Mounjaro and pregnancy: planning, unexpected pregnancies and breastfeeding

In short

Do not use Mounjaro in pregnancy (SmPC section 4.6)
Stop at least 1 month before a planned pregnancy
If you become pregnant on Mounjaro, stop it and contact your GP or midwife straight away
Bumps reports data on about 47,000 pregnancies exposed to GLP-1 medicines, mostly early, with no clear signal of harm so far
UK guidance differs on breastfeeding, so speak to your doctor before using Mounjaro while you breastfeed

Do not use Mounjaro if you are pregnant. Stop it at least 1 month before you start trying for a baby, and keep using contraception until then. If you find out you are pregnant while taking it, stop the injections and contact your GP or midwife straight away. Reports so far from early pregnancy exposure do not raise concern about harm to the baby, but the evidence is still limited.

Why Mounjaro is not used in pregnancy

The SmPC says tirzepatide should not be used during pregnancy. The MHRA explains why: there are not enough safety data in humans, and some animal studies showed harm to the developing baby. Weight loss is not recommended during pregnancy in any case, and diabetes in pregnancy is treated with medicines which have more safety data.

The SmPC also says tirzepatide is not recommended for anyone able to become pregnant who is not using contraception.

Planning a pregnancy

How long to stop before trying

Stop Mounjaro at least 1 month before a planned pregnancy. The SmPC, the NHS and the MHRA all give this figure. Tirzepatide has a half-life of about 5 days, so a month allows the level in your body to fall close to zero.

Medicine	Stop at least this long before trying
Tirzepatide (Mounjaro)	1 month
Semaglutide (Wegovy, Ozempic)	2 months
Liraglutide	No gap needed, stop when you start trying

These figures come from the MHRA and the FSRH.

What to plan with your prescriber or GP

When to take your last dose, counting back at least a month from when you want to start trying
How to manage appetite and weight once you stop, as appetite usually returns within weeks
Folic acid, which the NHS advises taking before you conceive and for the first 12 weeks
A switch to other diabetes treatment, if you take Mounjaro for type 2 diabetes

If you have diabetes, speak to your diabetes team before you stop. They will plan a safe switch so your blood sugar stays under control.

If you find out you are pregnant on Mounjaro

Stop the injections and contact your GP or midwife straight away. The MHRA says to speak to a healthcare professional as soon as you think you might be pregnant. If you use Mounjaro for type 2 diabetes, speak to your doctor about changing your medicine rather than stopping all treatment.

Bumps, the UK service run by the UK Teratology Information Service, gives the most detailed UK view. Its leaflet updated in September 2026 says:

Studies include about 47,000 pregnancies exposed to GLP-1 medicines, most in early pregnancy before the person knew
The reports so far do not raise concern about harm to the baby, though more research is needed
Use later in pregnancy has not been well studied
Early exposure does not need extra scans for birth defects beyond the usual 20 week scan
You may be offered more regular monitoring if you have type 2 diabetes or a high BMI

For context, Bumps gives the background rates in all pregnancies as about 1 in 5 for miscarriage and about 1 in 40 for a major birth defect.

Tell your midwife the dose you were on and the date of your last injection. Report the pregnancy to the MHRA through the Yellow Card scheme, which helps build the safety picture.

Why unplanned pregnancies happen on weight loss medicines

Two things can raise the chance of an unexpected pregnancy.

First, Mounjaro can make the contraceptive pill less reliable. The SmPC and the FSRH advise condoms or a non-oral method for 4 weeks after starting and for 4 weeks after each dose increase. The contraceptive pill page explains the windows.

Second, losing weight can change your cycle. Periods which were irregular may become regular, and some people start ovulating more often. The SmPC says the effect of tirzepatide on human fertility is unknown, so no figure exists for how large this effect is. The periods page covers cycle changes.

