests to diagnose hyperthyroidism.
If your doctor thinks you may have hyperthyroidism, he or she may order:
- A thyroid-stimulating hormone (TSH) test, which is a blood test that measures your levels of TSH. If your TSH level is low, your doctor will want to do more tests.
- Thyroid hormone tests, which are blood tests to measure your levels of two types of thyroid hormones, called T3 and T4. If your thyroid hormone levels are high, you have hyperthyroidism.
When you are being treated for hyperthyroidism, your doctor will test your TSH and thyroid hormones several times a year to see how well your treatment is working.
After you are diagnosed with hyperthyroidism, your doctor may also want to do:
- An antithyroid antibody test to see if you have the kind of antibodies that attack thyroid tissue. This test can help diagnose Graves' disease and autoimmune thyroiditis.
- A radioactive thyroid scan and radioactive iodine uptake tests, which use radiation and a special camera to find out the cause of your hyperthyroidism.
In Canada, screening is not recommended for people who do not have symptoms of thyroid problems. But testing is recommended for people who have vague symptoms that might be linked to thyroid dysfunction.footnote 1 More frequent testing may be recommended for people who have symptoms of hyperthyroidism or risk factors for the condition, such as:
- Perimenopausal or post-menopausal women.
- People who have a family history of Graves' disease.
- People who have an autoimmune disease such as Addison's disease or type 1 diabetes.
There are three treatments for hyperthyroidism. Antithyroid medicine and radioactive iodine are the ones doctors use most often. In rare cases, surgery may be done. Hyperthyroidism can lead to more serious problems. So even if your symptoms are not bothering you, you still need treatment.
The kind of treatment you have depends on your age, what is causing your hyperthyroidism, how much thyroid hormone your body is making, and other medical conditions you may have. Each kind of treatment has benefits and risks. Discuss the benefits and risks of each kind of treatment with your doctor. For some people, more than one kind of treatment may be needed.
Initial treatment for hyperthyroidism usually is antithyroid medicine or radioactive iodine therapy. If you have a lot of symptoms, your doctor may recommend that you take antithyroid medicine first to help you feel better. Then you can decide whether to have radioactive iodine therapy.
- Antithyroid medicines work best if you have mild hyperthyroidism, if this is the first time you are being treated for Graves' disease, if you are younger than 50, or if your thyroid gland is only swollen a little bit (small goiter).
Radioactive iodine is often recommended if you have Graves' disease and are older than 50, or if you have thyroid nodules (toxic multinodular goiter) that are releasing too much thyroid hormone. Radioactive iodine is not used if:
- You are pregnant or you want to become pregnant within 6 months of treatment.
- You are breastfeeding.
- You have thyroiditis or another kind of hyperthyroidism that is often temporary.
If you have symptoms such as a fast heartbeat, tremors, sweating, nervousness, or dry eyes, you may take some additional medicines to treat those symptoms.
Surgery is not usually part of initial treatment. You may need surgery if your thyroid gland is so big that you have a hard time swallowing or breathing. Or you may need surgery if a single large thyroid nodule is releasing too much thyroid hormone.
During and after treatment for hyperthyroidism, you will have regular blood tests to check your levels of thyroid-stimulating hormone (TSH). You will also have regular thyroid hormone tests to check your levels of hormones called T4 and T3. These tests are a good way to know how well your treatment is working. If your symptoms do not go away after your initial treatment, you may need to repeat the treatment or try a different treatment.
- If you have Graves' disease and have been taking antithyroid medicine but your hyperthyroidism has not improved, you can continue to take antithyroid medicine or you can try radioactive iodine therapy.
- If you have lots of side effects from antithyroid medicines and radioactive iodine is not an option for you, you may need surgery to remove all or part of your thyroid gland (thyroidectomy).
