Which weight loss injection is cheapest — and is that the right question?

What trial results say about the medicines you're comparing

The clinical case for GLP-1 and dual-agonist weight loss injections is unusually robust. In the SURMOUNT-1 trial, tirzepatide (Mounjaro) produced an average body-weight reduction of around 20–21% over 72 weeks at the highest dose, findings published in the New England Journal of Medicine. Semaglutide (Wegovy) delivered around 15% average weight loss over 68 weeks in its STEP 1 trial, again published in the NEJM. These aren't comparable numbers to casual dieting results; they represent the most effective licensed medicines for weight management currently available in the UK.

In a direct head-to-head (the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025) tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks. NICE's appraisal of tirzepatide (TA1026) referenced this comparison in its committee discussion. Greater average efficacy doesn't automatically make one medicine right for every person, but it is relevant context when you're weighing cost against clinical outcomes.

The point here isn't to promote one pen over another. It's that these are serious prescription medicines with meaningful differences, and price alone doesn't map onto that complexity.

How UK private pricing actually works, and what headline costs often leave out

A question our prescribers hear most weeks is some version of: "I've seen it advertised for less, why the difference?" The honest answer is that headline prices vary widely because providers bundle different things into them. Some figures you'll see online include only the medicine. Others omit the consultation fee, the prescription charge, delivery, or ongoing clinical support between doses.

Eli Lilly raised Mounjaro's UK list price from 1 September 2025; the highest-dose pen's list price rose to around £330, and reported private prices across providers since then range roughly £149 to £375 per month depending on the dose and what's included. These figures are widely reported and worth knowing as context, but they tell you nothing about what clinical oversight accompanies them. If you're trying to work out what are the cheapest weight loss injections once all the costs are factored in, you can find a broader breakdown of how costs are structured on our UK weight loss injection cost guide.

At nume, one transparent price covers the consultation, the prescription, the treatment, delivery, and aftercare. We lose the price comparison on purpose. The trade-off (same-day clinical review, a named GPhC-registered prescriber, identity-verified dispensing from our own GPhC-registered pharmacy) is one we think is worth making plainly, rather than burying it. Pricing is shown in full on our treatment page; there are no subscriptions and no automatic renewals.

Why 'cheapest' is the wrong test for a prescription medicine

The MHRA has warned publicly and repeatedly about counterfeit weight loss pens sold online, some of which have been found to contain insulin rather than the labelled medicine. In October 2025, the first illicit UK site manufacturing fake tirzepatide pens was raided; enforcement in 2025 alone accounted for around 20 million doses of illegally traded weight loss medicines (roughly £45m street value). The pattern the regulator describes is consistent: sellers offering these medicines without a prescription, often via social media, frequently with prices well below the legitimate market. You can report suspect sellers directly through the MHRA's Yellow Card scheme.

Any legitimate private provider, however it prices its service, is operating through the licensed UK supply chain, with clinical assessment and a verifiable GPhC registration. You can check whether an online pharmacy is registered using the GPhC's public register; nume's registration number is 9012878. A provider that can't be found there is a red flag, regardless of price. If you're asking yourself what's the cheapest weight loss injection from a legitimate, registered provider, that question is worth separating clearly from anything sourced outside the licensed supply chain.

For context on how much weight people typically lose on these treatments, and what realistic expectations look like, our page on weight loss injection results covers the trial evidence in detail. If you're still deciding which treatment might suit your situation, and want to understand what's the cheapest weight loss injection for your particular starting dose and circumstances, the weight loss treatment overview is a good starting point before a consultation.

The cheapest listing, if it comes without a real prescriber, a verifiable supply chain, and clinical follow-up, isn't a bargain. It's a different product entirely.