Can I take metformin while pregnant or breastfeeding?

8.1 Pregnancy Risk Summary Limited data with metformin hydrochloride in pregnant women are not sufficient to determine a drug-associated risk for major birth defects or miscarriage. Published studies with metformin use during pregnancy have not reported a clear association with metformin and major birth defect or miscarriage risk [see Data] . There are risks to the mother and fetus associated with poorly controlled diabetes mellitus in pregnancy [see Clinical Considerations] . No adverse developmental effects were observed when metformin was administered to pregnant Sprague Dawley rats and rabbits during the period of organogenesis at doses up to 2 and 5 times, respectively, a 2,550 mg clinical dose, based on body surface area [see Data] . The estimated background risk of major birth defects is 6 to 10% in women with pre-gestational diabetes mellitus with an HbA1C >7 and has been reported to be as high as 20 to 25% in women with a HbA1C >10. The estimated background risk of miscarriage for the indicated population is unknown.

Prescribing label, section “8.1 Pregnancy” (opening excerpt): METFORMIN HYDROCHLORIDE (oral), A-S Medication Solutions. Read the full section on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.

Data from well-conducted studies indicate that metformin levels in milk are low and infants would receive less than 0.5% of their mother’s weight-adjusted dosage. Milk metformin levels are relatively constant during maternal metformin use, so timing of breastfeeding with respect to the administration times is of little benefit. Although the dose in milk is low, metformin is sometimes detectable in low levels in the serum of breastfed infants. One sizeable prospective study found no adverse effects in breastfed infants. Metformin is sometimes used as a galactogogue in women with reduced milk supply, but there is no evidence that it is effective. Metformin should be used with caution while nursing newborn and premature infants and those with renal impairment.

“Summary of Use during Lactation”, LactMed record “Metformin” (LM173), quoted verbatim. Everything LactMed reports about Metformin while breastfeeding.

8.2 Lactation Risk Summary Limited published studies report that metformin is present in human milk [see Data] . However, there is insufficient information to determine the effects of metformin on the breastfed infant and no available information on the effects of metformin on milk production. Therefore, the developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for metformin hydrochloride and any potential adverse effects on the breastfed child from metformin hydrochloride or from the underlying maternal condition. Data Published clinical lactation studies report that metformin is present in human milk which resulted in infant doses approximately 0.11% to 1% of the maternal weight-adjusted dosage and a milk/plasma ratio ranging between 0.13 and 1. However, the studies were not designed to definitely establish the risk of use of metformin during lactation because of small sample size and limited adverse event data collected in infants.

Prescribing label, section “8.2 Lactation”: METFORMIN HYDROCHLORIDE (oral), A-S Medication Solutions. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.