Is metformin (biguanide oral hypoglycemic) safe to use during breastfeeding?

Metformin Safety During Breastfeeding

Metformin is safe to use during breastfeeding, with minimal transfer into breast milk and no reported adverse effects in breastfed infants. 1, 2, 3

Evidence on Metformin in Breast Milk

Transfer into Breast Milk

• Metformin is excreted into breast milk but in very low concentrations
• The milk-to-plasma ratio averages 0.35 (95% CI 0.2-0.5) 4
• Infant exposure is minimal, with mean relative infant dose of only 0.28% (0.16-0.4%) of the weight-normalized maternal dose 4
• This is well below the 10% threshold level of concern for medications during breastfeeding 4

Safety Data

• The FDA drug label confirms that metformin is present in human milk but at insufficient levels to cause adverse effects in breastfed infants 2
• The 2025 North American Clinical Practice Guidelines for Hidradenitis Suppurativa explicitly state that metformin is safe during breastfeeding 1
• A study of breastfeeding women taking metformin (median dose 1500 mg daily) found no health problems in their infants 4
• Metformin concentrations were very low or undetectable in infant plasma when measured 4

Clinical Recommendations

Preferred Agents for Diabetes During Lactation

• Metformin is considered a preferred agent for diabetes management during breastfeeding, along with insulin and second-generation sulfonylureas 3
• The American Academy of Dermatology specifically recommends metformin as safe for breastfeeding patients with hidradenitis suppurativa 1

Benefits for Specific Populations

• Particularly beneficial for breastfeeding mothers with metabolic comorbidities 1
• Can be used for mild to moderate hidradenitis suppurativa or as combination therapy 1
• Valuable option for women with type 2 diabetes or gestational diabetes history during lactation 1

Important Considerations

Monitoring

• No special monitoring of the infant is required when the mother is taking metformin during breastfeeding
• Regular maternal monitoring should continue as per standard diabetes management protocols

Common Pitfalls to Avoid

1. Discontinuing effective treatment unnecessarily: Some healthcare providers may recommend stopping metformin during breastfeeding due to outdated information or excessive caution
2. Confusing pregnancy and lactation recommendations: While some medications contraindicated in pregnancy are also contraindicated during lactation, metformin is safe in both scenarios
3. Overlooking patient preferences: Metformin offers a convenient oral option that many patients prefer over injectable insulin during the already demanding postpartum period

Conclusion

The available evidence strongly supports the safety of metformin during breastfeeding. The minimal transfer into breast milk and absence of reported adverse effects in infants make it an appropriate choice for breastfeeding mothers who require this medication.