Examples

Thyroid hormones are taken by mouth (orally) except in unusual cases, such as myxedema coma. That condition requires intravenous (IV) medicine. Dosages vary with the person's age and the severity of the disease.

How It Works

People with hypothyroidism have lower-than-normal or no thyroid function and do not make enough thyroid hormone for the body to function properly. Taking thyroid hormone medicine replaces missing hormones.

Why It Is Used

Thyroid hormone medicines are given when blood tests show that you have hypothyroidism.

Thyroid hormone medicines also may be prescribed:

• For mild (subclinical) hypothyroidism when you test positive for antithyroid antibodies.
• For an enlarged thyroid gland (goiter).

How Well It Works

People with hypothyroidism who take thyroid hormone medicine usually notice:

• Improved energy level.
• Gradual weight loss (in people with severe hypothyroidism at the time of diagnosis).
• Improved mood and mental function (thinking, memory).
• Improved pumping action of the heart and improved digestive tract function.
• Reduction in the size of an enlarged thyroid gland (goiter), if you have one.
• Improved growth, school performance, and behavior in children. Children whose growth has been delayed because of hypothyroidism start growing normally again once they get adequate doses of thyroid hormone.
• Lower cholesterol and triglyceride levels.

In most cases, thyroid hormone medicine works quickly to correct symptoms.

Myxedema coma can respond well to thyroid hormone medicine and treatment in an intensive care unit. But a good outcome depends on how soon treatment starts.

Side Effects

In general, you will not have side effects if you are taking the correct amount of thyroid hormone medicine.

Side effects of too much thyroid medicine include:

• Heart palpitations.
• Nervousness.
• Trouble sleeping (insomnia).
• Shaking (tremors).
• Frequent bowel movements.
• Too much weight loss.
• Discomfort in warm weather.
• Bone thinning (osteoporosis) if the dose is too high for a long time.

Report any side effects to your doctor.

If you have coronary artery disease and you take too much thyroid medicine, symptoms such as chest pain (angina) or heart rhythm irregularities (arrhythmia) may get worse. Also, you may have an increased risk of heart attack.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Thyroid hormones work best when they are taken as prescribed. It is best to take your thyroid medicine on an empty stomach. If you have trouble taking your thyroid medicine as prescribed, talk to your doctor.

Keep follow-up visits with your doctor to make sure you are taking the medicine correctly. Your doctor also may need to adjust your dose. Most people return to their doctor for blood tests to measure hormone levels 6 to 8 weeks after starting therapy. After thyroid hormone levels have returned to normal, thyroid function tests are checked once a year.

Certain medicines can affect the way thyroid medicines work. People taking the following medicines need to see their doctor often to make sure they are getting the correct dose of thyroid hormone medicine. Some of these medicines include:

• Calcium. Take calcium supplements at least 4 hours before or after taking thyroid hormone medicine.
• Iron supplements.
• Birth control pills or other hormones.
• Cholestyramine.
• Sucralfate and some antacids containing aluminum hydroxide.
• Some seizure medicines.

People with Hashimoto's thyroiditis, the most common cause of hypothyroidism, often need treatment for the rest of their lives.

People who have other health conditions in addition to hypothyroidism, particularly coronary artery disease, may sometimes develop problems if they are started on a large dose of thyroid hormone. These people are often started on a lower dose that is carefully increased.

If an infant has intellectual disability from hypothyroidism, thyroid hormone medicine will control symptoms of hypothyroidism but will not reverse the intellectual disabilities.

Too much thyroid hormone medicine can increase bone loss (osteoporosis).

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