Click here for Frequently Asked Questions on Hypothyroidism.

Insufficient levels of circulating thyroid hormones is the biochemical hallmark of an under active thyroid, a condition referred to as Hypothyroidism. Symptoms of Hypothyroidism may be varied, and can include: 

In mild forms of hypothyroidism, patients may feel completely well, and have no symptoms. More severe and persistent hypothyroidism may lead to the development of one or more of the above symptoms. It is important to remember that all of the above symptoms are quite non-specific, and the presence of one or more of these complaints by no means implies the presence of hypothyroidism. One can have multiple symptoms and have normal levels of circulating thyroid hormones, or conversely, one can have significant biochemical hypothyroidism in the absence of symptoms. Some patients with hypothyroidism may experience weight gain, due to a combination of factors that include fluid retention, a reduced ability to burn calories, and increased levels of hormones that drive hunger Serum ghrelin levels are increased in hypothyroid patients and become normalized by L-thyroxin treatment J Clin Endocrinol Metab. 2008 Apr 1; [Epub ahead of print].

The Causes of hypothyroidism may include:

Diagnosis of Hypothyroidism

In most settings, a TSH blood test is the initial screening test ordered to make the diagnosis of primary hypothyroidism. The hypothalamus and pituitary are highly sensitive to the appropriate circulating concentrations of thyroid hormones. Furthermore, the pituitary gland constantly converts thyroxine (T4) to T3, providing a sensitive mechanism for readout of thyroid hormone status. When the hypothalamus and pituitary sense that the levels of thyroid hormones are even just slightly subnormal, signals are initiated that increase the secretion of TSH from the pituitary gland. 

TSH is easily and accurately measured using very reliable blood tests, and is currently the best test for detection of primary hypothyroidism (primary hypothyroidism indicates the thyroid is not working). It is important to remember that the TSH test may not be reliable if the hypothalamus or pituitary are damaged. For example, patients with known or suspected pituitary disease may have secondary hypothyroidism (the thyroid is fine, but secondary control mechanisms in the brain are impaired) and require additional testing to accurately determine thyroid status. Some patients have a remote history of surgery, meningitis, trauma, or radiation to the brain that may have involved the hypothalamus or pituitary, perhaps for treatment of cancer. In these patients, levels of thyroxine and TSH alone may not be sufficient for 100% accurate diagnosis of hypothyroidism, and additional dynamic testing, such as a TRH test, may be indicated. For example, see J Clin Endocrinol Metab 1999 Dec;84(12):4472-9 Diagnosis of hidden central hypothyroidism in survivors of childhood cancer.

The TSH can vary across a normal range, and occasionally patients with a high normal TSH may feel slightly hypothyroid and may benefit from treatment that achieves a low normal TSH, but this situation in uncommon. The signs and symptoms of hypothyroidism can be subtle, or non-specific, and the condition can be difficult to diagnose, as illustrated in Accuracy of physical examination in the diagnosis of hypothyroidism: a cross-sectional, double-blind study. J Postgrad Med. 2004 Jan-Mar;50(1):7-10.

Moreover, there is some evidence that "normal" TSH levels may vary with age, as older individuals may have somewhat higher levels of TSH, yet still have no evidence of thyroid dysfunction, as outlined in Age-Specific Distribution of Serum TSH and Antithyroid Antibodies in the United States Population; Implications for the Prevalence of Subclinical Hypothyroidism. J Clin Endocrinol Metab. 2007 Oct 2; [Epub ahead of print]

Treatment of Hypothyroidism

If hypothyroidism is persistent and is associated with one or more troubling symptoms, treatment may be indicated. To review the diagnosis, and management of hypothyroidism, see Clinical Practice Guidelines for Hypothyroidism in Adults: Co-sponsored by American Association of Clinical Endocrinologists and the American Thyroid Association Endocr Pract. 2012 Sep 11:1-207. For an overview of considerations related to thyroid hormone replacement, see Treatment With Thyroid Hormone. Endocr Rev. 2014 Jan 16:er20131083.