Breastfeeding

UK sources do not fully agree here. The NHS and the MHRA say not to use tirzepatide while breastfeeding because there is not enough safety information. The latest UK patient leaflet says tirzepatide passes into breast milk in very low amounts and tells you to talk to your doctor before using or continuing it.

The practical step is the same either way. Do not start or restart Mounjaro while breastfeeding without your doctor agreeing first. When you do restart after your baby, your prescriber may start you again at a lower dose. The restarting guide explains why.

Eating enough matters while you breastfeed. The eating too little page lists the warning signs of an intake falling too low.

Partners taking Mounjaro

Bumps says there is no evidence a father's use of a GLP-1 medicine harms the baby through effects on sperm. The pregnancy and contraception precautions apply to the person able to become pregnant.

When to get help

Call 999 or go to A&E if you are pregnant or might be and have:

Sudden severe pain low in your tummy, often on one side, with bleeding, shoulder tip pain or feeling faint
Heavy bleeding from the vagina

Call 111 or see a GP today if:

You have a positive pregnancy test while taking Mounjaro
You are pregnant and vomiting so much you cannot keep fluids down
You had sex without contraception during a 4 week window on the pill and need emergency contraception

Mention at your next check if:

You plan to try for a baby in the next 6 months
You are breastfeeding and thinking about restarting
Your periods have changed since starting Mounjaro

Questions people ask

How long before trying to get pregnant should I stop Mounjaro?

At least 1 month. The SmPC, the NHS and the MHRA all give this figure for tirzepatide. Semaglutide medicines such as Wegovy need at least 2 months, because they leave the body more slowly. Keep using contraception until you have stopped for the full month.

I found out I am pregnant while taking Mounjaro. What should I do?

Stop taking it and contact your GP or midwife straight away. The UK pregnancy medicines service Bumps says most exposures happen before people know they are pregnant, and the reports so far do not raise concern about harm to the baby. You do not need extra scans for birth defects because of early use, but you may be offered closer monitoring if you have diabetes or a high BMI.

Can Mounjaro make you more fertile?

The SmPC says the effect of tirzepatide on human fertility is unknown. Weight loss can make periods more regular, and the medicine can make the contraceptive pill less reliable in the first weeks of each dose. Both can lead to an unplanned pregnancy, so use reliable contraception.

Can I take Mounjaro while breastfeeding?

The NHS and the MHRA say not to use it while breastfeeding. The latest UK leaflet says tirzepatide passes into breast milk in very low amounts and asks you to talk to your doctor first. Do not start or restart Mounjaro while breastfeeding without your doctor's agreement.

Does it matter if my partner takes Mounjaro?

Bumps says there is no evidence a father's use of a GLP-1 medicine harms the baby through effects on sperm. The precautions on this page apply to the person who could become pregnant.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Mounjaro and pregnancy: planning, unexpected pregnancies and breastfeeding. Site: Mounjaro Info (https://mounjaroinfo.co.uk/side-effects/mounjaro-and-pregnancy/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

Mounjaro should not be used during pregnancy because there is not enough safety information for the baby. The SmPC, the NHS and the MHRA advise stopping at least 1 month before trying to conceive, and anyone who finds out they are pregnant on it should stop and contact a healthcare professional straight away. UK pregnancy experts say reports so far from early exposure to GLP-1 medicines do not raise concern, but more research is needed.

Do not use Mounjaro in pregnancy (SmPC section 4.6)
Stop at least 1 month before a planned pregnancy
If you become pregnant on Mounjaro, stop it and contact your GP or midwife straight away
Bumps reports data on about 47,000 pregnancies exposed to GLP-1 medicines, mostly early, with no clear signal of harm so far
UK guidance differs on breastfeeding, so speak to your doctor before using Mounjaro while you breastfeed

Cite as: Mounjaro Info, "Mounjaro and pregnancy: planning, unexpected pregnancies and breastfeeding", https://mounjaroinfo.co.uk/side-effects/mounjaro-and-pregnancy/, reviewed 22 October 2026.