Drug Levels and Effects:

Summary of Use during Lactation:

Liotrix is a mixture of levothyroxine (T4) and liothyronine (T3), which are normal components ofhumanmilk. Limited data on exogenous replacement doses of levothyroxine during breastfeeding indicate no adverse effects in infants. No information is available on the use of exogenous liothyronine during breastfeeding. If thyroid is required by the mother, it is not a reason to discontinue breastfeeding. Thyroid dosage requirement may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.[1]

Drug Levels:

Milk levels of thyroid hormones have not been measured after exogenous administration in humans. Levothyroxine is a normal component ofhumanmilk. Although somewhat controversial, it appears that levothyroxine passes into milk poorly and that liothyronine might pass into milk in amounts that affect infant thyroid status.[2][3][4][5][6]

Maternal Levels.

Relevant published information was not found as of the revision date.

Infant Levels.

Relevant published information was not found as of the revision date.

Effects in Breastfed Infants:

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,[7] and this result has been disputed.[8] The thyroid hormone content ofhumanmilk from the mothers of very preterm infants appears not to be sufficient to affect the infants' thyroid status.[9] The amounts of thyroid hormones in milk are apparently not sufficient to interfere with diagnosis of hypothyroidism.[10]

In a telephone follow-up study, 5 nursing mothers reported taking levothyroxine (dosage unspecified). The mothers reported no adverse reactions in their infants.[11]

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.[12]

Possible Effects on Lactation:

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.


1. Galofre JC, Haber RS, Mitchell AA, Pessah R, Davies TF. Increased postpartum thyroxine replacement in Hashimoto's thyroiditis. Thyroid. 2010;20:901-8. PMID:20615129
2. Sato T, Suzuki Y. Presence of triiodothyronine, no detectable thyroxine and reverse triiodothyronine inhumanmilk. Endocrinol Jpn. 1979;26:507-13. PMID:499092
3. Varma SK, Collins M, Row A et al. Thyroxine, tri-iodothyronine, and reverse tri-iodothyronine concentrations inhumanmilk. J Pediatr. 1978;93:803-6. PMID:712487
4. Mallol J, Obregon MJ, Morreale de Escobar GM. Analytical artifacts in radioimmunoassay of L-thyroxin inhumanmilk. Clin Chem. 1982;28:1277-82. PMID:7074933
5. Oberkotter LV, Tenore A. Separation and radioimmunoassay of T3 and T4 inhumanbreast milk. Horm Res. 1983;17:11-8. PMID:6551313
6. Koldovsky O. Hormones in milk. Vitam Horm. 1995;50:77-149. PMID:7709605
7. Bode HH, Vanjonack WJ, Crawford JD. Mitigation of cretinism by breast-feeding. Pediatrics. 1978;62:13-6. PMID:683777
8. Letarte J, Guyda H, Dussault JH et al. Lack of protective effect of breast-feeding in congenital hypothyroidism: report of 12 cases. Pediatrics. 1980;65:703-5. PMID:7367075
9. van Wassenaer AG, Stulp MR, Valianpour F et al. The quantity of thyroid hormone inhumanmilk is too low to influence plasma thyroid hormone levels in the very preterm infant. Clin Endocrinol. 2002;56:621-7. PMID:12030913
10. Abbassi V, Steinour A. Successful diagnosis of congenital hypothroidism in four breast- fed neonates. J Pediatr. 1980;97:259-61. PMID:7400893
11. Ito S, Blajchman A, Stephenson M et al. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993;168:1393-9. PMID:8498418
12. Caplan RH, Wickus GG. Reduced calcitriol requirements for treating hypoparathyroidism during lactation. A case report. J Reprod Med. 1993;38:914-8. PMID:8277494

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Thyroid Hormones

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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