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Taking daily pills of thyroid hormone (thyroid hormone
therapy) can serve 2 purposes:
- to help maintain the body's normal metabolism (by replacing
missing thyroid hormone)
- to help stop cancer cells from growing (by lowering TSH
levels)
After a thyroidectomy, the body is no longer able to make the
thyroid hormone it needs, so patients must take thyroid hormone pills
to replace the loss of the natural hormone.
Thyroid hormone may also help prevent some thyroid cancers
from returning. 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 cancer cells and lower the chance of having some thyroid
cancers (especially the high-risk cancers) come back.
Possible side effects
Even though these higher than normal levels of thyroid hormone
seem to have few side effects, some doctors have expressed concerns
about long-term issues, such as possible effects on the bones and
heart. Because of this, high doses of thyroid hormone may be reserved
for people with differentiated thyroid cancers who are at high risk of
recurrence.
Last Medical Review: 04/28/2009
Last Revised: 05/14/2009
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