Thyroid hormone replacement is a medication you take to replace hormones if your thyroid isn’t producing enough or if your thyroid has been removed.

Thyroid hormone replacement typically involves taking daily medications to increase your levels of thyroid hormone.

If your thyroid doesn’t produce enough of these hormones, you may need to take thyroid hormone replacement treatment.

These treatments are synthetic hormones produced in a laboratory or dried natural hormones derived from animals’ thyroids.

Depending on your needs, there are different types of thyroid hormone replacement medications. A doctor may prescribe a specific type or a medication that combines two kinds.

Keep reading to learn why you may need to take them, the types of medications available, and potential side effects.

You may need thyroid hormone replacement treatment if you have an underactive thyroid (hypothyroidism), whether due to:

These health conditions are typically permanent. Many people take thyroid hormone replacement medications for life.

Thyroid hormones help regulate the activity of the thyroid. The thyroid produces various hormones to help manage important body functions, such as:

  • metabolic rate, or the rate at which your body uses energy, which can affect weight
  • body temperature
  • heart rate
  • digestion, including how quickly or slowly food moves through your digestive tract
  • muscle contraction
  • brain development
  • production of new skin and bone cells

Medications can provide versions of the active triiodothyronine (T3) and inactive thyroxine (T4) forms of thyroid hormone.

Key terms

Triiodothyronine (T3) is the active form of the thyroid hormone. It has a short life span in the body.

Thyroxine (T4) is a form of the thyroid hormone that the body stores for longer. When needed, the body converts T4 to T3 in the cells. This happens even if you do not have a thyroid.

Thyroid-stimulating hormone (TSH) is a hormone produced by the pituitary gland that tells the thyroid gland how much thyroid hormone to produce. This hormone is regulated by how much thyroid hormone is in the blood.

Typically, an endocrinologist (a doctor specializing in the glands that produce hormones) performs thyroid hormone tests to determine how much T3 and T4 you may need. The thyroid gland typically produces T4 in larger amounts and T3 in smaller quantities.

You may need tests every 4 to 6 weeks initially to help determine the appropriate dose, and then every 6 to 12 months once your dose is established.

Thyroid hormone replacement medications may include synthetic (made in a lab) or porcine (derived from a pig) hormones. They can include:

  • levothyroxine sodium (Synthroid, Levoxyl, Levothroid, Unithroid), a synthetic version of T4
  • liothyronine (Cytomel), a synthetic version of T3
  • liotrix (Thyrolar), a synthetic version of both T3 and T4
  • dessicated natural thyroid (Armour Thyroid, Nature-throid, Westhroid), a dried natural thyroid hormone from a pig

If you don’t already have an endocrinologist, a primary care doctor will typically refer you to one.

If you need thyroid hormone replacement, a doctor typically determines your initial dose based on your individual information. This can include:

  • current thyroid function and the reason you need thyroid hormone replacement
  • weight
  • age
  • other health conditions

You typically receive a dose that regulates your levels of T3, T4, and TSH.

You may have adverse side effects if your levels are too high or too low.

However, doctors may recommend higher doses of thyroid hormone replacement in some people with thyroid cancer that’s at risk of returning. High levels of thyroid hormone can reduce the amount of TSH the pituitary gland produces. This is known as thyroid hormone suppression therapy.

You need to have regular monitoring if you’re taking thyroid hormone replacement. This helps ensure you’re taking the correct dose.

Monitoring may involve tests that measure the amounts of:

You’ll typically need to take your thyroid hormone replacement medication at the same time each day. Doctors usually recommend taking this medication in the morning on an empty stomach, as food can affect how your body absorbs thyroid hormone.

If you take other medications, you’ll have to discuss when to take them with your doctor. Some medications can affect how the body absorbs thyroid hormone replacement.

If you miss a dose of your medication, it’s usually OK to take it as soon as you remember. But if it’s close to your next scheduled dose, skip it and take the next scheduled dose on time.

Do not take two doses to try to make up for the missed dose, as this can lead to more side effects. If you are unsure of what to do, talk with your pharmacist or doctor.

If you miss more than one dose, it’s best to talk with your doctor about how to manage missed doses.

Thyroid hormone replacement typically doesn’t cause side effects. However, you may experience some side effects of thyroid hormone replacement if your dose is too high.

Side effects of too much thyroid hormone replacement may include:

Taking very high levels of thyroid hormone replacement over time may potentially increase your risk of osteoporosis and a rapid or irregular heartbeat. That’s why very high doses are typically only prescribed as part of thyroid-stimulating hormone suppression therapy for certain types of thyroid cancer.

If you experience side effects that may indicate your dose of thyroid hormone replacement may be too high, it’s best to talk with a doctor. They may recommend testing your thyroid hormone levels and adjusting your dose.

Never stop taking prescribed medication without being directed to by the prescribing doctor.

Thyroid hormone replacement treatment is typically covered by most insurance plans, including private insurance and Medicare Part D. The amount you pay out of pocket can depend on your particular plan.

Some plans may cover specific brand-name thyroid hormone replacement medications or only generic options. If your doctor prescribes a treatment that your insurance does not cover, the insurance company may offer you an alternative, such as a generic form. It’s important to let your doctor know which medication your insurance approves and if the drug you receive changes.

Typically, brand-name drugs cost more than generic versions. They may also have slightly different inactive ingredients, which vary between brands.

If you do not have insurance coverage for your medication, you can often find manufacturer coupons for brand-name drugs like Synthroid or Unithroid that may lower the cost.

An endocrinologist may prescribe thyroid hormone replacement if your thyroid hormone levels are too low. This may happen due to hypothyroidism, after treatment for hyperthyroidism, or after surgical removal of your thyroid gland.

Thyroid hormone replacement usually involves medications that you take at the same time each day.

Your prescribing doctor will likely monitor your thyroid hormone levels over time to make sure you’re taking the right dose.