Drug Levels and Effects:

Summary of Use during Lactation:

Liothyronine (T3) is a normal component ofhumanmilk. If replacement doses of liothyronine are required by the mother, it is not necessarily a reason to discontinue breastfeeding. However, because no information is available on the use of exogenous liothyronine during breastfeeding, an alternate drug may be preferred. Liothyronine 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. Liothyronine is a normal component ofhumanmilk. Although somewhat controversial, liothyronine, unlike levothyroxine (T4), 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:

Relevant published information was not found as of the revision date. However, the thyroid hormone content ofhumanmilk from the mothers of very preterm infants appears not to be sufficient to affect the infants thyroid status.[7]

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 of liothyronine would not be expected to further improve lactation.

Alternate Drugs to Consider:



1. Galofre JC, Haber RS, Mitchell AA et al. 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. 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

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Thyroid Hormones

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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