Is Lysine 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 Lysine. The text below is quoted from that source — it is not our own verdict.
Summary of use during breastfeeding
Lysine is an indispensable (essential) amino acid that is normally present in breastmilk. The recommended dietary allowance for nursing mothers for lysine is 52 mg/kg daily or 3.6 grams daily for a 70 kg person.[1] No information is available on the use of high-dose lysine supplementation during breastfeeding, such as for Herpes infection. There is no correlation between dietary intake of lysine and milk lysine content,[2] so oral lysine supplementation might not markedy increase the amount of lysine in milk. Caution is warranted in using any single amino acid at a level significantly above that normally found in food,[1] but lysine supplements are probably a low risk during breastfeeding. An alternate drug may be preferred while nursing a newborn or preterm infant.
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
The dietary reference intake (DRI) for infants up to 6 months of age is 640 mg or 107 mg/kg daily of lysine.[1]
Maternal Levels. The total lysine content of milk averages 915 mg/L in the first month postpartum and decreases to an average of 622 mg/L in month 6 postpartum.[3] Mature milk is considered to contain an average of about 755 mg/L of lysine.[4] No information is available on levels after the use of lysine supplements.
Infant Levels. Relevant published information was not found as of the revision date.
Alternatives LactMed lists
“No published information” means the studies do not exist yet — not that Lysine 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 “Lysine” (lysine). 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.