Is Metformin (metformin) safe for use in lactating patients with diabetes?

From the Guidelines

Metformin is safe for use in lactating patients with diabetes, as there is evidence it is safe for use in breastfeeding. The amount of metformin that passes into breast milk is very small, with infants receiving less than 1% of the mother's weight-adjusted dose, which is unlikely to cause hypoglycemia or other adverse effects in the breastfed infant 1.

Key Points

• Mothers can continue their prescribed metformin regimen while breastfeeding, typically ranging from 500-2550 mg daily divided into two or three doses.
• No dosage adjustments are specifically required for lactation.
• The recommendation is based on metformin's poor oral bioavailability, limited transfer into breast milk, and lack of reported adverse effects in breastfed infants.
• For mothers with type 2 diabetes or gestational diabetes who require medication during lactation, metformin is often preferred over other oral antidiabetic agents due to its established safety profile.
• However, monitoring the infant for signs of gastrointestinal disturbances, although rare, is still advisable.

Considerations

• A recent study published in the Journal of the American Academy of Dermatology in 2025 suggests that metformin can be used in breastfeeding patients with hidradenitis suppurativa, further supporting its safety in lactation 1.
• An older study published in Diabetes Care in 2007 also suggests that metformin is safe for use in breastfeeding women, although it notes that larger studies are needed to demonstrate safety 1.
• However, the most recent and highest-quality evidence supports the use of metformin in lactating patients, making it a safe choice for mothers with diabetes who are breastfeeding.

From the FDA Drug Label

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 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.

The risk of Metformin for lactating patients is not well established due to insufficient information. However, it is known that metformin is present in human milk, resulting in infant doses approximately 0.11% to 1% of the maternal weight-adjusted dosage.

• 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.
• Caution is advised when using metformin in lactating patients, as the effects on the breastfed infant are not well understood 2 2.

From the Research

Risk of Metformin for Lactating Patients

The risk of metformin for lactating patients with diabetes is a topic of interest, with several studies investigating its safety and efficacy.

• The concentration of metformin in breast milk is generally low, with the mean infant exposure to metformin reported to be in the range of 0.28-1.08% of the weight-normalized maternal dose 3.
• No adverse effects on blood glucose of nursing infants have been reported, and metformin during lactation versus formula feeding appears to have no adverse effects on infants' growth, motor-social development, and intercurrent illness during the first 6 months of life 3.
• However, systematic studies have not yet been done assessing how hyperinsulinemia, polycystic ovary syndrome, and metformin may affect lactation 3.

Metformin Use in Lactating Patients with Diabetes

Metformin may be considered a safe option for lactating patients with diabetes, as it has been shown to be effective in regulating blood glucose levels and has a low risk of adverse effects on infants.

• A study comparing metformin to insulin in the treatment of gestational diabetes found that metformin was effective in regulating blood glucose levels and had a lower risk of hypoglycemia compared to insulin 4.
• Another study found that metformin was a suitable alternative to insulin for the treatment of overt diabetes and early A2 gestational diabetes in pregnancy, with fewer subjective episodes of hypoglycemia and lower reported glucose values < 60 mg/dL 5.
• A systematic review of the use of metformin compared to insulin for the management of gestational diabetes found that metformin was an effective alternative therapy to insulin, with moderate to high-quality evidence demonstrating its effectiveness and safety 6.

Key Findings

• Metformin is generally considered safe for use in lactating patients with diabetes, with low concentrations in breast milk and no reported adverse effects on infants.
• Metformin is effective in regulating blood glucose levels and has a lower risk of hypoglycemia compared to insulin.
• More research is needed to fully understand the effects of metformin on lactation and infant development, particularly in the long term 7.