Click here for Frequently Asked Questions on Hyperthyroidism.

Excess circulating thyroid hormone denotes the presence of Hyperthyroidism. The symptoms of hyperthyroidism vary from patient to patient, and may include one or more of the following:

None of the above symptoms, alone or together in various combinations, are diagnostic of hyperthyroidism. Indeed, many of these symptoms may occasionally be noted, at times, in otherwise healthy individuals who do not have thyroid disease. Similarly patients may have biochemical evidence for hyperthyroidism with abnormal thyroid function tests and yet may not be experiencing the majority, or in fact any of the above symptoms. Notably, older subjects with hyperthyroidism often present with fewer of the classical symptoms, whereas smokers may present with more symptoms Older Subjects with Hyperthyroidism Present with a Paucity of Symptoms and Signs: A Large Cross-Sectional Study J Clin Endocrinol Metab. 2010 Apr 14. [Epub ahead of print].

There is significant variability in the individual response to hyperthyroidism. The actual symptoms experienced by individuals may range from few to none, in the case of mild hyperthyroidism. Alternatively, patients with more severe hyperthyroidism may be quite unwell and have many of the above symptoms.


A diagnosis of Hyperthyroidism is suggested by the presence of appropriate symptoms, and may be made more precisely once a history, physical examination, and laboratory investigations have been carried out. Initial investigations usually include blood tests to assess the levels of circulating TSH and thyroid hormones (T4 and T3, often Free T4 and Free T3). Given the sensitivity of the pituitary gland to correct levels of circulating thyroid hormones, the TSH is usually decreased or undetectable if primary hyperthyroidism is present. In many medical practices and laboratories, the TSH is often the initial screening test done if thyroid disease is suspected. If the TSH is normal, and pituitary disease is not suspected, no further investigations may be indicated.

There are several conditions that may produce Hyperthyroidism, including:


In addition to blood work, investigations may include an iodine uptake test to determine how much iodine the thyroid gland is capable of taking up. This allows detection of conditions where the thyroid gland is working too hard (Graves' disease, single hot nodules or multiple hyperfunctioning nodules), and hence the iodine uptake is usually elevated. Pregnant or breast feeding women should not have scans or any tests involving radiation exposure.

If the iodine uptake is very low in the presence of hyperthyroidism, this often implies the presence of inflammation or suppression of iodine uptake by excess iodine or exogenous drugs or ingestion of thyroid hormone. Patients with hyperthyroidism and multinodular goiters may have normal to increased iodine uptake. Similarly, patients with very mild Graves' disease (GD) may have a normal iodine uptake, although most patients with GD will have an elevated iodine uptake. Conversely, patients in the recovery phase of thyroiditis may also exhibit an elevated radioactive iodine uptake. Hence the iodine uptake needs to be interpreted in the appropriate clinical context.

Occasionally, a thyroid scan may also be done to discern the region(s) of the thyroid gland that actually take up the radioisotope. Scans are done with radioactive isotopes such as technetium or iodine that are given in small amounts, result in minimal radiation exposure, and are safe with no known side effects.

Ultrasound examinations are generally not required for the investigation of hyperthyroidism, unless assessment of the extent of nodular thyroid disease is being carried out independently.


The 3 principal treatment options for Hyperthyroidism are Medications, Radioactive iodine or Surgery.

Selection of the appropriate treatment option may be influenced by the type of hyperthyroidism present, clinical severity of the disease, co-existing medical conditions and drugs, current or planned pregnancy, and importantly, patient preference. Treatment options, including the pros and cons of each treatment type, should be carefully considered. For a summary of consensus management guidelines for different types of hyperthyroidism, see Hyperthyroidism and Other Causes of Thyrotoxicosis: Management Guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists Thyroid. 2011 Apr 21

Medications (drugs) may be taken to block release of thyroid hormone from the gland (iodine), or to block some of the systemic effects of thyroid hormone and coexistent sympathetic nervous system over-activity (ß blockers such as propranolol, metoprolol, atenololol, and others). The principal drugs that decrease the synthesis of thyroid hormone are propylthiouracil (PTU) and methimazole used in North America and carbimazole used in Europe and Asia.

Medications may be used initially in all cases of severe hyperthyroidism irrespective of the etiology, but most commonly, represent a long term definitive treatment option principally for patients with Graves' Disease. Patients with Graves' Disease may be treated with antithyroid drugs for periods of time ranging from 6 months to 2 years. Patients should be aware of and remain alert for the potential side effects of these ‘antithyroid’ medications such as PTU and methimazole. Carbimazole, a related medication, is not widely used in North America. For more information, see Medications for treatment of hyperthyroidism.