Alternatively, if significant enlargement of the thyroid (goiter) is occurring because thyroid function is not adequate and TSH is elevated, treatment may also be considered. Similarly, if pregnancy is contemplated, treatment for hypothyroidism should be initiated. Other patients may have elevated levels of cholesterol that may be aggravated somewhat by an elevated TSH.

Treatment is usually initiated by starting patients on a small dose of L-thyroxine (T4). The medication thyroxine is identical to the T4 or thyroxine normally produced by our own thyroid, hence side effects range from minimal to none, as long as the correct dose of thyroxine is eventually prescribed. The starting dose of thyroxine usually ranges from 0.025 to 0.05 mg a day, and may be higher in younger otherwise healthy individuals. In older patients, or patients with co-existing or suspected heart disease, it is especially important to start with a low dose of thyroid hormone, so as not to aggravate concurrent or unsuspected conditions such as angina or other forms of heart disease. See Thyroid disease and the heart. Indeed, having too much T3 can be an independent risk factor for development of heart disease, as seen in Excess triiodothyronine as a risk factor of coronary events Arch Intern Med 2000 10;160(13):1993-9.

There remains some controversy in the literature and in clinical practice about the merits of replacing both T3 and T4 versus T4 alone. At present, there are a few randomized controlled clinical studies that have examined this issue in large numbers of patients. For an overview of this topic, see a discussion on controversies Optimal Thyroid Hormone Replacement.

To determine if the levels of thyroid hormone have been corrected, a repeat set of blood tests, usually a TSH and perhaps a Free T4 or Free T3, should be obtained after about 4 weeks following initiation of treatment. As thyroid hormone has a long half life, it takes 3-4 weeks for a new steady state level of thyroid hormone to equilibrate in the blood. Hence retesting too early after initiation of thyroxine may give inaccurate results.

Many patients taking thyroid hormone are concerned about the possibility of osteoporosis. The individual risk factors for osteoporosis in each patient should be reviewed with your physician. Nevertheless, many patients with normal levels of thyroid hormone are concerned about osteoporosis and their thyroid status, and these concerns may often be alleviated by briefly reviewing the evidence linking thyroid disease and osteoporosis. Simply put, in patients taking thyroxine who have normal levels of TSH, there is no evidence linking physiological thyroid hormone replacement with an increased risk of osteoporosis.

Hypothyroidism and Your Heart

Although treatment of hypothyroid patients who have heart disease may increase energy and cardiac function, treatment must be initiated slowly, and low doses of thyroid hormone should be used. Many patients with significant degrees of hypothyroidism may have a reduced heart rate, and occasionally reduced function of the heart due to the  lack of the beneficial action of thyroid hormone on the heart muscle. Treatment of patients with thyroid hormone will usually gradually improve the normal function of the heart muscle, however caution is indicated in such instances. As even small amounts of thyroid hormone can speed up the metabolic activity and oxygen consumption of your heart, this may cause angina or palpitations and rapid heart beats in some susceptible patients. Accordingly, even though it may take longer to build up to normal levels of thyroid hormone, it is best to be cautious about replacing thyroid hormone in hypothyroid patients with heart disease. For more information, see Heart disease.

Are there benefits to treating asymptomatic subclinical hypothyroidism in patients with heart disease, especially in the setting of coronary artery disease?

This is a controversial area, and it is likely that treatment decisions will be greatly influenced by individual patient circumstances. A cross sectional study of older individuals screened for hypothyroidism and then followed for several years assessed disability in daily life, depressive symptoms, cognitive function, and mortality from age 85 years through 89 years. There was no correlation between an elevated TSH and problems of this type, and indeed, an elevated TSH seemed to be associated with a prolonged life span. See Thyroid status, disability and cognitive function, and survival in old age. JAMA. 2004 Dec 1;292(21) :2591-9.

Patients with modest elevations in TSH who also have high cholesterol levels and increased risk of heart disease may also experience some benefit from correction of the hypothyroid state, principally a modest but significant reduction in the levels of LDL cholesterol. See Lipoprotein profile in subclinical hypothyroidism: response to levothyroxine replacement, a randomized placebo-controlled study. J Clin Endocrinol Metab. 2002 Apr;87(4):1533-8. Similarly, female patients with a slight TSH elevation with no other symptoms, often referred to as subclinical hypothyroidism, appear to have a modest excess of cardiac risk factors, including increased blood pressure and cholesterol as shown in a small study Risk factors for cardiovascular disease in women with subclinical hypothyroidism. Thyroid. 2002 May;12(5):421-5.

