Mounjaro and Breastfeeding: Latest MHRA Guidance Explained

Mounjaro and breastfeeding is an important consideration for women managing type 2 diabetes while nursing. Following an update to its Summary of Product Characteristics (SmPC) in April 2026, the MHRA now indicates that Mounjaro (tirzepatide) could be considered for use during breastfeeding — a notable shift from earlier caution. This change is based on new evidence showing that tirzepatide passes into breast milk in only very small amounts. However, the decision remains individual and should be made with your GP or diabetes specialist, carefully weighing your treatment needs against your baby's wellbeing.

Can You Take Mounjaro While Breastfeeding?

Updated MHRA guidance from April 2026 states that Mounjaro (tirzepatide) could be considered during breastfeeding, based on evidence that breast-milk concentrations are undetectable to very low. The decision should still be made individually with your GP or diabetes specialist.

Current MHRA guidance is that Mounjaro (tirzepatide) could be considered for use during breastfeeding. This follows an update to its Summary of Product Characteristics (SmPC) in April 2026, and is a change from earlier advice that had cautioned against use while nursing. It is not a blanket recommendation: the decision should still be made together with your GP or diabetes specialist, weighing your treatment needs against your baby's wellbeing.

Tirzepatide is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist, licensed in the UK for the treatment of type 2 diabetes mellitus.^[1][2] It is given as a once-weekly subcutaneous injection.

What changed is the evidence on whether tirzepatide passes into breast milk. In a study of 11 breastfeeding women, tirzepatide concentrations in breast milk were undetectable to very low (less than 10 ng/ml) after a single 5 mg dose, compared with levels in the blood. Because tirzepatide is a peptide (a chain of amino acids), any small amount that does reach breast milk is expected to be broken down in the infant's digestive system rather than absorbed intact. On this basis, the SmPC concludes that tirzepatide could be considered for use during breast-feeding.

If you are breastfeeding or planning to breastfeed, speak with your GP or diabetes specialist before starting or continuing Mounjaro so the decision reflects your individual circumstances. Your healthcare team can help you balance effective diabetes management with your baby's wellbeing.

How Mounjaro May Affect Breast Milk and Your Baby

Very little tirzepatide passes into breast milk, with concentrations undetectable to below 10 ng/ml in a study of 11 women. As a large peptide, it is expected to be broken down in the infant's gut rather than absorbed.

Recent data suggest that very little tirzepatide passes into breast milk. In the study of 11 women described above, breast-milk concentrations were undetectable to very low (less than 10 ng/ml) after a single 5 mg dose, compared with levels found in the blood.

Tirzepatide is given by subcutaneous injection once weekly and has a half-life of around five days. As a large peptide molecule, it is unlikely to be absorbed intact by a breastfed infant: the acidic environment of the baby's stomach is expected to break down the peptide structure. This is one of the reasons the regulator now considers tirzepatide compatible with breastfeeding.

The following remain theoretical, have not been reported in breastfed infants, and are considered unlikely given how little tirzepatide reaches breast milk:

• Gastrointestinal effects: tirzepatide commonly causes nausea, vomiting and diarrhoea in adults; similar effects in breastfed infants have not been documented.^[1][2]

• Hypoglycaemia: tirzepatide's glucose-lowering effect is glucose-dependent, which limits the risk of low blood sugar.

• Growth and development: the long-term effects of GIP/GLP-1 receptor agonist exposure during infancy have not been studied.

One genuine uncertainty noted in the SmPC is that it is not known whether the reduced food intake some people experience on tirzepatide could affect the composition or nutrient content of breast milk. This is worth discussing with your healthcare team, particularly if your appetite is noticeably reduced while on treatment.

Alternative Diabetes Treatments During Breastfeeding

Insulin therapy and metformin are well-established, compatible alternatives for managing type 2 diabetes while breastfeeding. Lifestyle measures including balanced nutrition and blood glucose monitoring also support safe diabetes management postpartum.

Mounjaro is one of several options for managing type 2 diabetes while breastfeeding, and it helps to understand the alternatives so you and your healthcare team can choose the most suitable approach. NICE guidance emphasises individualised treatment plans that consider both maternal health and infant safety.

Insulin therapy is well established during breastfeeding. All insulin formulations (rapid-acting, short-acting, intermediate-acting and long-acting analogues) are considered compatible, as insulin does not pass into breast milk in clinically significant amounts, and any present would be digested in the infant's gastrointestinal tract.^[11] Many women who used insulin during pregnancy continue it safely postpartum.

Metformin is also considered suitable during breastfeeding and is often a first-line oral medication for type 2 diabetes. It passes into breast milk only in small quantities (less than 1% of the maternal dose), with no adverse effects reported in breastfed infants.^[12][13] The British National Formulary (BNF) notes that metformin may be used while breastfeeding, with infant monitoring advisable.

Lifestyle measures support diabetes management and are fully compatible with breastfeeding:

• Balanced nutrition with regular meal timing

• Physical activity appropriate for the postpartum period

• Sustainable weight management

• Blood glucose monitoring to guide treatment adjustments

Other oral medications vary in the strength of breastfeeding evidence. Glibenclamide has limited data suggesting low milk transfer; other sulphonylureas and newer agents generally have less evidence and, if used, warrant caution and infant monitoring. Your diabetes specialist can review your circumstances and recommend the regimen that best balances glycaemic control with infant safety.