Radioactive iodine works by destroying the thyroid cells that are hyperfunctioning and hence these overactive thyroid cells are more likely than normal thyroid cells to take up excess exogenously administered iodine. The rationale for this treatment is based on the observation that normal thyroid cells take up iodine in the process of making thyroid hormone (which contains iodine). It is generally not realistic to expect that a precise amount of radioactive iodine can be given that will restore thyroid function to normal, without incurring a significant risk of hypothyroidism or inadequate treatment. Accordingly, the principal and expected complication or side effect associated with radioactive iodine for the treatment of GD is the development of hypothyroidism requiring life long thyroid hormone replacement. Radioactive iodine should not be given to pregnant patients. Patients considering pregnancy within 6-12 months of receiving  radioactive iodine should discuss optimal treatment plans carefully with their physician.

Surgery removes part (in the case of hyperfunctioning nodules) or nearly all (in the case of a multinodular or Graves' Disease gland) of the thyroid gland responsible for the development of hyperthyroidism. The complications of surgery may include damage to local structures such as the recurrent laryngeal nerves, or the development of a low calcium level (hypocalcemia) if significant amounts of parathyroid tissue are removed or damaged. The risks of developing specific complications depends on various factors including the extent and type of surgery to be carried out, local anatomy, a history of previous thyroid operations, co-existing medical conditions, and the skill of the thyroid surgeon.

Review Guidelines for the diagnosis and treatment of hyperthyroidism and hypothyroidism prepared in 2002 by the American Association of Clinical Endocrinologists.


I have been told that the radioactive iodine treatment is safe but I am scared and I heard that you can get cancer many years later. How safe is this treatment?

Radioactive iodine has been used for the treatment of hyperthyroidism for over 50 years. Several studies have examined cancer mortality in long term follow-up of patients treated with radioactive iodine. In many of the studies, there does not appear to be any significant excess total cancer mortality in patients after radioactive iodine. For example, see the study published in JAMA 1998 280:347-355 or in Lancet 1999 353:2111-2115.   However, other studies show a slightly increased risk of some forms of cancer after many years   Association of Radioactive Iodine Treatment With Cancer Mortality in Patients With Hyperthyroidism JAMA Intern Med. 2019 Jul 1. doi: 10.1001/jamainternmed.2019.0981

Are there any factors that are useful for predicting my response to treatment if I have Graves' disease?

Patients with severe hyperthyroidism and large thyroid glands have lower rates of remission with antithyroid medications. It appears that male patients, and patients less than 40 years of age are more likely to exhibit a lower remission rate and/or to require higher does of radioactive iodine. For an overview, see J Clin Endocrinol Metab 2000 Mar;85(3):1038-42 Age and gender predict the outcome of treatment for Graves' hyperthyroidism.

I received my radioactive iodine 2 weeks ago, and now all my symptoms are worse! What is going on?

Radioactive iodine will induce an inflammation in the thyroid gland as part of the process by which thyroid cells are destroyed. The inflammation will cause thyroid cells to become leaky and thyroid hormone will escape into the blood, resulting in higher levels of circulating thyroid hormones for several weeks. Accordingly, in some patients, the symptoms of hyperthyroidism may become more prominent for several weeks after radioactive iodine administration. This problem is usually transient and lasts for only a few days or weeks, and if necessary, symptoms can be treated in part through use of beta blockers, where appropriate. In some patients, moderate to severe neck tenderness develops as a result of the inflammation and these symptoms, as well as the transient hyperthyroidism, can actually persist for 1-2 months after radioactive iodine.

My blood tests indicate that I have been hyperthyroid for 6 months but I feel fine. Do I need treatment?

Mild hyperthyroidism is often well tolerated, especially in younger individuals. Nevertheless, over longer periods of time, there may be harmful effects on bone mass (osteoporosis), and the heart (rapid or irregular heat beats and thickening of the heart muscle). Menstrual periods and ovulation may also become irregular, and muscle weakness may develop. In older patients, even mild hyperthyroidism may predispose patients to the sudden development of  rapid irregular heartbeats, which can be dangerous. However, even in younger patients with mild hyperthyroidism who "feel fine" a more careful evaluation may reveal mild symptoms attributable to hyperthyroidism, and evidence that the hyperthyroidism may be adversely affecting the heart. For example, see Endogenous Subclinical Hyperthyroidism Affects Quality of Life and Cardiac Morphology and Function in Young and Middle-Aged Patients. J Clin Endocrinol Metab. 2000 Dec;85(12):4701-4705. Hence it is appropriate to discuss these issues with your physician when considering the treatment of mild, "subclinical" or asymptomatic hyperthyroidism. To review the opinion of thyroid experts deduced from a set of survey  questions, see The management of subclinical hyperthyroidism by thyroid specialists. Thyroid. 2003 Dec;13(12): 1133-9.  