For an overview of the cardiac abnormalities that may be present in patients with mild hypothyroidism, see Cardiovascular and atherogenic aspects of subclinical hypothyroidism Thyroid 2000 Aug;10(8):665-79 and Effects of subclinical thyroid dysfunction on the heart. Ann Intern Med. 2002 Dec 3;137(11):904-14. Review.

Patients with a history of hypothyroidism, especially those taking thyroxine, should have their TSH monitored prior to and several times during pregnancy, perhaps every 8-12 weeks, or more frequently depending on the pattern of weight gain, to ensure that the TSH and levels of free thyroid hormones remain in the normal range throughout pregnancy.  For more information, see Pregnancy.

Review Guidelines for the diagnosis and treatment of hyperthyroidism and hypothyroidism prepared in 2002 by the American Association of Clinical Endocrinologists. For an overview of hypothyroidism, see Hypothyroidism. Lancet. 2004 Mar 6;363(9411):793-803.


My doctor says my TSH is now normal, but I still feel tired and have many of my original symptoms. Can the test be wrong?

The thyroid hormone and TSH tests are generally quite accurate and give a correct reading of the levels of thyroid hormone in your blood. Nevertheless, it can take several weeks to months for your body to realize the full benefit of having normal levels of thyroid hormone again after initiating thyroid hormone therapy, even after the TSH becomes normal. If after several months of normal thyroid hormone levels, several symptoms and complaints persist, they are not likely to be related to the previous state of hypothyroidism and these symptoms should be reviewed with your health care provider. It is also important to remember that the symptoms are very non-specific and may not have been related to the modest degree of hypothyroidism. Indeed, many patients with "classic symptoms of hypothyroidism" are disappointed when informed that their tests are normal and show no evidence for thyroid abnormalities. A fringe element of health practioners claims current blood tests are inaccurate and use ancillary measures including hair analyses and body temperature as measures of thyroid function. To determine whether patients with such symptoms yet normal thyroid blood tests might benefit from thyroid hormone replacement, Pollock and colleagues administered 100 ug of thyroxine or placebo to 25 patients for 6 weeks in a crossover randomized trial. Study measurements included a battery of measures that assessed cognitive function and psychological and physical wellbeing. The results of the study clearly showed no significant improvement in these endpoints, despite higher levels of circulating thyroid hormones in the thyroxine treated patients. To review the data, see Thyroxine treatment in patients with symptoms of hypothyroidism but thyroid function tests within the reference range: randomised double blind placebo controlled crossover trial. BMJ. 2001 Oct 20;323(7318):891-5.

A mild degree of hypothyroidism is not uncommon in patients screened with thyroid blood tests, and "subclinical hypothyroidism" is generally defined as the presence of a normal Free T4, slightly elevated TSH, and the questionable presence or absence of symptoms that may not be related to thyroid function. The treatment of subclinical hypothyroidism remains controversial, with some experts advocating that all such patients should be treated with thyroxine, whereas other thyroid experts advocate a more individualized approach. A  small randomized study in 40 women examined metabolic parameters and psychological function in women treated with thyroid hormone or placebo for six months. No significant clinical benefit could be observed in the thyroxine-treated subjects. See A 6-month randomized trial of thyroxine treatment in women with mild subclinical hypothyroidism. Am J Med. 2002 Apr 1;112(5):348-54.

In contrast, other studies have shown a correlation between increased levels of TSH and mild cognitive impairment Serum thyroxine level and cognitive decline in euthyroid older women. Neurology. 2002 Apr 9;58(7):1055-1061. This is a controversial area, with some physicians advocating treatment, whereas others are not so sure. See Subclinical hypothyroidism: the case against treatment. Trends Endocrinol Metab. 2003 Aug;14(6):262-6.

I have had several persistently elevated TSH levels but I feel fine, and I don't want to take thyroid hormone. What are the options?

