Is Levothyroxine Safe in Breastfeeding

I am a breastfeeding mother and i want to know if it is safe to use Levothyroxine? Is Levothyroxine safe for nursing mother and child? Does Levothyroxine extracts into breast milk? Does Levothyroxine has any long term or short term side effects on infants? Can Levothyroxine influence milk supply or can Levothyroxine decrease milk supply in lactating mothers?

It should be taken into account whenever screening test are done in neonates. No problems have been reported when the usual therapeutic substitutive dosage is used to keep the mother euthyroid. Follow-up thyroid function cautiously in the infant when a higher suppressive dosage is used. Under latter conditions, a lack of ejection reflex despite an appropriate milk production has been observed in animals. American Academy of Pediatrics: Maternal Medication Usually Compatible With Breastfeeding.

Levothyroxine (T4) is a normal component of human milk. Limited data on exogenous replacement doses of levothyroxine during breastfeeding indicate no adverse effects in infants. The American Thyroid Association recommends that subclinical and overt hypothyroidism should be treated with levothyroxine in lactating women seeking to breastfeed.[1] Levothyroxine dosage requirement may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.[2]

Effects of exogenous thyroid hormone administration to mothers on their infant have not been reported. One case of apparent mitigation of cretinism in hypothyroid infants by breastfeeding has been reported, but the amounts of thyroid hormones in milk are not optimal,[10] and this result has been disputed.[11] The thyroid hormone content of human milk from the mothers of very preterm infants appears not to be sufficient to affect the infants' thyroid status.[12] The amounts of thyroid hormones in milk are apparently not sufficient to interfere with diagnosis of hypothyroidism.[13] In a telephone follow-up study, 5 nursing mothers reported taking levothyroxine (dosage unspecified). The mothers reported no adverse reactions in their infants.[14] One mother with who had undergone a thyroidectomy was taking levothyroxine 100 mcg daily as well as calcium carbonate and calcitriol. Her breastfed infant was reportedly "thriving" at 3 months of age.[15] A woman with propionic acidemia took levothyroxine 50 mcg daily as well as biotin, carnitine, and various amino acids while exclusively breastfeeding her infant for 2 months and nonexclusively for 10 months. At that time, the infant had normal growth and development.[16]

Adequate thyroid hormone serum levels are required for normal lactation. Replacing deficient thyroid levels should improve milk production caused by hypothyroidism. Supraphysiologic doses would not be expected to further improve lactation.