Concerns about antithyroid drugs center on the risk of thyroid suppression and goiter in the nursing infant, and cite concerns over potential nonthyroid side effects of antithyroid drugs, for example, autoimmune disturbances.
As far as safety, a number of studies have found no alteration in thyroid function, or effects on thyroid function and physical and intellectual development in infants who are breastfed by mothers treated with daily doses of PTU, ranging from 50 to 300 mg, methimazole at doses of 5 to 20 mg, and carbimazole at doses of 5 to 15 mg) for as long as eight months. Because methimazole (Tapazole) and carbimazole cross into milk more readily, and only trace amounts of PTU cross into breast milk, PTU is considered preferable and safer for use by a nursing mother with hyperthyroidism.
Generally, however, if a woman is taking any antithyroid medication while breastfeeding, regular monitoring of the breastfeeding infant's thyroid function is recommended. The drug should also be taken by the mother after a feeding.
Doctors are conflicted, however, about breastfeeding for women who are being treated for hyperthyroidism, even with PTU. These studies showing the effects of these drugs on breastfeeding infants have been small, so no medical experts have said that any antithyroid drug is 100% safe for use while breastfeeding. In fact, despite the studies that have shown PTU to be safe at certain dosages, a substantial number of doctors still caution against using these drugs while breastfeeding, and many drug information inserts report that postpartum patients receiving antithyroid drugs should not nurse their babies. A July, 2000 study in the journal Pediatrics found that more than one-third of pediatricians and endocrinologists still advise against breastfeeding for those mothers taking PTU, despite journal research claiming it is safe.
Ultimately, the decision to breastfeed while taking antithyroid medications is one a woman should make in conjunction with her own healthcare provider, and her infant's pediatrician.
Read more Frequently Asked Questions About Breastfeeding and Thyroid Disease