Analysis of changes in TSH levels in individuals 65 and over with "subclinical hypothyroidism" have shown that TSH levels remain stable or in the same range in the majority of subjects for several years. A substantial proportion of individuals with mild TSH elevations 4.5–6.9, aw their TSH return to normal. Individuals with TSH levels of 10 or more more commonly progressed to development of clinically evident hypothyroidism with further increases in TSH The Natural History of Subclinical Hypothyroidism in the Elderly: The Cardiovascular Health Study J Clin Endocrinol Metab 2012 97: 1962-1969; doi:10.1210/jc.2011-3047

Patients who feel well but have biochemical evidence for hypothyroidism are classified as having subclinical hypothyroidism (see above). Many of these patients, especially those with positive thyroid antibodies, will later go on to develop symptomatic hypothyroidism and ultimately end up on thyroid hormone. Nevertheless, if the thyroid gland is normal in size, and the patient feels well, another reasonable option is to continue periodically monitoring the situation, without immediately instituting thyroid hormone therapy. Indeed, some patients will continue to have a modest TSH elevation without further progression to significant hypothyroidism, for many years. See Prospective study of the spontaneous course of subclinical hypothyroidism: prognostic value of thyrotropin, thyroid reserve, and thyroid antibodies. J Clin Endocrinol Metab. 2002 Jul;87(7):3221-6.

Some of my friends take T3 and not T4 (thyroxine). They say it is more biologically active and makes them feel better. Why am I not prescribed T3?

Although both T4 and T3 are thyroid hormones produced in our bodies, they have different properties. T4 has a longer half life and is converted into T3 in our blood and different tissues. The way our thyroid normally achieves appropriate levels of thyroid hormone is to secrete predominantly T4, and this is converted gradually to T3, as needed, in a regulated manner. T3 is more biologically active but can also rapidly increase heart rate and blood pressure and hence can be dangerous in certain patients, especially older patients or patients with one or more risk factors for heart disease. There is active interest in combining small amounts of T3 with T4 to see if patients feel better, and scientific investigation of these experimental treatment options is underway. For more information, see the section on Optimal Thyroid Hormone Replacement.

I just had a baby and my doctor says I have postpartum thyroiditis, hypothyroidism, and I need to take thyroid hormone. I don't want to stop breastfeeding. Is this a problem?

Postpartum thyroiditis (thyroid inflammation after pregnancy) is a common condition that may become apparent several months after giving birth. There is generally an initial hyperthyroid phase, and in the majority of women, thyroid hormone levels will subsequently return to normal. In some patients, persistent hypothyroidism may develop after the hyperthyroid phase resolves. If after several months, the TSH is not slowly improving, thyroid hormone replacement should be considered. Thyroid hormone replacement has no effect on nursing which need not be stopped. Nursing mothers should not, however, continue breast feeding while undergoing any nuclear medicine diagnostic tests, as the isotope can be passed through to the baby in breast milk. In many instances, nuclear medicine studies can be deferred until breast feeding is electively discontinued.

My TSH is normal but I have a low free T4. Is this possible?

Some patients may have thyroid hormone binding protein abnormalities that can produce abnormal thyroid function tests. Rarely, patients may have problems with their pituitary or hypothalamus that render the TSH less useful as a test for thyroid function. Most patients with a low free T4 but normal TSH simply have lower levels of binding proteins but overall, thyroid function is usually normal.

I have a slight TSH elevation and kidney disease. Is there a benefit to taking thyroid hormone?

There is very little rigorous data to answer this question. One observational study of Korean subjects with subclinical hypothyroidism and stage 2-4 chronic kidney disease revealed that patients taking thyroid hormone had slower declines in renal function over ~ 3 years, however it remains uncertain as to the true benefit achieved that can be attributed to thyroid hormne in this patient population. Preservation of Renal Function by Thyroid Hormone Replacement Therapy in Chronic Kidney Disease Patients with Subclinical Hypothyroidism. J Clin Endocrinol Metab. 2012 Jun 20

I have been taking thyroid hormone for years. Do I have to stay on it forever or can I stop?

