The short answer: Possibly, but only after a talk with your clinicians. The FDA-approved Mounjaro label was updated with a lactation study: after one 5 mg dose, tirzepatide was undetectable in 164 of 171 breast milk samples. The NIH LactMed database says a mother's need for tirzepatide is not a reason to stop breastfeeding. Still, there are no data on effects in nursing babies or on milk supply, so caution applies, most of all with newborns and preterm infants.
What does the Mounjaro label say about breastfeeding?
Section 8.2 (Lactation) of the Mounjaro prescribing information, revised in August 2026, has three main points:
- In a single-dose clinical lactation study, tirzepatide in breast milk was "either undetectable or low compared to the maternal administered dose."
- There are no available data on the effects of tirzepatide on the breastfed infant or on milk production.
- The benefits of breastfeeding should be weighed against the mother's clinical need for the drug and any possible effect on the baby.
The Zepbound label uses the same wording. That makes sense, since both brands contain the same drug, tirzepatide. Neither label says breastfeeding is forbidden. Neither says it is proven safe. The label leaves the decision to you and your prescriber.
Older articles often say "no human data exist." That is now out of date. The current labels include measured milk levels.
How much tirzepatide gets into breast milk?
The data come from a Lilly study registered as NCT05978713. It enrolled 11 healthy lactating women and finished in March 2024. Each woman got one 5 mg injection under the skin. Milk was then sampled for 28 days.
According to the label:
- 164 of 171 milk samples had no detectable tirzepatide. The test could detect levels down to 4 ng/mL.
- In the 7 samples with a measurable level, the total amount over 28 days was less than 0.02% of the mother's dose.
- The last measurable level showed up 5 days after the dose.
- The researchers could not calculate total milk exposure (AUC), because too few samples had measurable drug.
LactMed's August 2026 summary agrees: tirzepatide "is usually undetectable in breastmilk with subcutaneous doses of up to 5 mg."
Why is the baby's exposure thought to be low?
Two separate questions matter here. How much drug reaches the milk? And how much of that the baby absorbs?
The study above answers the first one. For the second, LactMed says absorption by the infant is unlikely. Its reason: tirzepatide is "probably partially destroyed in the infant's gastrointestinal tract and poorly absorbed orally."
The label's description and pharmacology sections helps explain why. Tirzepatide is a peptide, a chain of amino acids, with a molecular weight of 4,813.53 daltons. It is given by injection. The label reports 80% bioavailability after injection under the skin, but it gives no figure for oral use. The drug was designed to be injected, not swallowed. A baby who drinks the milk takes in any drug by mouth.
The drug also stays in the body a long time. The label gives a half-life of about 5 days, which is why Mounjaro is a once-weekly shot. If you want to know how the drug works, see our page on how tirzepatide works.
What do the data not tell us yet?
The study design has real limits. Knowing them helps you weigh the numbers.
- One dose only. Women got a single 5 mg shot. Mounjaro comes in doses from 2.5 mg up to 15 mg, given every week. The study did not test repeated weekly doses or higher doses.
- No babies were exposed. According to the trial record, women had to stop nursing before the dose and not resume during the study. So it measured milk, not infant effects.
- A narrow group. Women were at least 6 weeks postpartum, had term babies, and had no type 1 or type 2 diabetes.
- Milk supply was not studied. The label says there are no data on milk production.
This is why LactMed adds a caution. It says tirzepatide "should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant." It also notes that some experts recommend monitoring the baby's growth and milestones. Some also suggest checking the nursing mother's own nutrition.
Reviews agree the evidence is thin. A 2025 pharmacy review says data on these drugs in pregnancy and lactation "remain limited." A 2026 review on obesity care in women says that during lactation, "medication safety for the individual agent" comes before drug-based weight loss.
Does the birth control warning matter while you nurse?
Yes, if you use a pill. Tirzepatide slows stomach emptying. The label (section 8.3) says this may make oral hormonal birth control less effective. It advises switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase.
MedlinePlus gives the same advice in plain terms. Many nursing mothers use a pill, so this point is easy to miss. Our full guide to Mounjaro and birth control covers the details.
A new pregnancy also matters. The Zepbound label says weight loss offers no benefit during pregnancy and may harm the fetus. It advises stopping Zepbound once a pregnancy is recognized.
What should you ask before you start or restart?
Talk with both your obstetric clinician and your baby's pediatrician. Useful questions include:
- How old is my baby, and was my baby born preterm? LactMed's caution is strongest for newborns and preterm infants.
- Why do I need the drug now? Blood sugar control in type 2 diabetes is a different need than postpartum weight loss.
- Could I wait until my baby is older, or until weaning?
- How will we watch my baby's feeding, weight gain, and milestones?
- How will we check my milk supply and my own nutrition while my appetite is lower?
- Which birth control method fits with this drug?
If weight is the main goal, other first steps exist. The 2026 women's obesity review puts appropriate weight trajectories ahead of drug-based weight loss during lactation. Our Mounjaro diet plan covers food choices that also help when you are not on the drug. If you are comparing drugs, ozempic.md covers semaglutide, a related GLP-1 medicine.
Also tell your clinician about side effects like nausea, vomiting, or poor appetite. These can affect how well you eat and drink while nursing.
The bottom line
The newest Mounjaro and Zepbound labels report that one 5 mg dose left tirzepatide undetectable in almost all breast milk samples. LactMed says a mother who needs the drug does not have to stop breastfeeding. LactMed also says the baby likely absorbs little by mouth. But no study has looked at nursing babies, milk supply, repeated doses, or higher doses. Make the choice with your obstetric and pediatric clinicians, and take extra care with a newborn or preterm baby.
Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your obstetric clinician and your baby's pediatrician before you take tirzepatide while breastfeeding.