Sometimes treatment cures your hyperthyroidism but may cause hypothyroidism. Hypothyroidism is the opposite of hyperthyroidism—instead of making too much thyroid hormone, your body is now making too little thyroid hormone. Hypothyroidism is most common after treatment with radioactive iodine. But it can also occur after surgery and sometimes after taking antithyroid medicine.
Be sure to call your doctor if you start to gain weight, feel tired, or feel cold more often than usual. These symptoms may mean you have hypothyroidism and you need to take a different medicine called thyroid hormone medicine. For more information, see the topic Hypothyroidism.
Treatment if the condition gets worse
If radioactive iodine or antithyroid medicines are not working well, you may need:
- Another treatment of radioactive iodine.
- Surgery to remove all or part of your thyroid gland (thyroidectomy).
After treatment with radioactive iodine, you may develop hypothyroidism (too little thyroid hormone). Call your doctor if you have any of the symptoms of hypothyroidism such as gaining weight, feeling tired, or feeling cold more often than usual. If you do have hypothyroidism, you may need to take thyroid hormone medicine for the rest of your life. For more information, see the topic Hypothyroidism.
Hyperthyroidism caused by Graves' disease is a genetic disease that you cannot prevent.
People who smoke are more likely to develop Graves' disease and Graves' ophthalmopathy, also called thyroid eye disease, than people who do not smoke.
Be sure to see your doctor regularly so he or she can be sure that your hyperthyroidism treatment is working, that you are taking the right amount of medicine, and that you are not having any side effects.
If you are taking antithyroid medicine, take it at the same time every day.
If you have Graves' ophthalmopathy, you may need to use eyedrops to help moisten your eyes and wear sunglasses to protect your eyes.
To help reduce the symptoms of hyperthyroidism, you can:
- Lower stress. This helps relieve symptoms of anxiety and nervousness.
- Avoid caffeine. Caffeine can make symptoms worse, such as fast heartbeat, nervousness, and difficulty concentrating.
- Quit smoking. If you have Graves' disease and you are a smoker, you are more likely to develop Graves' ophthalmopathy.
Antithyroid medicine is often used for hyperthyroidism, because it works more quickly than radioactive iodine therapy. Radioactive iodine therapy destroys part or all of the thyroid gland, depending on the dosage used. But antithyroid medicine does not cause permanent thyroid damage.
You may take antithyroid medicine before you have radioactive iodine treatment or surgery—to bring your metabolism to normal, to make you feel better, or to reduce the chances of more serious problems.
Antithyroid medicine does control hyperthyroidism in many people. But the medicine does have some drawbacks.
- You have to take the medicine for at least 1 year.
- Your symptoms may come back after you stop taking it. And then you have to start taking antithyroid medicine again or try a different treatment.
- There are some rare side effects from the medicine, ranging from a rash to a low white blood cell count, which can make it hard for your body to fight infection.
Your doctor may prescribe additional medicines to treat symptoms caused by hyperthyroidism, such as rapid heartbeat or dry eyes. These medicines can help you feel better while you wait for another treatment to begin to work.
What to think about
- Antithyroid medicine may or may not make your hyperthyroidism permanently go away. The medicine is much more effective in people with mild disease. About 30 out of 100 people will have their hyperthyroidism go away (go into remission) after taking antithyroid medicine for 12 to 18 months.footnote 2
- Antithyroid medicine works best if you have mild hyperthyroidism, if this is the first time you are being treated for Graves' disease, if you are younger than 50, or if your thyroid gland is only swollen a little bit (small goiter). It is not used for thyroiditis.
- Antithyroid medicine is used instead of radioactive iodine if you are pregnant, breastfeeding, or trying to become pregnant.
- Children are treated with antithyroid medicine, because experts do not know if radioactive iodine treatment is safe for children. Treating children with antithyroid medicine is challenging. It is hard to know how much medicine they need when they are growing so quickly.
- Your doctor may prescribe low doses of thyroid hormone medicine to take with your antithyroid medicine so that your thyroid hormone levels do not get too low.