The answer to this question depends on why you were started on thyroid hormone in the first place. In some cases, if the reason for starting the thyroid hormone treatment was not clear, in consultation with your physician, it may be possible to stop thyroid hormone for a trial period of several weeks-months and see if your own thyroid gland can resume functioning normally.

I have read that kelp or iodine is good for hypothyroidism but my doctor told me to stop taking it, why?

In patients with iodine deficiency, kelp or iodine supplementation may be beneficial in reducing the size of a goiter and in improving thyroid function. Nevertheless, depending on where one lives, iodine deficiency may not be a problem, and excess iodine can precipitate thyroid disease, either hypo or hyperthyroidism.

I was treated for Hodgkin's disease many years ago. Am I at risk for the development of hypothyroidism?

Patients receiving radiation in the region of the neck for Hodgkin's disease are at increased risk for hypothyroidism and the development of thyroid nodules and thyroid cancer. See Abnormalities of the thyroid in survivors of Hodgkin's disease: data from the Childhood Cancer Survivor Study J Clin Endocrinol Metab 2000 Sep;85(9):3227-32.

My cholesterol is elevated. Will it return to normal after treatment of my hypothyroidism?

Most patients with an elevated TSH will have a small reduction in total cholesterol and HDL levels once their hypothyroidism is appropriately corrected. Although the occasional patient with elevated cholesterol levels may experience a large reduction or complete correction of lipid abnormalities once thyroid status is normalized, in the majority of patients studied, the reductions of cholesterol to be expected are in the range of 5-10%. See J Clin Endocrinol Metab 2000 Sep;85(9):2993-3001 or see Heart Disease.

I am pregnant and taking thyroid hormone. Do I need to worry about my baby?

Thyroid hormone (L-thyroxine) is safe to take during pregnancy. Very little L-thyroxine crosses the placenta, and the baby makes its own thyroid hormone generally by 10-11 weeks of gestation. As pregnancy and the associated weight gain frequently results in an increased required for thyroid hormone, women should have their TSH and Free T4 monitored several times during their pregnancy, as it is quite common to require an increase in the dose of L-thyroxine very early during pregnancy. For more information, see Pregnancy. Interested in learning more about the effects of the mother thyroid status on the health and development of the baby? Participate in a current thyroid study in Toronto at the Hospital for Sick Children.

My TSH is slightly elevated, but I feel fine. My doctor says taking thyroid hormone may be good for my heart. Why?

There is some evidence that even mild deficiency of thyroid hormone may adversely affect the levels of cholesterol. Furthermore, there is also evidence for a modest impairment of heart function in some patients with mild hypothyroidism. These issues should be discussed on an individual basis with your physician. See Cardiovascular and atherogenic aspects of subclinical hypothyroidism. Thyroid. 2000 Aug;10(8):665-79 and Effect of thyroid hormones on cardiac function, geometry, and oxidative metabolism assessed noninvasively by positron emission tomography and magnetic resonance imaging. J Clin Endocrinol Metab. 2000 May;85(5):1822-7  and Left ventricular diastolic dysfunction in patients with subclinical hypothyroidism. J Clin Endocrinol Metab. 1999 Jun;84(6):2064-7. Many thyroid experts feel that the available evidence supports the treatment of mild "subclinical hypothyroidism, as outlined in Subclinical Hypothyroidism Is Mild Thyroid Failure and Should be Treated. J Clin Endocrinol Metab. 2001 Oct;86(10):4585-90.

For more information, also see the section on Heart Disease.

I was just diagnosed with hypothyroidism, and my major complaint is pain in my wrist and hand. Is this related?

