Antithyroid drugs: to breast-feed or not to breast-feed

Historically, women taking antithyroid drugs generally have not been permitted to breast-feed. However, recent studies suggest that infants exposed to the small amounts of antithyroid drugs in breast milk experience no change in thyroid function. Propylthiouracil is the drug of choice in this situation, since it does not cross membranes readily, and milk concentrations are therefore quite low. However, methimazole in low dosages might be used if the infant's thyroid status was monitored at frequent intervals.