Thyroid Hormone Therapy

If your thyroid has been removed (thyroidectomy), your body can no longer make the thyroid hormone it needs. You will need to take thyroid hormone (levothyroxine) pills to replace the natural hormone and help maintain normal metabolism and possibly lower your risk of the cancer coming back.

Normal thyroid function is regulated by the pituitary gland. The pituitary makes a hormone called TSH that causes the thyroid gland to make thyroid hormone for the body. TSH also promotes growth of the thyroid gland and probably of thyroid cancer cells. The level of TSH, in turn, is regulated by how much thyroid hormone is in the blood. If the level of thyroid hormone is low, the pituitary makes more TSH. If the level of thyroid hormone is high, not as much TSH is needed, so the pituitary makes less of it.

Doctors have learned that by giving higher than normal doses of thyroid hormone, TSH levels can be kept very low. This may slow the growth of any remaining cancer cells and lower the chance of some thyroid cancers (especially high-risk cancers) coming back.

Possible side effects

Taking higher than normal levels of thyroid hormone seems to have few short-term side effects, but some doctors have expressed concerns about taking them for long periods of time. High levels of thyroid hormone can lead to problems with a rapid or irregular heartbeat. Over the long run, high doses of thyroid hormone can also lead to weak bones (osteoporosis). Because of this, doctors might avoid giving high doses of thyroid hormone unless you have a differentiated thyroid cancer and are at high risk of recurrence.