Does Weight Loss Medication Affect Fertility? A UK Guide (October 2026)

01 · The core answer

The short answer: timing and contraception matter most

For anyone using Mounjaro, the fertility question is mostly about timing rather than a permanent effect. The prescribing information tells you to stop before trying for a baby, to avoid use in pregnancy, and to take care with contraception while you are on treatment.¹

That is deliberately cautious. You will find confident claims online in both directions, from reassurance that nothing can go wrong to warnings that weight loss drugs cause infertility. Neither claim is supported by the Mounjaro prescribing information.

02 · What to decide

The decisions you are actually facing

Most readers are in one of three positions, and the right next step differs for each.

• You are not trying to conceive now but might later. Plan the stop date with your prescriber well ahead. The label asks for treatment to stop at least one month before trying, so conception plans need a lead-in rather than a sudden decision.
• You are trying to conceive now. Tell your prescriber before starting. Mounjaro should be stopped at least one month before trying to conceive, so a conversation about timing is the safest first move.
• You could become pregnant by accident. Look at your contraception.

If you are weighing up whether treatment fits alongside fertility plans, our weight loss clinic page explains how a consultation works, and the free consultation is the right place to raise it. A GPhC-registered prescriber reviews every request, and fertility plans are exactly the sort of detail that should be on the record.

03 · The other side

Weight loss can help fertility for some people

Medication is only half of the story, because weight itself influences fertility. Mounjaro is not licensed specifically for PCOS, but many women with PCOS meet the licensed weight-management criteria, and weight loss is a first-line recommendation that can improve insulin resistance, cycles and symptoms.⁴ Improving weight can restore ovulation, which is why fertility plans belong in your consultation rather than being hidden from it.⁴

04 · Pregnancy and conception

Mounjaro, pregnancy and trying to conceive

Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive.¹ If you become pregnant during treatment, stop the medicine and tell your prescriber promptly.¹³ Those are the instructions, and they are the same whether the pregnancy was planned or not.

It tells you to build a gap into your plans. In practice that means deciding with your prescriber when to finish treatment, using reliable contraception until then, and only trying to conceive once the gap has passed.

The medicine takes time to leave the body. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ This is why the stop date matters: stopping is not an instant reset.

If a test shows you are pregnant, do not wait for a routine review. Stop the medicine and contact your prescriber promptly. Report any concerns about a medicine through the MHRA Yellow Card scheme as well¹⁹; reports help regulators monitor safety.

05 · Contraception and the pill

Contraception: the pill needs a back-up

Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed.¹ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ This applies to the pill only — implants, coils and injections are unaffected.⁷

An unplanned pregnancy on treatment is the situation the label is trying to prevent, and the pill is the method most affected by slower stomach emptying.

Dose increases happen several times during treatment, so the back-up window recurs. Many people find it simpler to move to a method that is not affected, such as an implant, coil or injection, and to talk this through with a GP or sexual health clinic before starting. Whichever route you choose, tell your prescriber what you use so that it is recorded.

Remember too that other medicines can be affected by the same slowing of the stomach. Because Mounjaro slows stomach emptying, it can affect how quickly some oral medicines are absorbed, particularly when you start treatment or increase the dose.¹ Tell your prescriber about everything you take, especially warfarin or other narrow-margin medicines, insulin, or sulfonylureas, where doses may need reducing to avoid low blood sugar.¹¹

06 · PCOS and fertility plans

PCOS, weight and fertility plans

If you have PCOS, weight loss is often part of the conversation about fertility, and treatment can fit into that picture when you meet the licensed criteria. Mounjaro is not licensed specifically for PCOS, but many women with PCOS meet the licensed weight-management criteria.⁴ Eligibility is assessed on the standard BMI criteria, which are a BMI of 30 kg/m² or above, or 27 kg/m² or above with a weight-related condition, for private treatment.

Mention PCOS and any fertility plans in your consultation. That allows the prescriber to think about timing, contraception and whether starting treatment now makes sense given your plans. It also means your later reviews can take account of any change in plans, such as deciding to start trying for a baby.

Weight loss can improve insulin resistance, cycles and symptoms, and improving weight can restore ovulation. The medicine is a tool for reaching that point, not a fertility treatment in its own right.

Our related guides go deeper on specific groups: how Mounjaro relates to fertility in women and the same question for men, plus a broader piece on GLP-1 medicines and male fertility.

07 · Other weight loss drugs

Ozempic, Wegovy and other weight loss drugs

Ozempic is semaglutide licensed for type 2 diabetes only; it is not a UK weight-loss medicine, and a regulated UK pharmacy will not supply it for weight loss. Always read the leaflet of the specific medicine you use and ask your prescriber about your own circumstances.

If you want to compare how these medicines differ in how they work, tirzepatide activates two natural gut-hormone receptors, GIP and GLP-1, while semaglutide, the active ingredient in Wegovy and Ozempic, is a single-action GLP-1 medicine.¹

Do not use Mounjaro while pregnant or trying to conceive, use reliable contraception, and tell your prescriber about your plans before you start. For a broader overview, see our guide on whether weight loss drugs affect fertility and the explainer on GLP-1 medicines and fertility.

If you came here about a particular product sold as a quick fix, remember that dramatic weight-loss claims are a red flag. Anyone offering to supply a prescription medicine without a consultation or prescription is not operating safely, and that matters even more when pregnancy is a possibility.

08 · Mounjaro injection and fertility

Mounjaro and fertility: the key instructions

Do not use it in pregnancy, stop at least one month before trying to conceive, use a back-up if you rely on the pill, and tell your prescriber if you become pregnant.¹

If you are breastfeeding, discuss it with your prescriber. Current prescribing information indicates minimal transfer of tirzepatide into breast milk, and the decision should reflect your circumstances.¹

09 · Egg quality and infertility causes

Egg quality, age and the usual causes of infertility

A GP or fertility specialist can discuss your own situation and arrange tests.

Testing and specialist assessment are the proper route.

If you have been trying for a long time, or you have very irregular or absent periods, ask your GP for an assessment. It is better to start that conversation early and to share which medicines you take, including weight loss treatment.

10 · Getting treatment safely

NHS or private: getting treatment with fertility plans in mind

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Whichever route you take, treat fertility plans as part of the clinical picture. Our process is a free online consultation, a review by a GPhC-registered prescriber, dispensing by our registered pharmacy (GPhC 9012878), and free next-day tracked delivery in temperature-controlled packaging.

Treatment is supplied through official LillyDirect supply, with genuine KwikPens. Once a pen is in use, it can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away. Before first use, keep pens in the fridge at 2–8°C until the printed expiry date.¹ Ongoing monthly reviews are included, and repeat orders re-check suitability, with no auto-shipping, so a change in your plans can be raised at any review.

People with diabetes should read our guide on weight loss medication for diabetes, because insulin and sulfonylurea doses may need adjusting.