Mounjaro and Breastfeeding: What Has Changed in 2026?

What has changed?

The current UK Mounjaro Summary of Product Characteristics (SmPC), updated 8 September 2026, now includes human lactation data. In a study involving 11 breastfeeding women given a single 5 mg dose of tirzepatide, concentrations in breast milk were undetectable or very low (<10 ng/mL) compared with maternal plasma levels. Because tirzepatide is a peptide, any small amount reaching breast milk would also be expected to be broken down in the infant gastrointestinal tract rather than absorbed intact.

SmPC wording: “Overall, tirzepatide could be considered for use during breast-feeding.”

This is a meaningful change from the previous position, where breastfeeding was generally treated as a reason to avoid GLP-1 treatment.

Supporting evidence

LactMed, updated 15 August 2026, similarly reports that tirzepatide is usually undetectable in breast milk at doses up to 5 mg. In the manufacturer study, 164 of 171 milk samples contained no detectable tirzepatide. LactMed also considers clinically significant infant absorption unlikely because tirzepatide is expected to undergo degradation within the gastrointestinal tract and has poor oral bioavailability.

LactMed therefore states that if a mother requires tirzepatide, breastfeeding does not automatically need to be discontinued, although caution remains appropriate while further data accumulate, particularly in newborn or premature infants.

Important limitations

This update should not be interpreted as evidence that tirzepatide is proven completely safe during breastfeeding.

The principal manufacturer lactation study involved only 11 women.
Exposure was assessed following a single 5 mg dose, rather than long-term weekly treatment.
Long-term infant outcome data remain limited.
It is not yet known whether the reduction in maternal food intake associated with tirzepatide could affect the composition or nutritional content of breast milk. Therefore, breastfeeding should no longer necessarily be regarded as an automatic exclusion, but treatment should be assessed individually.

Pharmulous prescribing approach

Where a breastfeeding patient requests tirzepatide, prescribers should consider:

Age of the infant.
Whether the infant was born at term or prematurely.
Whether breastfeeding remains exclusive or the infant is established on solids.
Infant growth and development.
Maternal indication and expected clinical benefit.
Maternal nutritional intake and hydration.
Previous tirzepatide exposure and tolerability, where relevant.
Other medical conditions and medicines.
The patient's ability to maintain adequate protein, micronutrient and overall caloric intake while breastfeeding.

Extra caution: Exercise additional caution in those breastfeeding a newborn or preterm infant, where both LactMed and the limited evidence base support a more conservative approach.

If treatment is agreed, the patient should be advised to continue routine monitoring of the infant's feeding, weight gain, growth and development. Maternal nutritional intake, hydration and milk supply should also be considered during follow-up.

Standard licensed tirzepatide dosing should still be followed; the lactation update does not introduce a separate dosing schedule for breastfeeding women.

Important discrepancy with existing MHRA public guidance

The MHRA's general GLP-1 patient guidance, last updated in February 2026, still states that GLP-medicines should not be taken while breastfeeding. This general webpage predates the update to the tirzepatide-specific SmPC and has not yet been revised to reflect the newer Mounjaro lactation wording.

Until broader national guidance is updated, tirzepatide use during breastfeeding should remain a documented, individual benefit-risk decision by the prescriber rather than routine prescribing.

This update is specific to tirzepatide and should not automatically be extrapolated to semaglutide, orforglipron or other GLP-1/incretin medicines, which have their own product information and evidence bases.