What is thyroid hormone replacement therapy?

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 used to treat an underactive thyroid (hypothyroidism). This is a thyroid that secretes too little or no thyroid hormones. The most commonly prescribed thyroid hormone replacement is pure synthetic thyroxine (T4) called levothyroxine.

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)

• 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 sequential 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 to "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 (T3 and T4) 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 your healthcare provider.

• Take your thyroid medicine 30 to 60 minutes before breakfast on an empty stomach Separate your thyroid medicine by 4 hours from any calcium or iron medicines you may take. 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 with your healthcare provider before switching to another brand of medicine.

• Tell other healthcare providers of 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 your healthcare provider know if you become pregnant.

• Tell your healthcare provider if you have any new symptoms.

• Tell all healthcare providers of your thyroid condition and medicine dosage.