Is Letrozole safe while breastfeeding?
Here is what LactMed, the Drugs and Lactation Database published by the U.S. National Institute of Child Health and Human Development (NICHD), reports about Letrozole. The text below is quoted from that source — it is not our own verdict.
Summary of use during breastfeeding
A minimal amount of information on letrozole excretion into milk indicates that the amounts might be of concern. Because of harm reported in animal studies, the manufacturer recommends that breastfeeding be discontinued during letrozole therapy and for 3 weeks after the last dose.
Effects on the breastfed infant
Relevant published information was not found as of the revision date.
Effects on milk supply
Relevant published information was not found as of the revision date.
Levels in milk
Maternal Levels. An abstract reported that a relative infant dose of 10.2% was found in nursing mother(s) taking letrozole, who provided 8 milk samples over 24 hours, but other details were not supplied.[1]
Infant Levels. Relevant published information was not found as of the revision date.
Letrozole in pregnancy
LactMed covers breastfeeding only. For what the NHS and the US prescribing label say about pregnancy, see:
“No published information” means the studies do not exist yet — not that Letrozole is known to be harmful, and not that it is known to be safe. Your prescriber or pharmacist can weigh your baby's age and whether a better-studied alternative would do the same job. Worth asking before stopping a medicine you need.
Source: Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Letrozole” (LM1344). LactMed on NCBI Bookshelf. LactMed is a registered trademark of the U.S. Department of Health and Human Services.
Educational summary of an authoritative source — not medical advice. Never start, stop, or change a medicine while breastfeeding without confirming with your doctor.