The 3 Weight Loss Injections Available in the UK — and How to Choose

What separates Mounjaro, Wegovy, and Saxenda from each other?

The decision between these three injections starts with mechanism. Liraglutide (Saxenda, made by Novo Nordisk) was the first to be licensed in the UK for weight management and mimics GLP-1, a gut hormone that slows stomach emptying and reduces appetite. Semaglutide (Wegovy, also Novo Nordisk) works on the same receptor but is a more potent, longer-acting molecule, hence a once-weekly rather than daily injection. Tirzepatide (Mounjaro, Eli Lilly) goes further still: it targets both GIP and GLP-1 receptors simultaneously, making it the only dual-agonist weight-loss medicine with a UK licence.

That biological difference shows up in the trial data. In the STEP 1 trial, semaglutide 2.4mg produced an average weight reduction of around 15% over 68 weeks. Tirzepatide, in the SURMOUNT-1 trial, produced around 20–21% average reduction at the 15mg maintenance dose, and in the SURMOUNT-5 head-to-head comparison, tirzepatide produced greater average weight loss than semaglutide 2.4mg directly. Liraglutide's average results in its pivotal trial were more modest, typically in the 5–8% range, though individual responses vary considerably with any of these medicines.

You can read more about how weight loss injections work as a category if you want the fuller picture on mechanisms before looking at individual products.

Which one actually fits your situation?

Licensing, not preference, sets the outer boundary here. All three are licensed for adults with a BMI of 30 or above, or 27 and above if at least one weight-related condition is present, things like high blood pressure, raised cholesterol, type 2 diabetes, or obstructive sleep apnoea. Lower BMI thresholds apply for certain ethnic backgrounds under UK guidance. A prescriber assesses the full picture; BMI alone is never the whole story.

Beyond eligibility, the practical shape of your life matters. Saxenda's daily injection schedule suits some people and feels like too much for others. Wegovy and Mounjaro are both once a week, which many find easier to build into a routine. Injection frequency is worth raising at your consultation rather than deciding in isolation.

Saxenda is not currently dispensed by nume, our prescribers work with Mounjaro and Wegovy. If you're trying to decide between those two specifically, the comparison of the top three weight loss injections covers the evidence side by side in more detail.

Cost is part of the picture too. Private treatment prices vary significantly between the three medicines and between providers. The breakdown of weight loss injection costs in the UK covers what a legitimate price should include, and why headline figures from unverified sellers often miss important parts of the picture.

Side effects: what's shared and what differs

All three injections share a broadly similar side-effect profile, because they all slow gastric emptying. Nausea is the most commonly reported issue, particularly in the first few weeks and after each dose increase. Vomiting, diarrhoea, constipation, and reflux are also reported. These effects are generally most pronounced early in treatment and tend to settle as the body adjusts.

Tirzepatide's dual mechanism means its gastrointestinal side effects have been characterised separately in its own trial programme; the pattern is comparable to GLP-1 medicines but the clinical profile is not identical. The detailed guide to what these three injections are covers the side-effect data for each one in its own section.

On safety, the NHS medicines page for tirzepatide and the NHS medicines page for semaglutide both list what to watch for and when to seek urgent help, including symptoms of pancreatitis (severe, persistent stomach pain that may radiate to the back), which the MHRA flagged as a known but infrequent risk across GLP-1 medicines in a Drug Safety Update issued in January 2026. If you experience something like that, contact a doctor promptly rather than waiting for your next review.

People taking other medicines (or managing conditions like hypothyroidism alongside a weight loss injection) should raise those details at the clinical assessment stage. The prescriber needs the full picture to make a safe decision. That applies equally to anyone asking whether weight loss injections are safe alongside methotrexate.

NHS access, private routes, and what to do next

The NHS route for these medicines is real but narrow at the moment. Tirzepatide (Mounjaro) is being rolled out in primary care under a phased commissioning framework linked to NICE guidance; early cohorts require a BMI of 40 or above alongside multiple specific health conditions, and the criteria expand gradually over time. Wegovy is available through specialist weight management services but waiting lists are commonly long. Liraglutide (Saxenda) sits outside the phased rollout framework.

For people who don't meet the current NHS thresholds, or who prefer not to wait, the private route through a regulated online pharmacy is the practical alternative. If you want to understand how that compares to the GP route specifically, the page on getting weight loss injections through your GP lays out the differences plainly.

One thing worth knowing: many people plan their start date around their finances. If you order by midday on a weekday (whether that's payday or the first Monday back after a bank holiday) a prescription review happens the same day if clinically suitable, with dispatch and free next-working-day delivery following from there.

If you're ready to find out which of these medicines you might be suitable for, start your free consultation and a GPhC-registered prescriber will review your answers the same day. No waiting room. No algorithm making the call.