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This topic provides information about hypothyroidism. Hypothyroidism means your thyroid is not making enough thyroid hormone. If you are looking for information about when the thyroid makes too much thyroid hormone, see the topic Hyperthyroidism.
Hypothyroidism means your thyroid is not making enough thyroid hormone. The thyroid is a butterfly-shaped gland in the front of your neck. It makes hormones that control the way your body uses energy.
Having a low level of thyroid hormone affects your whole body. It can make you feel tired and weak. If hypothyroidism is not treated, it can raise your cholesterol levels. During pregnancy, untreated hypothyroidism can harm your baby. But hypothyroidism can be treated with medicine that can help you feel like yourself again.
People of any age can get hypothyroidism, but older adults are more likely to get it. Women age 60 and older have the highest risk. You are more likely to get the disease if it runs in your family.
In Canada, the most common cause is Hashimoto's thyroiditis. It causes the body's immune system to attack thyroid tissue. As a result, the gland can't make enough thyroid hormone.
Other things that can lead to low levels of thyroid hormone include surgery to remove the thyroid gland and radiation therapy for cancer. Less common causes include viral infections and some drugs, such as amiodarone and lithium.
Hypothyroidism can cause many different symptoms, such as:
Symptoms occur slowly over time. At first you might not notice them, or you might mistake them for normal aging. See your doctor if you have symptoms like these that get worse or won't go away.
Your doctor will ask questions about your symptoms. You will also have a physical examination. If your doctor thinks you have hypothyroidism, a simple blood test can show if your thyroid hormone level is too low.
Doctors usually prescribe pills to treat hypothyroidism. Most people start to feel better in a week or two. Your symptoms will probably go away within a few months. But you will likely need to keep taking the pills from now on.
It's important to take your medicine just the way your doctor tells you to. You will also need to see your doctor for follow-up visits to make sure you have the right dose. Getting too much or too little thyroid hormone can cause problems.
If you have mild hypothyroidism, you may not need treatment now. But you'll want to watch for signs that it is getting worse.
If you are diagnosed with severe hypothyroidism, you will need to be treated right away in the hospital. Severe hypothyroidism can lead to a rare but dangerous disease called myxedema coma.
In Canada, the most common cause of hypothyroidism is Hashimoto's thyroiditis. This is a condition that causes the body's natural defenses—the immune system—to produce antibodies that over time destroy thyroid tissue. As a result, the thyroid gland cannot make enough thyroid hormone.
Worldwide, iodine deficiency is the number one cause of hypothyroidism. But iodine added to salt, food, and water has nearly eliminated this problem in Canada and other Western countries.
Other common causes of hypothyroidism include:
Less common causes include:
Symptoms of hypothyroidism usually appear slowly over months or years. Symptoms and signs may include:
Some less common symptoms may include:
In general, how bad your symptoms are depends on your age, how long you have had hypothyroidism, and the seriousness of the condition. The symptoms may be so mild and happen so slowly that they go unnoticed for years.
Mild (subclinical) hypothyroidism often causes no symptoms or vague symptoms that may be attributed to aging, such as memory problems, dry skin, and fatigue.
Symptoms of hypothyroidism during and after pregnancy include fatigue, weight loss, dizziness, depression, and memory and concentration problems.
Because of the range of symptoms, hypothyroidism can be mistaken for depression, especially during and after pregnancy. In older people, it may be confused with Alzheimer's disease, dementia, and other conditions that cause memory problems.
Although rare, hypothyroidism can occur in infants, children, and teens. In infants, symptoms of a goiter include a poor appetite and choking on food. Symptoms of hypothyroidism may include dry, scaly skin. In children and teens, symptoms include behaviour problems and changes in school performance. Children and teens may gain weight and yet have a slowed growth rate. Teens may have delayed puberty and look much younger than their age.
Untreated hypothyroidism may get better or worse over time, depending on its cause and your age.
Although rare, hypothyroidism can occur in infants and children. If hypothyroidism is treated within the first month of life, a child will grow and develop normally. Untreated hypothyroidism in infants can cause brain damage, leading to intellectual disability and developmental delays. In Canada, all children are tested for hypothyroidism at birth.
