This guide sets out what the SmPC says about Mounjaro and fertility, why contraception is important during treatment, and the rules on planning a pregnancy. It draws on the UK Summary of Product Characteristics and the NHS. It is general information, and any decision about pregnancy or contraception while on Mounjaro should be discussed with your prescriber.
Does Mounjaro affect fertility?
The honest answer is that the effect of tirzepatide on fertility in humans is not known1. The SmPC states this directly, and notes that animal studies did not indicate direct harmful effects with respect to fertility 1. So there is no established evidence that Mounjaro harms fertility, but nor is there evidence confirming it is neutral in humans.
Because of that uncertainty, this guide does not make claims either way about Mounjaro improving or reducing fertility 1. The practical and well-defined parts of the picture are about contraception and pregnancy, which the SmPC and NHS are clear on, and which matter most day to day 23.
So if your question is whether Mounjaro will help or harm your chances of conceiving, the accurate position is that the human effect is unknown 1. What is clear, and important, is how to manage contraception and pregnancy planning safely, which the rest of this guide covers.
What the SmPC says about fertility
The SmPC's fertility statement is brief and worth quoting in substance: the effect of tirzepatide on human fertility is unknown, and animal studies with tirzepatide did not indicate direct harmful effects with respect to fertility 1. That is the extent of the specific fertility evidence in the licence.
It is important not to over-read this in either direction. The absence of harm in animal studies is reassuring but not the same as proof of safety for human fertility, and the unknown human effect is a statement of limited data rather than a warning of harm 1. This is an area where honesty about uncertainty is the right approach.
The more defined parts of the SmPC, contraception, pregnancy and breastfeeding, are where the clear guidance lies, and they are the practical focus for anyone thinking about fertility while on the medicine 23.
It is also worth being clear about what this guide deliberately does not do. It does not claim that Mounjaro boosts fertility, even though weight loss is sometimes discussed in that context, because the SmPC does not support such a claim and the human fertility effect is unknown 1. Equally, it does not suggest the medicine harms fertility, since the animal data showed no direct harm 1. Holding that honest uncertainty, while acting firmly on the clear contraception and pregnancy rules, is the right approach 12.
Contraception while on Mounjaro
This is the most important practical point. Tirzepatide can reduce the absorption of the oral contraceptive pill, particularly through its effect on stomach emptying, so the SmPC advises adding a barrier method or switching to a non-oral contraceptive for four weeks when you start treatment and for four weeks after each dose increase 2. The NHS gives the same advice 3.
This matters because reduced contraceptive effectiveness could lead to an unintended pregnancy, which is significant given the medicine must not be used in pregnancy 23. If there is any chance you could become pregnant, reliable contraception while on Mounjaro is essential, and the pill alone may not be sufficient during the windows above 2.
If you use the contraceptive pill, this is exactly the kind of thing to raise with your prescriber or pharmacist when starting Mounjaro or increasing the dose, so you can put a barrier or non-oral method in place for the relevant four-week periods 23.
There is also an indirect link worth knowing. Vomiting, which can happen as a gut side effect, can itself reduce the effectiveness of the oral contraceptive pill, separate from the absorption effect, so a bout of significant vomiting is another reason a backup method matters 23. The practical message is simple: while on Mounjaro, do not rely on the pill alone if there is any chance you could become pregnant, particularly at the start, after a dose increase, or during a spell of vomiting 23.
Considering treatment for weight management? You can start an assessment with a Cloud Pharmacy clinician, who will review your medical history and confirm whether treatment is appropriate.
Planning a pregnancy
If you want to become pregnant, the SmPC is clear: tirzepatide should be discontinued at least one month before a planned pregnancy, because it stays in the body a long time, with a half-life of around five days 1. The NHS puts the practical version at stopping at least four weeks before you start trying 3.
So planning a pregnancy on Mounjaro means planning to stop it in advance, with that one-month lead time built in 13. This is a decision to make with your prescriber, who can advise on stopping and on timing, rather than stopping abruptly on your own 3.
If you are weighing up treatment and know you may want to conceive in the near future, that is worth raising at the outset, so the plan fits around your pregnancy intentions from the start 13.
The one-month lead time exists because of the medicine's long half-life of around five days, meaning it takes time to clear from the body after the last dose 1. So planning a pregnancy on Mounjaro is less about a sudden stop and more about timing the last dose well ahead of trying to conceive, which your prescriber can help you work out 13. Building that lead time in is the safe way to move from treatment towards trying for a baby 1.
Pregnancy and breastfeeding
Mounjaro must not be used during pregnancy, and is not recommended in women of childbearing potential who are not using contraception 1. The NHS states it is not used in pregnancy as there is not enough information to say it is safe for the baby 3. If you become pregnant while taking it, tell your doctor 3.