Many older patients will have normal levels or borderline high levels of thyroid hormones, a low TSH, and have "subclinical hyperthyroidism". Indeed, many of the classical symptoms of hyperthyroidism are less frequent or can be absent in older subjects with hyperthyroidism Older subjects with hyperthyroidism present with a paucity of symptoms and signs: a large cross-sectional studyJ Clin Endocrinol Metab. 2010 Jun;95(6):2715-26

A dilemma is whether or not to treat these asymptomatic patients as a low but defined percent of subjects may progress to develop more severe hyperthyroidism, or rapid or irregualr heart beats (atrial fibrillation). Although probably 90% of subjects in this category may be fine without treatment, each case is special and warrants and evaluation of the risks and benefits of treatment. See Natural history of subclinical hyperthyroidism in elderly patients with TSH between 0.1 and 0.4 mIU/L: a prospective study. Clin Endocrinol (Oxf). 2009 Sep 10. [Epub ahead of print]. Similarly, the majority of subjects with mild biochemical subclinical hyperthyroidism did not progress to more severe overt hyperthyroidism in follow-up ranging from 12-70 months Natural history of subclinical hyperthyroidism in elderly patients with TSH between 0.1 and 0.4 mIU/l: a prospective studyClin Endocrinol (Oxf). 2010 May;72(5):685-8.  While some physicians will advocate treatment of subclinical hyperthyroidism to prevent the development of complications, other physicians will recommend a watchful waiting scenario. Should we treat mild subclinical/mild hyperthyroidism? No.

Eur J Intern Med. 2011 Aug;22(4):330-3. Evaluation of heart rate responses after exercise reveals slightly increased heart rates that do not return as quickly to normal after recovery in subjects with sublinical hyperthyroidism Differences in Heart Rate Profile during Exercise among Subjects with Subclinical Thyroid Disease Thyroid. 2013 Jun 18

For more information, see Heart Disease.

I am losing my hair and I find this quite distressing. Is this related to my thyroid condition and will my hair grow back?

Hair loss is not uncommon when thyroid hormone levels are changing. Hair loss can occur during persistent hyperthyroidism, or when thyroid hormone levels are falling or rising. In the vast majority of cases, hair loss related to changes in levels of thyroid hormones is transient, and reversible. Nevertheless, as hair growth is extremely slow, and hair loss may continue for several months after a thyroid problem is corrected, it may take many months to a year or so before hair regrowth becomes evident. If hair loss persists even after correction of the thyroid problem, causes of hair loss other than thyroid disease should be considered

I have been told that everyone with hyperthyroidism loses weight but I have gained weight! What is going on?

Although many patients with hyperthyroidism will indeed lose weight, weight gain is not uncommon. Hyperthyroidism will also result in an increased appetite, and in some patients, an increased appetite and increased food intake may lead to weight gain, despite an increase in metabolic rate that usually accompanies hyperthyroidism.

My friend was treated for hyperthyroidism with radioactive iodine and gained 30 lbs! Will this happen to me?

Optimal treatment for hyperthyroidism involves restoration of normal thyroid function. The vast majority of patients, if monitored carefully, will not become extremely hypothyroid and should not experience tremendous weight gain. Nevertheless, some degree of weight gain is a clearly documented fact in patients with hyperthyroidism who are treated successfully, with patients who were previously heavy, or who had lost considerable weight as a result of the hyperthyroid state, or who become hypothyroid as a result of treatment, gaining more weight. See Weight gain following treatment of hyperthyroidism. Clin Endocrinol (Oxf). 2001 55(2):233-9. and Early treatment of incipient hypothyroidism with thyroxine, and regular compliance, may help reduce the weight gain. Weight gain in patients after therapy for hyperthyroidism. S Afr Med J. 2003 Jul;93(7):529-31.

Patients who have had hyperthyroidism for months to years may become used to eating whatever they wish with no concern for weight gain due to the increase in metabolic rate associated with hyperthyroidism. When hyperthyroidism is rapidly corrected, if food intake is not reduced to the previously 'normal' state, such patients may experience weight gain if food intake remains "abnormally" high once the hyperthyroidism is corrected. Patients concerned about weight gain should pay careful attention to their food intake as the hyperthyroidism is being treated. Patients should also should discuss with their physician the optimal regimen for monitoring their thyroid status during correction of hyperthyroidism, as well as recommendations for physical activity/exercise once their hyperthyroidism is adequately controlled. Aggressive monitoring of thyroid status and early institution of thyroid hormone replacement at doses aimed at ultimately keeping the TSH at the lower limit of normal may help prevent excessive weight gain during the treatment of hyperthyroidism.

I received radioactive iodine 10 years ago and now I have hyperthyroidism again! How is this possible?