Intellectual disability usually does not occur if hypothyroidism develops after age 3. But untreated childhood hypothyroidism typically delays physical growth and sexual development, including the onset of puberty. Children may gain weight yet have a slowed growth rate.
Hypothyroidism caused by Hashimoto's thyroiditis sometimes will disappear on its own. More often, the disorder causes a gradual loss of thyroid function. Your symptoms may develop slowly and be so mild that you do not notice them for years. But symptoms usually grow worse. And health problems may develop as the disease continues.
If untreated, hypothyroidism may lead to:
People with mild (subclinical) hypothyroidism have only slightly abnormal thyroid blood test results and often do not have obvious symptoms or health problems. Some people who have mild hypothyroidism regain normal thyroid function.
If your thyroid gland has been removed during surgery, hypothyroidism will occur within a few weeks. If you have been treated with radioactive iodine therapy, hypothyroidism may develop within a year. In these cases, thyroid function typically does not return, and you will need to take thyroid hormone medicine from now on.
Women who have hypothyroidism or mild hypothyroidism before they become pregnant may have more severe hypothyroidism during their pregnancy. If not treated, pregnant women who have hypothyroidism can develop pre-eclampsia and have a premature delivery. Children born to women who have untreated hypothyroidism during pregnancy are at risk for having hypothyroidism at birth and low birth weight and may score lower on intelligence tests than children of healthy mothers.footnote 1
After delivery, women may have a thyroid disorder called postpartum thyroiditis. This condition occurs in about 5% of women who do not have a history of thyroid disease.footnote 1 It is often mistaken for depression.
Women who have postpartum thyroiditis often develop hypothyroidism 3 to 6 months after delivery. The hypothyroidism may last up to several months. It sometimes occurs after an initial episode of postpartum thyroiditis that causes symptoms from too much thyroid hormone. Hypothyroidism may become permanent in women with postpartum thyroiditis. Even if thyroid gland function returns to normal, postpartum thyroiditis usually comes back during later pregnancies.
Many things may increase your risk for hypothyroidism. These include:
Call 911 or other emergency services immediately if you or a person you know has hypothyroidism and has signs of myxedema coma, such as:
See your doctor if you have any symptoms that don't go away, including:
If you have one or two of the above symptoms that have not changed or have changed very little over a long period of time, it is less likely that the symptoms are caused by hypothyroidism. Consult your doctor.
Talk to a doctor if you are pregnant and have some of the above symptoms. Also talk to a doctor if you have hypothyroidism and are pregnant or are trying to become pregnant. Your dose of thyroid hormone medicine may need to be changed.
Watchful waiting—a period of time during which you and your doctor observe your symptoms or condition without using medical treatment—is not appropriate for hypothyroidism that is causing symptoms. Treatment should begin as soon as the condition is diagnosed.
Watchful waiting may be appropriate for certain adults with mild (subclinical) hypothyroidism whose blood tests show only modest changes. Talk to your doctor about treatment, its cost and possible risks and benefits. Watch for any signs that your hypothyroidism is getting worse. Doctors often want people to have yearly thyroid function blood tests to check to see if thyroid hormone production is normal.
Hypothyroidism can be diagnosed by a:
Hypothyroidism also may be diagnosed by a specialist, such as a gastroenterologist, gynecologist, or psychiatrist, depending on the symptoms you have and who you see to evaluate the symptoms.
Complicated or unusual cases of hypothyroidism may require consultation with an endocrinologist.
A thorough medical history and physical examination are the first steps in diagnosing hypothyroidism or mild (subclinical) hypothyroidism. If the results lead your doctor to suspect you have hypothyroidism or subclinical hypothyroidism, you will have tests to confirm the diagnosis.
Blood tests are always used to confirm a diagnosis of hypothyroidism or mild hypothyroidism. The tests used most often are:
If the above tests are not normal, antithyroid antibody tests may determine whether you have the autoimmune disease Hashimoto's thyroiditis, in which the body's defense system attacks the thyroid gland.