On breastfeeding, the position has nuance: the SmPC notes that in a study the amount of tirzepatide in breast milk was undetectable to very low and, as a peptide, any small amount would be expected to be broken down rather than absorbed by the infant, so it could be considered during breastfeeding 1. The NHS, more cautiously, says it is not used while breastfeeding as it is not known whether it passes into breast milk 3. This is a decision to make with your prescriber based on your circumstances 3.
Either way, breastfeeding and pregnancy are situations to discuss individually with a clinician rather than decide from general information, given the differing emphases and the importance of getting it right 13.
The practical thread through all of this is that pregnancy and Mounjaro do not mix, so the emphasis is on preventing an unintended pregnancy during treatment and on stopping in good time before a planned one 12. That is why the contraception advice and the one-month stopping lead time matter so much, and why this is a conversation to have early with your prescriber if conceiving is anywhere in your thinking 23.
What to discuss with your prescriber
If fertility, contraception or pregnancy is relevant to you, raise it with your prescriber before starting Mounjaro and whenever your dose changes 2. The key things to cover are your contraception (and the four-week barrier or non-oral cover at the start and after each increase), any plans to conceive, and the need to stop at least a month before trying 123.
If you become pregnant unexpectedly while taking it, tell your doctor promptly, since the medicine is not used in pregnancy 3. And if you are breastfeeding or planning to, discuss the differing SmPC and NHS positions with your prescriber to decide what is right for you 13.
These are exactly the questions a clinical assessment is for, which is one reason Mounjaro is prescription-only and supplied after individual assessment 3. Our complete Mounjaro guide covers the wider picture.
If there is one thing to take from this guide, it is that the uncertainty about fertility itself should not be confused with the clarity around contraception and pregnancy 1. The human fertility effect being unknown is a reason for honesty, not alarm, while the rules on using reliable contraception during treatment and stopping at least a month before trying to conceive are firm and worth following closely 123. Treating those practical rules as the settled, important part, and discussing anything specific to your situation with your prescriber, is the safe and sensible approach 23.
Frequently asked questions
Does Mounjaro affect fertility?
The effect on human fertility is not known, and animal studies showed no direct harmful effect on fertility, so there is no established evidence either way 1. This guide does not claim it improves or reduces fertility. The clear, important practical points are about contraception during treatment and stopping before a planned pregnancy 21.Do I need extra contraception on Mounjaro?
If you use the contraceptive pill, yes during certain windows. Tirzepatide can reduce the pill's absorption, so the SmPC and NHS advise adding a barrier method or switching to a non-oral method for four weeks when you start and for four weeks after each dose increase 23. Reliable contraception matters because the medicine must not be used in pregnancy 1.Can I take Mounjaro while trying to get pregnant?
No. The SmPC advises stopping tirzepatide at least one month before a planned pregnancy, because it stays in the body a long time, and the NHS says at least four weeks before you start trying 13. It must not be used in pregnancy 1. Plan stopping with your prescriber rather than abruptly 3.Is Mounjaro safe in pregnancy?
No. Mounjaro must not be used during pregnancy, and the NHS says it is not used as there is not enough information to say it is safe for the baby 13. If you become pregnant while taking it, tell your doctor 3. It is also not recommended in women of childbearing potential who are not using contraception 1.Can I breastfeed while taking Mounjaro?
The positions differ slightly. The SmPC notes the amount in breast milk was undetectable to very low and could be considered during breastfeeding, while the NHS more cautiously says it is not used while breastfeeding as it is not known whether it passes into milk 13. This is a decision to make individually with your prescriber 3.Why do I need extra contraception when I start or increase Mounjaro?
Because tirzepatide can reduce the absorption of the contraceptive pill, especially through its effect on stomach emptying, the SmPC advises a barrier or non-oral method for four weeks at the start and after each dose increase 23. Vomiting as a side effect can also reduce the pill's effectiveness 2. This matters because the medicine must not be used in pregnancy 1.Your next step
The effect of Mounjaro on human fertility is not known, with animal studies showing no direct harm, so the honest position is one of uncertainty rather than a claim either way. What is clear and important is contraception: tirzepatide can reduce the pill's absorption, so a barrier or non-oral method is advised for four weeks at the start and after each dose increase, and the medicine must not be used in pregnancy.
If fertility, contraception or pregnancy is relevant to you, discuss it with your prescriber before starting and whenever your dose changes, plan to stop at least a month before trying to conceive, and tell your doctor promptly if you become pregnant. Breastfeeding is a decision to make individually with a clinician.
Disclaimer
This guide is for general information only and does not constitute medical advice, diagnosis or treatment. The information here describes general clinical context based on UK regulatory sources cited above; it is not a recommendation for any specific medicine or treatment, which can only be made by a prescriber following individual assessment.
If you are considering treatment, speak to your GP or pharmacist, or arrange a consultation with a Cloud Pharmacy clinician. Prescription-only medicines are issued only after clinical assessment and where appropriate.
If you experience side effects from any medicine, you can report them through the Yellow Card scheme at yellowcard.mhra.gov.uk.
