Does Mounjaro Impact Fertility — and What Should You Know Before Starting?

Is Mounjaro safe to use if you are trying to get pregnant?

No, and this is not a provisional caution. The prescribing guidance for tirzepatide is explicit: the medicine should not be used in pregnancy, during breastfeeding, or when you are actively trying to conceive. The MHRA advises that effective contraception should be used throughout treatment and for a wash-out period before attempting conception. If you are planning a pregnancy, you should discuss stopping Mounjaro with your prescriber well in advance, because the medicine needs adequate time to clear from your system.

The reason the data gap exists is straightforward: clinical trials running over 72 weeks excluded participants who were pregnant or planning pregnancy, which is standard practice for medicines of this type. That means we have no robust human trial evidence on whether tirzepatide affects the ability to conceive in the first place. Animal studies (referenced in the Summary of Product Characteristics available via the Mounjaro SmPC on the eMC) showed embryo-fetal toxicity at high doses, which is one reason the guidance is so clear. If you want to understand how tirzepatide is classified from a pregnancy-risk perspective, that page covers the regulatory position in more detail.

One practical note worth raising: if you store your pen in the fridge door alongside daily essentials, the routine can make it easy to take without thinking. If your circumstances change and you want to stop, tell your prescriber promptly rather than simply leaving a pen unused.

Could losing weight with Mounjaro actually improve fertility for some people?

Possibly, and this is where the picture gets more nuanced. Obesity is associated with hormonal disruption that can reduce fertility in both women and men. In women, excess adipose tissue affects oestrogen metabolism and can worsen conditions like PCOS, a leading cause of anovulatory infertility. In men, elevated BMI is linked to lower testosterone levels and reduced sperm quality. Weight reduction (by any effective means) is known to improve these markers.

The SURMOUNT-1 trial, published in the New England Journal of Medicine, demonstrated average body-weight reductions of around 20–21% at the 15mg dose over 72 weeks in adults with obesity. Reductions of that magnitude have historically been associated with improvements in menstrual regularity, androgen levels, and, in some women with PCOS, restored ovulation. Our page on Mounjaro's potential effects in men covers the male-specific evidence separately.

The important distinction is that any fertility-related benefit would be a downstream effect of weight loss, not a direct pharmacological action of tirzepatide on reproductive tissue. Mounjaro is licensed for weight management, nothing more. And crucially, if weight loss improves ovulatory function, a person may become pregnant more readily than they expected while still on the medicine, which is precisely why reliable contraception matters throughout treatment. The NHS England guidance on weight-management injections covers the contraception question in useful detail.

What is the contraceptive pill interaction that prescribers flag?

This is a question our prescribers hear regularly, and it deserves a clear answer. Tirzepatide slows gastric emptying, and this matters for oral contraceptives because slower gut transit can alter how consistently the pill is absorbed. For the first four weeks of Mounjaro treatment, and for four weeks following every dose increase, women using oral contraception should use an additional barrier method, condoms being the most practical option for most people.

There is currently no equivalent evidence of this interaction for injectable semaglutide (Wegovy), though the general MHRA advice to use contraception during GLP-1 treatment applies broadly. If you are on an oestrogen-containing patch or gel, the absorption concern does not apply in the same way; NHS England recommends considering transdermal HRT or contraception for women on tirzepatide, and your prescriber can advise on your specific situation. Our broader overview of Mounjaro and fertility considerations explores this area further, and you can also read about whether Mounjaro can support fertility outcomes in specific populations.

If you are using any hormonal contraceptive method, mention it explicitly during your consultation. A prescriber who has the full picture can make a much better-informed recommendation than one working from partial information.

Who should you speak to before making a decision?

Anyone weighing up whether to start, continue, or stop Mounjaro in the context of their fertility plans should have that conversation with a clinician who knows their full medical history. That means their GP, a reproductive medicine specialist, or a gynaecologist, not just an online pharmacy. A prescriber can help you think through timing, the wash-out period before trying to conceive, and whether your underlying conditions (PCOS, insulin resistance, obesity-related hormonal changes) are better addressed with or without continued treatment.

If you have questions about how Mounjaro may affect your fertility, that page sets out what the current evidence does and does not tell us, and our dedicated page on what effect Mounjaro can have on fertility goes further into the hormonal and reproductive mechanisms involved. What is certain is that these are prescription-only medicines, assessed individually by a registered prescriber, and that the clinical picture is genuinely individual. If you are curious about the broader treatment landscape, our weight-loss treatment overview explains the options available through a regulated UK clinical pathway. For anything touching fertility specifically, please bring your prescriber into the conversation early, not after you have already made a decision. You can check your eligibility and start a free consultation with our GPhC-registered prescribers, who review every application personally the same day it arrives.