In rare cases, a thyroid ultrasound may be used to evaluate a thyroid gland that during a physical examination seems to be abnormal.
A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the hypothalamus or pituitary gland may be done to look for any changes in these areas of the brain.
Because of the possibility of intellectual disability in infants with hypothyroidism, every province in Canada tests newborns for hypothyroidism. If your baby was not born in a hospital, or if you believe your baby may not have been tested, talk to your doctor. Screening tests for hypothyroidism are not always accurate. Even if test results show no problem, watch your child for symptoms of hypothyroidism, such as poor appetite, not gaining weight, and dry skin.
Some doctors now recommend routine testing for people at risk for hypothyroidism, including:
Not all experts agree on whether to recommend widespread screening for hypothyroidism. Some groups say there is not enough evidence of benefit to recommend screening for everyone. But people who are at high risk—women older than 60 and anyone with a family history of thyroid disease or who has other autoimmune diseases—may want to be screened.footnote 2
Hypothyroidism can be easily treated using thyroid hormone medicine. The most effective and reliable thyroid replacement hormone is man-made (synthetic). After starting treatment, you will have regular visits with your doctor to make sure you have the right dose of medicine.
In most cases, symptoms of hypothyroidism start to improve within the first week after you start treatment. All symptoms usually disappear within a few months. Infants and children with hypothyroidism should always be treated. Older adults and people who are in poor health may take longer to respond to the medicine.
Your doctor will treat your hypothyroidism with the thyroid medicine levothyroxine (for example, Eltroxin, Euthyrox, or Synthroid). Take your medicine as directed. You will have another blood test 6 to 8 weeks later to make sure the dose is right for you.
If you take too little medicine, you may have symptoms of hypothyroidism, such as constipation, feeling cold or sluggish, and gaining weight. Too much medicine can cause nervousness, problems sleeping, and shaking (tremors). If you have heart disease, too much medicine can cause irregular heartbeats and chest pain. People who also have heart disease often start on a low dose of levothyroxine, which is increased gradually.
If you have severe hypothyroidism by the time you are diagnosed, you will need immediate treatment. Severe, untreated hypothyroidism can cause myxedema coma, a rare, life-threatening condition.
Treatment during pregnancy is especially important, because hypothyroidism can harm the developing fetus.
You are likely to need treatment for hypothyroidism from now on. As a result, you need to take your medicine as directed. For some people, hypothyroidism gets worse as they age and the dosage of thyroid medicine may have to be increased gradually as the thyroid continues to slow down.
Most people treated with thyroid hormone develop symptoms again if their medicine is stopped. If this occurs, medicine needs to be restarted.
If a serious illness or infection triggers your hypothyroidism, your thyroid function most likely will return to normal when you recover. To check whether thyroid function has returned to normal, thyroid hormone medicine may be stopped for a short time. In most people, a brief period of hypothyroidism occurs after thyroid medicine is stopped. There is often a delay in the body's signals that tell the thyroid to start working again. If the thyroid can produce enough hormone on its own, treatment is no longer needed. But if hormone levels remain too low, you need to restart thyroid medicine.
While taking thyroid hormone medicine, you need to see your doctor once a year for checkups. You will have a blood test (thyroid-stimulating hormone [TSH] test) to make sure you have a normal hormone level.
Sometimes symptoms of hypothyroidism continue, such as sluggishness, constipation, confusion, and feeling cold. This may occur if you are not taking enough thyroid hormone or if your medicine is not absorbed from your gastrointestinal tract. Having a bowel disease or taking certain other medicines may block thyroid hormone. If needed, your doctor will increase your dose.
Your doctor may suggest you try the combination therapy of T3/T4 medicine if T4 medicine is not controlling your symptoms.
If your dose of thyroid hormone is too high, you may develop complications such as irregular heartbeats and, over time, osteoporosis. If you have heart disease, too much medicine can cause pain (angina) and irregular heartbeats. Your doctor will watch your thyroid levels using a thyroid-stimulating hormone (TSH) test. If needed, your doctor will lower your dose.
