Condition Overview

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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.

What is hypothyroidism?

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.

What causes hypothyroidism?

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.

What are the symptoms?

Hypothyroidism can cause many different symptoms, such as:

• Feeling tired, weak, or depressed.
• Dry skin and brittle nails.
• Not being able to stand the cold.
• Constipation.
• Memory problems or having trouble thinking clearly.
• Heavy or irregular menstrual periods.

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.

How is hypothyroidism diagnosed?

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.

How is it treated?

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.

Cause

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:

• Thyroid surgery. Part or all of the thyroid gland may be removed to treat disorders such as having too much thyroid hormone (hyperthyroidism), an enlarged thyroid gland (goiter) that makes swallowing difficult, thyroid cancer, or thyroid nodules that may be overactive or cancerous. Hypothyroidism results when the thyroid gland is removed or when remaining thyroid tissue does not function properly.
• Radioactive iodine therapy, which is often used to treat hyperthyroidism. Radioactive iodine therapy can destroy the thyroid gland, leading to hypothyroidism.
• External beam radiation, which is used to treat some cancers, such as Hodgkin lymphoma. This radiation treatment can destroy the thyroid gland.

Less common causes include:

• Infections. Viral and bacterial infections can temporarily damage the thyroid gland. This causes a short-term form of the condition. Hypothyroidism caused by infection usually does not result in permanent hypothyroidism.
• Medicines. Some medicines can interfere with normal production of thyroid hormone. Lithium is one of the most common medicines that causes hypothyroidism. Others include amiodarone and interferon alfa (such as Intron A).
• In rare cases, disorders of the pituitary gland or the hypothalamus (secondary and tertiary forms of hypothyroidism). The pituitary gland and hypothalamus produce hormones that control the thyroid and, as a result, affect its ability to produce thyroid hormone.
• Excessive iodine, which, in food or medicines, can reduce the function of the thyroid gland. This is usually temporary.
• Congenital hypothyroidism. In rare cases, an infant is born without a properly functioning thyroid gland. All children born in a hospital in Canada are tested at birth for hypothyroidism.

Symptoms

Symptoms of hypothyroidism usually appear slowly over months or years. Symptoms and signs may include:

• Coarse and thinning hair.
• Dry skin.
• Brittle nails.
• A yellowish tint to the skin.
• Slow body movements.
• Cold skin.
• Inability to tolerate cold.
• Feeling tired, sluggish, or weak.
• Memory problems, depression, or problems concentrating.
• Constipation.
• Heavy or irregular menstrual periods that may last longer than 5 to 7 days.

Some less common symptoms may include:

• An enlarged thyroid gland (goiter).
• Modest weight gain, often 4.5 kg (10 lb) or less.
• Swelling of the arms, hands, legs, and feet, and facial puffiness, particularly around the eyes.
• Hoarseness.
• Muscle aches and cramps.

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.

Symptoms of hypothyroidism in infants, children, and teens

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.

What Happens

Untreated hypothyroidism may get better or worse over time, depending on its cause and your age.

Hypothyroidism in infants and children

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 in adults

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:

• Myxedema, a condition that causes swelling of tissues, increased fluid around the heart and lungs, slowed muscle reflexes, and a slowed ability to think.
• Myxedema coma, a rare, life-threatening condition. This can occur if you have had hypothyroidism for many years that becomes markedly worse. It usually occurs when older adults who have severe hypothyroidism become ill with another condition, suffer from cold exposure, or take painkillers or sleeping pills. Symptoms include mental deterioration, such as apathy, confusion, and psychosis. You may lose consciousness (coma) and may have an extremely low body temperature (hypothermia), slow heartbeat (fewer than 60 beats per minute), heart failure, and trouble breathing.
• Complications, such as:
  • Increased levels of cholesterol and triglycerides (increasing the risk of coronary artery disease and stroke).
  • Fluid around the heart (pericardial effusion).
  • Sleep apnea, which causes you to stop breathing for 10 seconds or longer while sleeping.
  • A decrease in mental abilities.

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.

Hypothyroidism during and after pregnancy

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.

What Increases Your Risk

Many things may increase your risk for hypothyroidism. These include:

• Age and being female. Older adults are more likely to develop hypothyroidism than younger people. And women are more likely than men to develop thyroid disease.
• 
  Family history
  . Hypothyroidism tends to run in families.
• Previous thyroid problems. Thyroid disease, an enlarged thyroid (goiter), and surgery or radiation therapy to treat thyroid problems increase the likelihood of having hypothyroidism in the future.
• Some lifelong conditions. Type 1 diabetes, vitiligo (an autoimmune disease that causes patches of light skin), pernicious anemia, and leukotrichia (premature grey hair) are seen more often in people who have hypothyroidism.
• Iodine deficiency. This is rare in Canada but common in areas where iodine is not added to salt, food, and water.
• Medicines. Some medicines can interfere with normal thyroid function, particularly lithium, amiodarone, and interferon alfa.

