Thyroid hormone therapy is the use of manmade thyroid hormones to raise low levels of natural thyroid hormones in the body.

Thyroid hormone is usually given in pill form. It’s often used to treat an underactive thyroid. This is a thyroid that secretes little or no thyroid hormones. The most commonly prescribed thyroid hormone replacement is pure synthetic thyroxine (T4).

Who needs thyroid hormone replacement therapy?

Thyroid hormone therapy is prescribed when your thyroid doesn’t make enough thyroid hormone naturally. This is a condition referred to as hypothyroidism. It’s the most common reason people need hormone therapy. Other reasons for using thyroid hormone therapy may rarely include:

  • To control the growth of the enlarged thyroid gland (also called goiter);
  • To control the growth of nodules on the thyroid gland;
  • Treatment after the removal of the thyroid for cancerous or noncancerous disease;
  • After treatment of hyperthyroidism by radioactive iodine ablation.

How is thyroid hormone replacement therapy dosage determined?

Healthcare providers do careful blood testing to find the best dose of hormone replacement therapy for each person. The blood tests show levels of thyroid hormones in the blood, as well as thyroid-stimulating hormone (TSH) released by the pituitary gland.

The pituitary gland plays a key role in how the thyroid gland works. It controls how much thyroid hormone is released by making TSH “stimulate” the thyroid. Increased levels of TSH may mean that you have an underactive thyroid or that thyroid hormone replacement needs to be increased.

You will have lab tests to measure levels of thyroid hormones and TSH. Hypothyroidism can get worse over time. This means the dose may need to be increased over time. People over age 60 usually start thyroid hormone at a lower dose to be sure they can handle the medicine.

To make sure that your thyroid hormone replacement works, consider the following:

Have routine visits with a healthcare provider.

Take your thyroid medicine at least 1 hour before breakfast and any calcium or iron medicines you may take. Or take your medicine at bedtime, or at least 3 hours after eating, or taking any calcium or iron medicines. If you forget to take your thyroid medicine at your regular time, take it as soon as you can, but do not take a double dose the next day.

Always stay with the same brand of thyroid medicine. Talk to a healthcare provider before switching to another brand of medicine.

Tell other healthcare providers about your thyroid hormone treatment before starting treatment for any other disease. Some treatments for other conditions or diseases can affect the dosage of thyroid hormone therapy.

  • Let a healthcare provider know if you become pregnant.
  • Tell a healthcare provider if you have any new symptoms.
  • Tell all healthcare providers of your thyroid condition and medicine dosage.

Medications Used to Treat Thyroid Disease

Thyroid medications encompass an array of different options, which differ not only in their composition but their intent. Hormone replacement therapy, such as Synthroid (levothyroxine), is the most widely used drug for hypothyroidism. An anti-thyroid drug-like Tapazole (methimazole) may be used for hyperthyroidism, and thyroid cancer patients may require or radioactive-iodine therapy or chemotherapy.

They all, however, have one thing in common: Treatment with them must be optimized in order to adequately manage your thyroid disease.

What is hypothyroidism?

Hypothyroidism Medications

The role of the thyroid gland is to produce the hormones thyroxine (T4) and triiodothyronine (T3). These thyroid hormones regulate everything from heart rate and body temperature to respiratory function and a woman’s menstrual cycle.

When the thyroid gland becomes underactive — from Hashimoto’s disease (an autoimmune disorder), iodine deficiency, or surgical removal of the thyroid gland, among other causes — an insufficient amount of thyroid hormone is produced, leading to a variety of symptoms that affect one or more organ systems and range in severity from mild to debilitating.

Symptoms of Hypothyroidism

In order to restore sufficient thyroid hormone levels in the body, everyone with hypothyroidism must take thyroid hormone replacement medication—exceptions include those whose underactive thyroid gland is transient (e.g., thyroiditis) or reversible (e.g., caused by a drug that can be discontinued).

There are four main goals of thyroid hormone replacement medication:

  • alleviate symptoms of hypothyroidism;
  • normalize the thyroid-stimulating hormone (TSH) level;
  • reduce the size of an enlarged thyroid (goiter) if present;
  • avoid overtreatment (becoming hyperthyroid);
  • taking hypothyroidism drugs properly.


Levothyroxine—also called l-thyroxine and L-T4—is a synthetic form of the T4 (thyroxine) hormone. T4 is the storage hormone, and it must be converted into T3, the active hormone, to be used by your cells.