Most cases of hypothyroidism in Canada are caused by Hashimoto's thyroiditis, which cannot be prevented.
Although you can't prevent hypothyroidism, you can watch for signs of the disease so it can be treated promptly. Some people who are at high risk for having hypothyroidism but do not have symptoms can be tested to see whether they have mild, or subclinical, hypothyroidism.
Expert groups differ in their recommendations for screening. For example:
Talk to your doctor about whether testing is right for you.
If you have hypothyroidism, see your doctor once a year so your condition can be closely checked and your treatment adjusted, if needed.
Be sure to take thyroid hormone medicine correctly. Talk with your doctor if you don't understand the reason for taking medicine regularly or if you think you have any side effects from the medicine. You usually need to have regular blood tests to find out whether you are receiving the correct amount of thyroid hormone.
Children who have hypothyroidism also need to see a doctor regularly, because the amount of thyroid hormone medicine they need changes as they grow. Untreated hypothyroidism in infants and very young children can have severe consequences. As soon as you think your child is able to understand (usually around age 9 or 10), teach him or her about hypothyroidism, the importance of taking medicine correctly, and why regular health checkups are important.
Some health food stores in Canada and the United States sell "natural" forms of thyroid hormone. The quality and effectiveness of these natural agents are unregulated. Some may not work at all. Others may have an active ingredient that does work but that may be dangerous to certain people.
Thyroid hormone medicine is the only effective way to treat hypothyroidism. In most cases, thyroid hormone medicine:
Thyroid hormone medicine does not cause side effects if you take the correct dose.
People who have hypothyroidism need treatment with thyroid hormone medicine. Depending on the cause of their hypothyroidism, they may need treatment for the rest of their lives.
Taking certain supplements, such as calcium or iron (or both), at the same time as thyroid hormone medicine may reduce the amount of thyroid hormone medicine absorbed by the body. Take calcium supplements at least 4 hours before or after taking thyroid hormone medicine. Also avoid taking iron supplements at the same time as thyroid medicine.
Talk to your doctor about whether you need to change your dose of thyroid medicine if you also take birth control pills or other hormones. You may need to take more thyroid hormone medicine than you would if you were not taking these hormones.
Follow-up visits with your doctor are important to make sure that you are taking the correct dose of medicine. Most people have blood tests 6 to 8 weeks after starting treatment. After thyroid hormone levels return to normal, thyroid function tests are typically rechecked once a year.
CitationsAmerican College of Obstetricians and Gynecologists (2002, reaffirmed 2010). Thyroid disease in pregnancy. ACOG Practice Bulletin No. 37. Obstetrics and Gynecology, 100(2): 387–396.LeFevre ML (2015). Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement. Annals of Internal Medicine, published online Mar 24, 2015. DOI: 10.7326/M15-0483. Accessed April 10, 2015.Brent GA, Davies TF. (2011). Hypothyroidism and thyroiditis. In S Melmed et al., eds., Williams Textbook of Endocrinology, 12th ed., pp. 406–439. Philadelphia: Saunders.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.U.S. Preventive Services Task Force (2004). Screening for thyroid disease: Recommendation statement. Annals of Internal Medicine, 140: 125–141.Garber JR, et al; American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults (2012). Clinical practice guidelines for hypothyroidism in adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrinology Practice, 18(6): 988–1028.Other Works ConsultedCooper DS, Ladenson PW (2011). The thyroid gland. In DG Gardner, D Shoback, eds., Greenspan's Basic and Clinical Endocrinology, 9th ed., pp. 163–226. New York: McGraw-Hill.Drugs for thyroid disorders (2009). Treatment Guidelines From The Medical Letter, 7(84): 57–64. 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.Nygaard B (2010). Hypothyroidism (primary), search date September 2009. Online version of BMJ Clinical Evidence: http://www.clinicalevidence.com.Villar HCCE, et al. (2007). Thyroid hormone replacement for subclinical hypothyroidism. Cochrane Database of Systematic Reviews (3).
Adaptation Date: 5/19/2020
Adapted By: Alberta Health Services
Adaptation Reviewed By: Alberta Health Services
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