Metformin Safety During Breastfeeding
Metformin is safe for use during breastfeeding, with multiple major medical societies—including the American College of Obstetricians and Gynecologists and the American Academy of Dermatology—explicitly recommending it as compatible with lactation, particularly for patients with type 2 diabetes, gestational diabetes, or polycystic ovary syndrome. 1
Guideline Consensus
- The American College of Obstetricians and Gynecologists recommends that metformin can be continued during breastfeeding for patients with type 2 diabetes. 1
- The American Academy of Dermatology classifies metformin as safe during breastfeeding and considers it a first-line choice for breastfeeding patients requiring pharmacologic therapy for metabolic conditions. 1
- The Fifth International Workshop-Conference on Gestational Diabetes states that limited data suggest metformin does not appear to have harmful neonatal effects. 1
FDA Drug Label Information
- The FDA label acknowledges that metformin is present in human milk, with infant doses approximately 0.11% to 1% of the maternal weight-adjusted dosage and a milk/plasma ratio ranging between 0.13 and 1. 2
- The FDA recommends that the developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for metformin and any potential adverse effects on the breastfed child. 2
Supporting Research Evidence
- Research demonstrates that metformin is excreted into breast milk at very low concentrations, with mean infant exposure of only 0.28-0.65% of the weight-normalized maternal dose—well below the 10% threshold of concern for breastfeeding safety. 3, 4
- No adverse effects on blood glucose have been measured in nursing infants exposed to metformin through breast milk. 3, 5
- Metformin is generally preferred along with insulin and second-generation sulfonylureas for treating diabetes mellitus during breastfeeding. 6
Important Safety Caveats
- Temporarily discontinue metformin during acute illness, dehydration, or administration of iodinated contrast to avoid lactic acidosis. 1
- Monitor maternal vitamin B12 levels with long-term metformin use, as deficiency can occur and potentially affect milk quality. 1
- Metformin may restore ovulation in anovulatory women, increasing pregnancy risk—discuss contraception needs with all premenopausal breastfeeding patients starting metformin. 1, 2
Clinical Bottom Line
Metformin presents minimal risk to breastfed infants due to low milk concentrations and negligible infant exposure relative to maternal dosing. The medication should not be withheld from breastfeeding mothers who require it for diabetes management or other metabolic conditions. 1, 2, 4