Examples

Generic Name	Brand Name
desiccated thyroid (not recommended for replacement therapy)	Armour Thyroid
levothyroxine sodium (T4)	Levothroid, Levoxyl, Synthroid
liothyronine sodium (T3)	Cytomel
liotrix (T3 and T4)	Euthroid, Thyrolar

Thyroid hormones are taken by mouth (orally) except in unusual cases, such as myxedema coma. That condition requires intravenous (IV) medication. 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 medication replaces missing hormones.

Why It Is Used

Thyroid hormone medications are given when blood tests indicate you have hypothyroidism.

Thyroid hormone medications 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 medication 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 medication works quickly to correct symptoms.

Myxedema coma can respond well to thyroid hormone medication and treatment in an intensive care unit. However, 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 medication.

Side effects of too much thyroid hormone 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 health professional.

If you have coronary artery disease and take too much thyroid medication, 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. If you have trouble taking your thyroid medication as prescribed, talk to your health professional.

Keep follow-up visits with your health professional to make sure you are taking the medication correctly. Your health professional also may need to adjust your dose. Most people return to their health professional 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.

Taking calcium supplements and thyroid medication at the same time may reduce the amount of thyroid medication your body gets. Take calcium supplements at least 4 hours before or after taking thyroid hormone medication.¹

If you take birth control pills or other hormones, talk to your health professional about whether you need to change your dose of thyroid medication. You may need to take more medication than you would if you were not taking these hormones.

Certain medications can affect the way thyroid medications work. People taking the following medications need to see their health professional often to make sure they are getting the correct dose of thyroid hormone medication.

• Cholestyramine, ferrous sulfate, sucralfate, and some antacids containing aluminum hydroxide often interfere with the absorption of levothyroxine.
• Seizure medication (anticonvulsants) and an antibiotic used to treat tuberculosis (rifampin) may speed the breakdown of levothyroxine, making it necessary to take a higher dose.

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 mental retardation from hypothyroidism, thyroid hormone medication will control symptoms of hypothyroidism but will not reverse the mental disabilities.

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

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.

Citations

1. Singh N, et al. (2000). Effects of calcium carbonate on the absorption of levothyroxine. JAMA, 283(21): 2822–2825.