Surgery for hyperthyroidism (thyroidectomy) removes part or all of the thyroid gland. Doctors rarely use this surgery to treat hyperthyroidism. You may need surgery if:
- Your thyroid gland is so big that it is hard for you to swallow or breathe.
- You have thyroid cancer or your doctor suspects you have thyroid cancer. For more information, see the topic Thyroid Cancer.
- You had serious side effects from taking antithyroid medicines. And radioactive iodine is not an option for you.
- You have a large goiter that radioactive iodine treatment did not shrink.
- You have a single, large thyroid nodule that is making too much thyroid hormone, and radioactive iodine did not effectively treat the nodule.
What to think about
If you are having surgery, your doctor will have you take antithyroid medicines before surgery to bring your thyroid hormone levels as close to normal as possible.
After surgery, your doctor will check your thyroid hormone levels regularly, because you may develop hypothyroidism (too little thyroid hormone). Hypothyroidism is treated with thyroid hormone medicine. For more information, see the topic Hypothyroidism.
Surgery is the fastest way to treat your hyperthyroidism. But it is not used very often and is more risky than other treatments.
Radioactive iodine is considered by many doctors to be the best treatment for hyperthyroidism. You swallow it in a liquid form or capsule, and the iodine is taken up by your thyroid gland. The radioactivity in the iodine kills most or all of the tissue in your thyroid gland. But it does not harm any other parts of your body.
What to think about
Most people are cured of hyperthyroidism after one dose of radioactive iodine.
The main drawback of radioactive iodine is that it can damage your thyroid gland so that your body no longer produces enough thyroid hormone. This is a common result of treatment. And most people who receive radioactive iodine eventually develop hypothyroidism (having too little thyroid hormone). If you develop hypothyroidism, you will need to take thyroid hormone medicine for the rest of your life. For more information, see the topic Hypothyroidism.
Radioactive iodine should not be used by children or by women who are pregnant, women who are breastfeeding, or women who want to become pregnant within 6 months of treatment.
Doctors have used radioactive iodine to treat hyperthyroidism for more than 60 years. There is no evidence that radioactive iodine causes cancer, infertility, or birth defects.
- Beaulieu M-D (1994). Screening for thyroid disorders and thyroid cancer in asymptomatic adults. In Canadian Task Force on the Periodic Health Examination, Canadian Guide to Clinical Preventive Health Care, pp. 611–618. Ottawa: Health Canada. Also available online: http://www.phac-aspc.gc.ca/publicat/clinic-clinique/pdf/s7c51e.pdf.
- Jameson JL, et al. (2015). Disorders of the thyroid gland. In DL Kasper et al., eds., Harrison's Principles of Internal Medicine, 19th ed., vol. 2, pp. 2283–2308. New York: McGraw-Hill Education.
Other Works Consulted
- Bahn RS, et al. (2011). Hyperthyroidism and other causes of thyrotoxicosis: Management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Thyroid, 21(6): 593–646. Also available online: http://www.liebertonline.com/doi/full/10.1089/thy.2010.0417.
- Hueston WJ (2011). Hyperthyroidism. In ET Bope et al., eds., Conn's Current Therapy 2011, pp. 681–683. Philadelphia: Saunders.
- Mandel SJ, et al. (2011). Thyrotoxicosis. In S Melmed et al., eds., Williams Textbook of Endocrinology, 12th ed., pp. 362–405. Philadelphia: Saunders.
- Nygaard B (2014). Hyperthyroidism (primary). BMJ Clinical Evidence. http://clinicalevidence.bmj.com/x/systematic-review/0605/overview.html. Accessed April 14, 2016.
Current as of: July 29, 2019
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Anne C. Poinier MD - Internal Medicine
Adam Husney MD - Family Medicine
Kathleen Romito MD - Family Medicine
David C.W. Lau MD, PhD, FRCPC - Endocrinology
Current as of: July 29, 2019