Which weight loss injection works best for PCOS?

What the trial data actually showed, and what it means for PCOS

The clearest evidence comes from the SURMOUNT-1 trial, published in the New England Journal of Medicine, which found that tirzepatide at 15mg produced an average body-weight reduction of around 20-21% over 72 weeks in adults with obesity. The STEP 1 trial, also in the NEJM, reported approximately 15% average weight loss with semaglutide 2.4mg over 68 weeks. Neither trial recruited exclusively for PCOS, but both included participants with insulin resistance and metabolic dysfunction, conditions that sit at the centre of most PCOS presentations.

Why does that matter specifically here? PCOS-related weight gain is frequently driven by hyperinsulinaemia: chronically elevated insulin drives fat storage and makes weight loss harder through diet alone. GLP-1 receptor agonists reduce postprandial insulin secretion in a glucose-dependent way and slow gastric emptying, which lowers appetite and calorie intake. Tirzepatide also activates GIP receptors, adding a second hormonal pathway. In practice, women with PCOS often tell our prescribers that previous diet attempts produced little change; the metabolic mechanism here is different.

The head-to-head SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found that tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks in adults with obesity. That's a meaningful finding for anyone choosing between the two, though it doesn't make one universally better, individual tolerability, medical history and concurrent medications matter as much as headline trial figures. If you'd like a plain-English overview of both injections, the weight loss injections guide on our site covers how each one works in practice.

The contraception and fertility picture you need before starting

This section carries extra weight for women with PCOS, many of whom are in their reproductive years and may be navigating fertility questions at the same time as weight management.

The MHRA advises using effective contraception while on GLP-1 medicines and for a period afterwards before trying to conceive. For tirzepatide specifically, NHS guidance notes that women taking oral contraceptive pills should also use a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide's effect on gastric emptying may reduce pill absorption. There is no equivalent evidence of this effect for semaglutide, though contraception is still strongly advised.

Mounjaro, Wegovy and the newer oral semaglutide tablet are all not recommended during pregnancy, during breastfeeding, or when actively trying to conceive, this isn't a caution to weigh up, it's a clear clinical boundary. If a pregnancy is planned, your prescriber will advise on an appropriate wash-out period before stopping contraception. Women receiving fertility treatment should discuss timing explicitly with both their fertility specialist and the prescribing clinician. NHS England's guidance on weight management injections covers these contraception considerations in full and is worth reading alongside any consultation.

Our prescribers review each case individually. If you want to explore your options, whether weight loss injections can help with PCOS is a question we've addressed separately, with more on the hormonal context.

What's uncertain, and what a prescriber considers that an article can't

There's no randomised controlled trial to date that has tested tirzepatide or high-dose semaglutide as a primary treatment for PCOS as a condition, rather than as a weight management tool in people who happen to have it. That distinction matters. Some observational data and smaller studies suggest improvements in menstrual regularity and androgen levels alongside weight loss, but these aren't yet part of the licensed indications and shouldn't be treated as guaranteed outcomes.

Other uncertainties specific to PCOS: some women with the condition take metformin, combined oral contraceptives, or hormonal treatments simultaneously. Interactions with GLP-1 medicines are generally manageable but need prescriber review. Women on oral HRT alongside tirzepatide may be advised to consider transdermal formulations instead, for the same absorption reason as the pill. These aren't reasons to avoid treatment, they're reasons to have a proper assessment rather than buying anything without one.

Choosing between the two injections isn't something to resolve from a comparison article. A PCOS-specific medical history, current medications, BMI, and personal priorities all shape the decision. Our clinical team (details on the our clinical team page) reviews every consultation personally, the same working day, before anything is prescribed. There's a wider look at how the two medicines compare on the which injection is right for me page if you want to read more first.

How to access treatment and what happens in practice

Both Mounjaro and Wegovy are prescription-only medicines, which means the legal route involves clinical assessment by a qualified prescriber, not a quiz that ends in a checkout. Legitimate UK online pharmacies carry a GPhC registration number you can verify instantly; ours is 9012878, searchable on the GPhC pharmacy register.

At nume, the process is straightforward. You complete a free consultation, a GPhC-registered Independent Prescriber reads it the same day, and if treatment is appropriate you'll receive confirmation. Orders placed before noon on a working day are dispatched the same day, and DPD delivers to your door the next working day, tracked, in a plain box with nothing identifiable on the outside. The pen itself is a pre-filled KwikPen, small enough to fit in a coat pocket, and each one covers four weekly doses.

If cost is a factor, how much weight loss injections cost walks through market pricing honestly, including what a transparent single price should cover. For the practicalities of the injection itself, our guide on choosing the best injection site is worth reading before you start. And if you have questions that aren't answered here, the FAQs page covers the ones our prescribers hear most often, including questions about extreme weight loss injections and whether higher-intensity options are appropriate for your situation.

Ready to find out if either injection is suitable for you? Start your free consultation and a prescriber will review your case (including your PCOS history) the same day.