When To Call

Call
911
or other emergency services immediately if you or a person you know has hypothyroidism and has signs of myxedema coma, such as:

• Mental deterioration, such as apathy, confusion, or psychosis.
• Extreme weakness and fatigue that progress to loss of consciousness (coma).
• Severe trouble breathing, slow heart rate (less than 60 beats per minute), or low body temperature [35°C (95°F) or below].

See your doctor if you have any symptoms that don't go away, including:

• Depression
• Feeling tired, sluggish, or weak.
• Memory problems or trouble concentrating.
• An inability to tolerate cold.
• Dry skin, brittle nails, or a yellowish tint to the skin.
• Constipation.
• Heavy or irregular menstrual periods that may last longer than 5 to 7 days.

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's 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

Watchful waiting is a wait-and-see approach. It's not a good choice for hypothyroidism that is causing symptoms. Treatment should start as soon as the condition is diagnosed.

Watchful waiting may be okay for certain adults with mild (subclinical) hypothyroidism whose blood tests show only small changes. Talk to your doctor about treatment 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.

Examinations and Tests

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:

• Thyroid-stimulating hormone (TSH) test.
• Free Thyroxine (FT4) measurement.

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.

Early detection

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:

• People with one or more close relatives who have or had hypothyroidism.
• People with conditions associated with Hashimoto's thyroiditis, including Addison's disease, rheumatoid arthritis, pernicious anemia, and type 1 diabetes.
• Pregnant women. In pregnant women known to have hypothyroidism, tests should be done at regular intervals to determine whether the dosage of thyroid hormone medicine is adequate.
• Women who are having symptoms of hypothyroidism after pregnancy (postpartum hypothyroidism), such as depression, memory and concentration problems, or thyroid enlargement (goiter). Women who have had hypothyroidism during or after pregnancy should be retested if they become pregnant again.

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}

Treatment Overview

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.

• If you have had radiation therapy and have hypothyroidism, or if your thyroid gland has been removed, you will most likely need treatment from now on. If your hypothyroidism is caused by Hashimoto's thyroiditis, you might also need treatment from now on. Sometimes, thyroid gland function returns on its own in Hashimoto's thyroiditis.
• If a serious illness or infection triggered your hypothyroidism, your thyroid function most likely will return to normal when you recover.
• Some medicines may cause hypothyroidism. Your thyroid function may return to normal when you stop the medicines.
• If you have mild (subclinical) hypothyroidism, you may not need treatment but should be watched for signs of hypothyroidism getting worse. You and your doctor will talk about the pros and cons of taking medicine to treat your mild hypothyroidism. The dose of thyroid medicine must be watched carefully in people who also have heart disease, because too much medicine increases the risk of chest pain (angina) and irregular heartbeats (atrial fibrillation).

Initial treatment

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.

• If you develop hypothyroidism during pregnancy, treatment should be started immediately. If you have hypothyroidism before you become pregnant, your thyroid hormone levels need to be checked to make sure that you have the right dose of thyroid medicine. During pregnancy, your dose of medicine may need to be increased by 25% to 50%.^{footnote 3}
• If you develop hypothyroidism after pregnancy (postpartum hypothyroidism), you also may need treatment. You will be retested for hypothyroidism if you become pregnant again. In some cases hypothyroidism will go away on its own. In other cases it is permanent and requires lifelong treatment.

Ongoing treatment

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.

Treatment if the condition gets worse

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.

Prevention

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:

• The Canadian Task Force on the Periodic Health Examination and the U.S. Preventive Services Task Force make no recommendation for or against thyroid screening for people who do not have symptoms of hypothyroidism. They state there is not enough evidence to support screening.^{footnote 4, footnote 5}
• The American Thyroid Association recommends that testing be considered for those older than age 60.^{footnote 6}
• Another panel of experts from several medical specialties recommends against widespread screening.^{footnote 7} But these health professionals say that if you are high risk, you may want to be screened. Those at high risk include women older than age 60 and people who have type 1 diabetes or other autoimmune diseases. Talk to your doctor about whether you should be screened.

Talk to your doctor about whether testing is right for you.

Self-Care

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.

Medicines

Thyroid hormone medicine is the only effective way to treat hypothyroidism. In most cases, thyroid hormone medicine:

• Reduces or eliminates symptoms of hypothyroidism. Symptoms usually improve within the first week after you begin therapy. All symptoms usually disappear within a few months.
• May reduce the risk of slowed physical growth, intellectual disability, and behavioural problems in infants and children.

Thyroid hormone medicine does not cause side effects if you take the correct dose.

What to think about

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.