In lactating women, how do glucagon-like peptide‑1 (GLP‑1) receptor agonists affect breast‑milk composition?

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Last updated: March 16, 2026 • View editorial policy

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GLP-1 Receptor Agonists and Breast Milk Composition

There are no human data demonstrating that GLP-1 receptor agonists alter breast milk composition, and current evidence suggests these medications should not be used during lactation due to insufficient safety data. 1

Current Evidence on Breast Milk Transfer

Animal Studies

  • GLP-1 receptor agonists are excreted in animal breast milk, but human excretion data are completely absent from the available literature 2
  • Animal studies provide the only evidence of lactational transfer, which cannot be directly extrapolated to human lactation 2

Human Placental Transfer (Indirect Evidence)

  • Minimal placental transfer has been documented in limited human studies:
    • Exendin-4 showed no transport across the maternal-fetal placental interface in animal models 2
    • Exenatide demonstrated a fetal-to-maternal concentration ratio of ≤0.017 in ex vivo human placental perfusion (single placenta study) 2
    • Liraglutide showed no significant maternal-to-fetal transfer at 3.5 hours post-exposure in one human subject 2
  • GLP-1 receptors are expressed in human placenta, but their functional significance during lactation is unknown 1

Endogenous GLP-1 in Breast Milk

Natural Presence

  • Endogenous GLP-1 is naturally present in human breast milk and changes across a single feeding 3
  • GLP-1 concentration is higher in hindmilk than foremilk (P ≤ 0.05), suggesting physiological variation during feeding 3
  • Hindmilk GLP-1 levels correlate inversely with infant weight gain from birth to 6 months (r = -0.67, P = 0.034) 3

Other Appetite Hormones

  • Leptin and PYY are also present in breast milk, with leptin correlating with maternal adiposity (r = 0.65-0.85, P < 0.02) 3
  • These endogenous hormones may play a role in infant appetite and growth regulation 3

Clinical Recommendations for Lactation

Guideline-Based Approach

GLP-1 receptor agonists should be discontinued during breastfeeding because:

  • No human data exist on drug excretion into breast milk 1, 2
  • The 2025 Endocrine Society/European Society of Endocrinology joint guideline identifies lactation as a priority area requiring research but provides no safety assurance for use 1
  • Animal data showing breast milk excretion cannot establish human safety 2

Safe Alternatives for Diabetic Mothers

Breastfeeding women with diabetes should use established safe medications 4:

  • Metformin is compatible with breastfeeding: mean infant exposure is 0.28-1.08% of weight-normalized maternal dose, well below the safety threshold 4
  • Glyburide is undetectable in breast milk and causes no hypoglycemia in nursing infants 4
  • Insulin remains the preferred option and does not transfer into breast milk due to its large molecular size 5

Critical Knowledge Gaps

Research Priorities

The 2025 guidelines explicitly call for investigation of 1:

  • Lactational transfer and breast milk concentrations of all GLP-1 receptor agonists
  • Effects on breastfed infant growth, development, and metabolic outcomes
  • Impact on maternal milk production and composition
  • Establishment of pregnancy and lactation registries to capture real-world exposure data

Maternal Glycemia Effects (Separate Issue)

  • In mothers with type 1 diabetes, maternal glucose 90-120 minutes before breastfeeding correlates with breast milk glucose and fructose but not with lactose, protein, or fatty acids 6
  • Higher breast milk glucose and leptin are found in women with versus without type 1 diabetes 6
  • This reflects maternal glycemic control, not GLP-1 receptor agonist effects 6

Clinical Pitfalls to Avoid

  • Do not assume that minimal placental transfer predicts minimal breast milk transfer—these are distinct pharmacokinetic processes 2
  • Do not confuse endogenous GLP-1 in breast milk with exogenous GLP-1 receptor agonist transfer—the former is a natural component, the latter is unstudied 3
  • Do not continue GLP-1 receptor agonists postpartum in breastfeeding women when proven-safe alternatives (metformin, glyburide, insulin) are available 4, 1
  • Do not extrapolate safety from other protein-based biologics—each medication class requires specific lactation data 7, 5

References

4
Guideline

diabetes and pregnancy: an endocrine society clinical practice guideline.

The Journal of clinical endocrinology and metabolism, 2013

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