Can Weight Loss Injections Affect Fertility?

You're thinking about fertility, and you've been prescribed a weight loss injection

Picture this: you've been assessed as suitable for a GLP-1 or dual-agonist weight loss injection, and somewhere in the back of your mind sits the question of starting a family, now, soon, or just at some point. That question deserves a proper answer, not reassurance that glosses over the detail.

The regulatory position is clear. Mounjaro (tirzepatide) and Wegovy (semaglutide) are both not recommended during pregnancy, while breastfeeding, or if you are actively trying to conceive. This is stated in each medicine's licensed information and reflected in NHS England's guidance on weight-management injections. The reason isn't that these medicines are proven harmful to fertility specifically, it's that safety data in pregnant humans is insufficient, and caution is the right clinical call when it is.

That means if pregnancy is something you're working towards right now, your prescriber needs to know before treatment starts. If you're already on treatment and your plans change, call your clinical team rather than simply stopping without advice, the timing of stopping and any wash-out period matters, and that decision belongs with a clinician who knows your case.

One practical habit worth building: when you book your next routine appointment with your GP or specialist, bring a written note of any fertility plans. A single sentence on paper is harder to forget to mention than a thought in your head during a busy consultation.

The contraception detail that often catches people off guard

For women using oral contraceptives alongside tirzepatide, there is a specific pharmacological point that goes beyond the general pregnancy advice. Tirzepatide slows gastric emptying as part of how it works, and this can reduce the absorption of oral medicines taken at the same time, including the pill. The MHRA advises, and NHS Inform Scotland's guidance on weight-loss medication confirms, that women on tirzepatide should use a non-oral method of contraception (condoms, for example) for the first four weeks of treatment and for four weeks after every dose increase.

The current evidence does not show the same effect with semaglutide (Wegovy), though it is still a GLP-1 receptor agonist and still not suitable if you are pregnant or trying to conceive. NHS England recommends that women on tirzepatide also consider switching to a transdermal form of HRT (patches or gels rather than oral tablets) for the same absorption reason, if HRT is part of their care.

None of this means these medicines are unsafe for women who are not trying to conceive. It means the contraception conversation needs to happen explicitly at the start of treatment, not assumed. A prescriber who doesn't ask about this is missing a step; one who does is doing their job properly. You can read more about how the treatment journey works on our weight loss injections overview.

What weight loss itself does for fertility, and why that matters here

Separating the medicine from the outcome it produces is important on this topic. Obesity is independently associated with hormonal disruption: raised oestrogen from adipose tissue, disrupted LH/FSH ratios, insulin resistance, and in some people, conditions like polycystic ovary syndrome (PCOS) that directly affect ovulation. The NHS patient information for tirzepatide makes clear that the medicine is a tool for weight management alongside dietary change and increased activity, and for many people, meaningful weight loss improves menstrual regularity, normalises ovulation and improves markers of reproductive function.

Clinical trial programmes for both tirzepatide and semaglutide were not specifically designed to measure fertility endpoints, so direct data on conception rates is limited. What exists is mostly observational: studies in people with obesity and PCOS showing improved cycle regularity and ovulation rates following significant weight loss, regardless of the method used to achieve it.

The honest framing is: weight loss achieved with clinical support may improve some fertility-relevant hormonal markers, but the injections themselves are stopped before any attempt at conception. The goal is to reach a healthier weight, then plan accordingly with your specialist. Our detailed page on weight loss injections and fertility explores the evidence on both sides of this in more depth.

Who to talk to, and when

This is a situation where the right conversation has more than one person in it. Your GP or a reproductive specialist understands your fertility history; a prescriber who knows your weight-loss treatment understands the pharmacology. Both perspectives matter, and they shouldn't happen in silos.

If you are considering starting a weight loss injection and have active fertility questions, raise both at your consultation. A GPhC-registered Independent Prescriber reviewing your case can factor in your reproductive plans, discuss the contraception requirements for your specific medicine, and help you think through the timing, including whether weight loss injections can cause infertility, a question our clinical team addresses in full. Questions about eligibility criteria for these treatments are covered on our eligibility page.

If you're already on treatment and your circumstances change (a new relationship, a change of plans, a positive test) the right step is to contact your prescriber promptly, not to make the call alone. Stopping abruptly without guidance isn't always the safest approach either; the conversation matters. It's also worth knowing that how weight loss injections affect your liver is another area our prescribers can walk you through if wider health questions come up during treatment. Our team is reachable seven days a week, and you can also get in touch directly if a specific question comes up between consultations.

For anyone who wants to explore treatment options first, speaking to our prescribers is the natural starting point, it's free, and the clinical review considers your full picture before anything is prescribed, including how weight loss injections can affect muscle mass, which is worth understanding as part of any longer-term health conversation.