Musculoskeletal complaints are common in patients with both hypo and hyperthyroidism, as outlined in Musculoskeletal manifestations in patients with thyroid disease. Clin Endocrinol (Oxf). 2003 Aug;59(2):162-7. Some patients with hypothyroidism may develop a condition known as carpal tunnel syndrome. Fluid retention associated with hypothyroidism may sometimes be localized and compress the nerves (the median nerve control muscles and sensation in the hand) that run through the "carpal tunnel", an anatomical area that connects your wrist to your hand. In many patients, resolution of the hypothyroidism may lead to gradual improvement of the carpal tunnel syndrome (wrist and hand pain, and sometimes weakness of the affected muscles). The diagnosis may sometimes be made clinically, and often specialized nerve testing is required. In many patients physiotherapy and wrist splints may be helpful. Occasionally, surgery may be required if less interventional treatments are not completely effective. The interpretation of muscle weakness in the hand can be difficult, as hypothyroidism may also directly affect the muscles, without affecting the nerves. Furthermore, many patients with normal thyroid function but a history of hypothyroidism will continue to have similar complaints. To review several studies, see Neuromuscular findings in thyroid dysfunction: a prospective clinical and electrodiagnostic study. J Neurol Neurosurg Psychiatry. 2000 Jun;68(6):750-5. and The effects of hypothyroidism and thyroid replacement on the development of carpal tunnel syndrome. J Hand Surg [Am]. 2000 Jul;25(4):734-9.

I had radiation to my brain for cancer therapy. Am I at risk for the development of thyroid problems?

Depending on the amount of Radiotherapy (RT) and the radiation field, there appears to be an increased risk of hypothyroidism in patients exposed to radiation with possible involvement of the hypothalamus and/or pituitary. See Cranial irradiation and central hypothyroidism. Trends Endocrinol Metab. 2001 Apr 1;12(3):97-104.

I have been severely hypothyroid for many months, and I feel exhausted, mentally slow, and depressed. Can these symptoms all be due to the hypothyroidism?

In patients with very severe hypothyroidism, it is certainly possible to have problems with depression, cognitive function, memory, and anxiety. Analysis of cognitive function in hypothyroid subjects has demonstrated measurable changes in electrophysiological markers of cognitive activity and conventional assessments of cognitive function, with significant improvements noted in verbal memory, visual memory, and total memory scores in thyroxine treated patients. See Changes of event related potential and cognitive processes in patients with subclinical hypothyroidism after thyroxine treatment. Endocr Regul. 2002 Sep;36(3):115-22. Newer sophisticated techniques such as positron emission tomography have documented significant changes in brain blood flow and brain energy utilization in the hypothyroid states. Most patients will experience improvement in these thyroid-related symptoms with treatment of the hypothyroidism. See Cerebral blood flow and glucose metabolism in hypothyroidism: a positron emission tomography study. J Clin Endocrinol Metab. 2001 Aug;86(8):3864-70.

One of my relatives is ill in the intensive care unit and the doctors say the thyroid tests are abnormal, but they are not suggesting treatment with thyroid hormone-Why not?

Severe illness is associated with a large number of changes in thyroid hormone production, conversion of T4 to T3, thyroid hormone binding, and TSH secretion. Interpretation of thyroid function tests in a severely ill patient can be challenging. Several studies have been carried out to assess the merits of treating patients with abnormal lab values in the intensive care unit, without clear cut evidence of benefit. For an overview, see The controversy of the treatment of critically ill patients with thyroid hormone. Best Pract Res Clin Endocrinol Metab. 2001 Dec;15(4):465-78.

Can patients ever develop a serious brain condition as a result of hypothyroidism?

A condition known as "Hashimoto's encephalopathy has been described in patients with positive thyroid antibodies, characterized by severe confusion, abnormal mental function, often leading to coma, and abnormal EEG findings. This condition is extremely rate, and often responds to treatment with glucocorticoids. See Rarity of encephalopathy associated with autoimmune thyroiditis: a case series from mayo clinic from 1950 to 1996. Thyroid. 2002 May;12(5):393-8. and Reversible white matter alterations in encephalopathy associated with autoimmune thyroid disease. J Neurol. 2002 Jul;249(8):1063-5. For a review of over 60 cases published in the literature, see Hashimoto encephalopathy: syndrome or myth? Arch Neurol. 2003 Feb;60(2):164-71.

I have symptoms of lung irritation and cough-is this related to my hypothyroidism?

Although there is little evidence linking airway or lung disease with thyroid dysfunction, some studies have detected that symptoms of lung disease are more common in patients with hypothyroidism Airway function and markers of airway inflammation in patients with treated hypothyroidism. Thorax. 2005 Mar;60(3):249-53