When to Discuss Mounjaro with Your Healthcare Provider

Speak with your GP or diabetes specialist before starting, continuing, or changing Mounjaro if you are breastfeeding, planning to breastfeed, or planning a pregnancy, to ensure decisions reflect current evidence and your individual circumstances.

It is worth speaking with your GP or diabetes specialist team before starting, changing or continuing Mounjaro when breastfeeding or family planning are involved, so decisions are made together and based on current evidence.

Contact your healthcare professional promptly if:

• You discover you are pregnant while taking Mounjaro, as the medication is not recommended during pregnancy and alternatives should be arranged

• You are breastfeeding, or planning to, and want to start or continue Mounjaro, so you can discuss the latest guidance together

• You are planning a pregnancy in the near future while using Mounjaro

Consider a routine appointment to discuss Mounjaro if:

• You are breastfeeding or plan to within the next year and are weighing up diabetes treatment options

• Your current diabetes medications are not achieving adequate control while you are nursing

• You have questions about how Mounjaro fits alongside breastfeeding

The SmPC notes that tirzepatide can reduce the body's exposure to oral hormonal contraceptives. If you take an oral contraceptive, you should use a barrier method (such as condoms) for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase, or switch to a non-oral method of contraception. This does not apply to non-oral contraceptives. Your healthcare professional can advise on the most suitable option, including methods appropriate during breastfeeding.

Your diabetes review might include discussion of:

• Your current glycaemic control and HbA1c levels

• How Mounjaro and any alternatives fit with breastfeeding

• Your breastfeeding plans and timeline

• The benefits and risks of each option

• Monitoring requirements for you and your baby

Never stop prescribed diabetes medication without medical guidance, as uncontrolled blood glucose carries significant health risks.

Safety Considerations for Nursing Mothers Taking Mounjaro

Nursing mothers taking Mounjaro should monitor their own nutrition and hydration, as tirzepatide can reduce appetite, and watch for any changes in their baby's feeding, weight gain, or gastrointestinal symptoms. Side effects can be reported via the MHRA Yellow Card scheme.

Where Mounjaro is used during breastfeeding, a few practical points are worth keeping in mind so that both your diabetes and your baby's needs are well managed.

Maternal considerations:

• Gastrointestinal effects: nausea, vomiting, diarrhoea and reduced appetite are common with tirzepatide. These can affect your nutrition and hydration, and the SmPC notes it is not known whether reduced food intake affects the composition or nutrient content of breast milk. Aim to maintain a balanced diet and adequate fluids, and raise any concerns with your healthcare team.

• Energy needs: breastfeeding increases your energy requirements, so it is worth being mindful of eating enough if tirzepatide reduces your appetite.

• Hypoglycaemia: tirzepatide alone carries a low risk of low blood sugar, but the risk rises when it is combined with insulin or a sulphonylurea. Episodes of hypoglycaemia could affect your ability to care for your baby, so discuss monitoring with your team.

Infant monitoring:

While very little tirzepatide is expected to reach breast milk, it is sensible to keep an eye on your baby's:

• Feeding patterns and weight gain

• Any gastrointestinal symptoms (unusual fussiness, vomiting, diarrhoea)

• General wellbeing and developmental milestones

Reporting side effects:

If you experience side effects, you can report them through the MHRA Yellow Card scheme (www.mhra.gov.uk/yellowcard). Reporting helps monitor the ongoing safety of medicines.

Making the decision:

Whether to use Mounjaro while breastfeeding is best decided with your healthcare professional, weighing the importance of good diabetes control against the current evidence, which indicates only minimal transfer into breast milk. Your team can help you reach a decision that protects both your health and your baby's wellbeing.

Scientific References

1. Mounjaro KwikPen 10 mg solution for injection in pre-filled pen – Summary of Product Characteristics.
2. Mounjaro KwikPen 2.5 mg solution for injection in pre-filled pen – Summary of Product Characteristics.
3. Mounjaro: INN – tirzepatide. EPAR Product Information.
4. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss.
5. Four-dose Mounjaro KwikPen approved by MHRA for diabetes and weight management.
6. Tirzepatide – BNF monograph.
7. Tirzepatide – BNF Interactions.
8. Tirzepatide for managing overweight and obesity (TA1026): Prescribing, reviewing and stopping tirzepatide.
9. GLP-1 medicines for weight loss and diabetes: what you need to know.
10. Metformin hydrochloride – BNF monograph.
11. Diabetes, pregnancy and breast-feeding – BNF treatment summary.
12. Pregnancy, breastfeeding and fertility while taking metformin.
13. Transfer of metformin into human milk.
14. Type 2 diabetes in adults: management (NG28) – Initial medicines.
15. Type 2 diabetes – BNF treatment summary.
16. A Comprehensive Review on the Pharmacokinetics and Drug-Drug Interactions of Approved GLP-1 Receptor Agonists and a Dual GLP-1/GIP Receptor Agonist. Drug Des Devel Ther. 2025.
17. When New Therapies Meet Old Challenges: Tirzepatide-Warfarin Interaction in A Mechanical Mitral Valve Patient. Eur J Case Rep Intern Med. 2024.
18. Lithium toxicity following a change from semaglutide to tirzepatide for weight loss management. Ment Health Clin. 2025.
19. The adverse effects associated with tirzepatide use in patients at increased risk of cardiovascular events: a systematic review with meta-analysis and Trial Sequential Analysis. BMC Med. 2025.

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