Radioactive iodine, when given in sufficient doses, will generally destroy enough functioning thyroid tissue to render patients hypothyroid or euthyroid (normal thyroid function). Nevertheless, it is possible that a resistant group of thyroid cells that was not originally damaged by the radioactive iodine treatment can gradually increase in number and function over many years so that clinical hyperthyroidism can return many years or even decades later.

I am scheduled for an outpatient radioactive iodine treatment. What is the risk of radiation exposure to my family?

At the dosing limits allowed for prescribing outpatient use of radioactive iodine, there appears to be little risk to family members in the home environment. Patients are encouraged to minimize immediate close contact for a few days, especially of body fluids such as saliva and other excretions. For example, avoid intimate kissing, sharing of food, and hugging and kissing of young children for a few days after the radioactive iodine treatment. A scientific study of this issue is reported in Radiation exposure from outpatient radioactive iodine (131I) therapy for thyroid carcinoma. JAMA. 2000 May 3; 283 (17) :2272-4.

I have hyperthyroidism and I feel very sick. Do I have thyroid storm?

Thyroid storm is generally defined as "end organ failure" in response to severe hyperthyroidism. For example, patients who have a rapid heart rate, muscle weakness and fatigue, may have severe hyperthyroidism. Patients with a high fever, a rapid irregular heart rate causing congestive heart failure, and neurological impairment with confusion, may have "thyroid storm". This is a clinical diagnosis, usually associated with other pre-existing medical conditions that aggravate the hyperthyroidism, such as infection. If you think you may be experiencing thyroid storm, contact your physician immediately or go to a hospital emergency room

Is hyperthyroidism treated differently in children?

The 3 treatment options, medications, surgery, and radioactive iodine, are still equally valid for treatment of hyperthyroidism in children. Although for many years, many pediatric endocrinologists have not chosen radioactive iodine as an initial treatment of choice, treatment trends and preferences now seem to be changing, with more use of radioactive iodine and surgery in some centers. For an overview, see Graves' disease in childhood. J Pediatr Endocrinol Metab. 2001 Mar;14(3):229-43 and Graves disease in childhood: a review of the options for diagnosis and treatment. Paediatr Drugs. 2003;5(2):95-102.

I am having difficulty concentrating and I am increasingly forgetful. Is this all related to my hyperthyroidism?

Patients with severe hyperthyroidism can have very mild difficulty with cognitive function, concentration, and memory, which should resolve or improve with treatment of disease. A more severe impairment in mental function, or problems that persist following correction of the hyperthyroidism, should prompt investigation for other causes of the problem, aside from the hyperthyroidism. Nevertheless, in very rare instances, a reversible type of "hyperthyroid dementia" has been reported, as described in Hyperthyroid dementia: clinicoradiological findings and response to treatment. J Neurol Sci. 2001 Feb 15;184(1):81-8.

I have hyperthyroidism, thickening of the skin over my shins and I have been told this is called "pretibial myxedema" and is related to my Graves' Disease. Will this go away when my thyroid is treated?

This skin condition can be a frustrating disease to treat. Although some patients respond to treatment with topical steroids, others do not. In about half the cases, the skin problem may persist for many years. For an overview of treatment outcomes and the natural history of this condition see Dermopathy of Graves' disease (pretibial myxedema): long-term outcome. J Clin Endocrinol Metab. 2002 Feb;87(2):438-46.

I am hyperthyroid and my thyroid gland is enlarged. Should I be worried about thyroid cancer?

Co-existence of hyperthyroidism and thyroid cancer is rare, likely less than 2 % of all cases. Suspicion should be higher if there is a single cold nodule within an otherwise hyperfunctioning thyroid gland. See Thyroid cancer in patients with hyperthyroidism. Horm Res. 2003;60(2):79-83.

My TSH test is never normal, yet my doctor is a bit vague as to whether I should take thyroid hormone?

In many patients, the TSH may be slightly low (mild hyperthyroidism) or slightly high (mild hypothyroidism), and the patient may or may not have symptoms attributable to the modest change in levels of thyroid hormones. In such cases, it is important to review the general health of each patient, the size of the thyroid gland, the presence or absence of heart disease, osteoporosis, and related medical problems, and the potential risks and benefits of "treating" the abnormal lab value and rendering the TSH normal. Considerations include the ongoing and future risks of osteoporosis, heart disease, and related issues. For an overview of the clinical approach to treating "subclinical" disturbances of thyroid hormones, see Approach to the patient with subclinical hyperthyroidism. J Clin Endocrinol Metab. 2007 Jan;92(1):3-9 and  Subclinical thyroid disease: clinical applications. JAMA. 2004 Jan 14; 291(2): 239-43 and Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA. 2004 Jan 14; 291(2): 228-38. Review. and Natural history of subclinical hyperthyroidism in elderly patients with TSH between 0.1 and 0.4 mIU/l: a prospective studyClin Endocrinol (Oxf). 2010 May;72(5):685-8