Levothyroxine is the drug of choice for the treatment of hypothyroidism. In the United States, brand names are Synthroid, Levoxyl, Unithroid, and Tirosint.


Liothyronine is a synthetic form of T3 (triiodothyronine). Brand names of liothyronine in the United States are Cytomel and Triostat.

Due to the fact that experts, for the most part, recommend T4-monotherapy and not combination T4/T3 therapy for treating hypothyroidism, this medication is not commonly prescribed.

The T4/T3 Thyroid Drug Controversy

Research is ongoing about whether combination T4/T3 therapy may benefit a subgroup of people with hypothyroidism who have a certain genetic mutation. Keeping abreast of this research is valuable, as it may alter your thyroid care in the future.

Natural Desiccated Thyroid

Natural desiccated thyroid—also known as NDT, natural thyroid, or porcine thyroid,—is a prescription drug derived from the dried thyroid glands of pigs. NDT contains both T4 and T3.

Common brands are Armour Thyroid and Nature-thyroid, and a generic is also available.

Most endocrinologists and many mainstream physicians do not support or prescribe the use of natural desiccated thyroid drugs; this is because they are combination drugs and because the ratio of T4 to T3 does not match up to the ratio of T4 to T3 in humans.1 That said, certain select patients may respond well to NDT.

How Hypothyroidism Is Treated

Hyperthyroidism Medications

Hyperthyroidism means the thyroid gland is overactive, producing too much thyroid hormone. There are multiple causes of hyperthyroidism including Grave’s disease (another type of autoimmune disorder), noncancerous thyroid nodules, thyroid inflammation (thyroiditis), and a malfunctioning pituitary gland (which works in tandem with the thyroid gland).4 Moreover, a phase of Hashimoto’s disease can also cause hyperthyroidism in the same way that it causes hypothyroidism.

The treatment of hyperthyroidism is generally more complex than hypothyroidism, requiring one or more of the following treatments:

Anti-thyroid drug

  • radioactive iodine (RAI);
  • surgery to remove the gland (thyroidectomy).

The only “medications” for hyperthyroidism are anti-thyroid drugs. There are currently two approved for use in treating hyperthyroidism in the United States.

  • Tapazole (methimazole, or MMI);
  • Propylthiouracil (PTU);
  • Tapazole (methimazole).

The antithyroid drug Tapazole inhibits the thyroid from using iodine—usually from the diet—to produce thyroid hormone. It is a medication that is generally taken once a day by patients. Tapazole has fewer side effects and reverses hyperthyroidism more quickly than PTU, making it the preferred anti-thyroid drug choice.

Propylthiouracil (PTU)

PTU inhibits the thyroid gland from using iodine, thus slowing the overproduction of thyroid hormone. It also inhibits the conversion of the thyroid hormone T4 into T3. PTU has a short-acting timespan, so patients taking this medication usually are instructed to take the medication two to three times per day to effectively lower thyroid hormone levels.

PTU has more side effects than the other drugs discussed here. It is the preferred drug for hyperthyroidism only in a few situations—early pregnancy, severe thyroid storm, and in the event, a patient is experiencing serious side effects from methimazole.


Beta-blockers, like Inderal (propranolol), are not used to “treat” hyperthyroidism, but rather to reduce the symptoms of excess thyroid hormone on the body like a fast heart rate, tremor, and anxiety.

Three Ways to Treat an Overactive Thyroid

Thyroid Cancer Medications

The primary treatment for most thyroid cancers is surgery with removal of the entire thyroid gland (total thyroidectomy) or a lobe of the thyroid gland (lobectomy).

After surgery, patients will require thyroid hormone replacement medication (levothyroxine) to replace thyroid hormone production and suppress tumor regrowth.


Levothyroxine is used to treat hypothyroidism due to thyroid surgery for cancer just as it is used for other cases of underactive thyroid. Depending on the extent of the disease and the person’s risk for recurrent thyroid cancer, a doctor will determine what range TSH should be suppressed too and adjust the levothyroxine accordingly.

Suppression of the TSH is important for preventing cancer from returning.

Radioactive-Iodine Therapy

For large thyroid cancers, a thyroid cancer that has spread to the lymph nodes, and/or if you are considered high risk for recurrent cancer, radioiodine therapy may be given after surgery.

The radioactive iodine is given in a hospital setting in either liquid form or as a capsule. Its main goal is to kill off cancer cells that remain after surgery and destroy any remaining thyroid tissue.

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