Can you take liothyronine while breastfeeding?
What LactMed says
The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.
Liothyronine (T3) is a normal component of human milk. If replacement doses of liothyronine are required by the mother, it is not a reason to discontinue breastfeeding. The American Thyroid Association recommends that subclinical and overt hypothyroidism should be treated with levothyroxine in lactating women seeking to breastfeed. Liothyronine dosage requirement may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.
Quoted from Liothyronine — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised June 15, 2026.
What LactMed would consider instead
LactMed ends this record by naming the drugs it would consider in place of liothyronine. Whether any of them fits depends on what you are treating — this is the database’s list, not a recommendation from us.
How much liothyronine gets into breastmilk
Milk levels of liothyronine have not been measured after exogenous administration of T3 in humans. Although somewhat controversial, liothyronine, unlike levothyroxine (T4), might pass into milk in amounts that affect infant thyroid status.
In a study of a new analytic technique, concentrations of several thyroid hormones were measured in 30 milk samples. The mean levothyroxine (T4) concentration was 94 mcg/L (range 48 to 194 mcg/L) and the mean dextrothyroxine concentration was 135 mcg/L (range 115 to 158 mcg/L). The mean liothyronine (T3) concentration was 52 mcg/L (range 32 to 109 mcg/L) and the mean reverse T3 concentration was 65 mcg/L (range 21 to 180 mcg/L). Among the 30 samples, the dextrothyroxine concentration was always higher than the levothyroxine concentration, and the reverse T3 concentration was always higher than the liothyronine concentration. The levels of levothyroxine were also higher than liothyronine levels. Several other thyroid hormones such as thyroxine; monoiodothyronine; 3,3 and 3,5-diiodothyronine were also measured.
Maternal Levels. In a study of 56 mothers with thyroid disorders, 50 had hypothyroidism and were being treated with levothyroxine; 5 mothers had controlled hyperthyroidism with no medications and 1 had hyperthyroidism treated with a medication. Milk levels of thyroid hormones were free T4 4.5 ng/L, total T4 29.6 mcg/L, free T3 2.3 ng/L and total T3 0.35 mcg/L. The average milk to serum level ratios over the period were free T4 0.32, total T4 0.3, free T3 0.78 and total T3 0.26. Levels of free and total T3 and total T4 in milk were positively correlated with their respective plasma levels.
Infant Levels. Relevant published information was not found as of the revision date.
What has been seen in breastfed infants
Relevant published information was not found as of the revision date. However, the thyroid hormone content of human milk from the mothers of very preterm infants appears not to be sufficient to affect the infant’s thyroid status.
Effects on milk supply
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.
Frequently asked questions
Can you take liothyronine while breastfeeding?
Liothyronine (T3) is a normal component of human milk. The full record is quoted on this page, and the decision is one to make with the person who prescribed it — LactMed itself states it is not a substitute for professional judgement.
What can I take instead of liothyronine while breastfeeding?
LactMed lists Levothyroxine as alternate drugs to consider. That is the database's own list for this drug — whether any of them suits you depends on what you are treating.
Does liothyronine pass into breastmilk?
LactMed's measured drug levels for liothyronine are quoted in full on this page, under "How much gets into breastmilk".
Do I need to pump and dump after taking liothyronine?
LactMed does not frame its records that way — it reports measured drug levels in milk and what has been observed in breastfed infants, which is what this page quotes. "Pump and dump" advice for a specific drug and dose should come from your clinician or a pharmacist, not from a general rule.
More on liothyronine
LactMed states that the information it presents is not a substitute for professional judgement, and that you should consult your healthcare provider for breastfeeding advice related to your particular situation. Nothing on this page is medical advice.