The difference between semaglutide, tirzepatide and retatrutide

The myth: more receptors automatically means a better medicine for you

The most common assumption floating around forums and social media right now is that retatrutide must be the obvious next step, three receptors sounds better than two, which sounds better than one. It's a tidy story, and if you've been researching GLP-1 medicines for a while you've almost certainly come across it. The reality is more careful.

Receptor count does not translate directly into weight loss, tolerability or clinical suitability. Each additional receptor pathway adds a different physiological effect alongside greater potential for side effects, and the clinical bar for licensing is not just about average weight loss figures, it is about benefit, risk and real-world use across a broad population. Retatrutide's phase 3 data are still being collected. No regulator, including the MHRA, has assessed it yet. It is not a medicine you can obtain in the UK through any pharmacy, and pages suggesting otherwise are misleading. The meaningful clinical question, right now, is the difference between tirzepatide and semaglutide, two licensed, regulated options with years of trial data behind them.

That does not mean retatrutide is irrelevant, understanding where it sits helps make sense of the whole landscape, and that is what this page does.

What each medicine actually does, and where the evidence stands

Semaglutide is a GLP-1 receptor agonist. It mimics a hormone released after eating, reducing appetite, slowing the rate at which the stomach empties and helping regulate blood sugar. In the STEP 1 trial, published in the New England Journal of Medicine, adults taking 2.4mg semaglutide weekly alongside lifestyle changes lost an average of around 15% of body weight over 68 weeks. That is a substantial result. Wegovy (the weight-management brand) holds a UK licence; Ozempic is also semaglutide but licensed solely for type 2 diabetes, and if you want to understand how Ozempic and Mounjaro differ from each other, including their distinct licensing and mechanisms, that distinction is worth reading about before making any decisions.

Tirzepatide adds GIP receptor activation alongside GLP-1. GIP is a second gut hormone involved in fat storage, appetite and insulin response. In the SURMOUNT-1 trial, also published in the New England Journal of Medicine, participants taking 15mg tirzepatide lost an average of around 20–21% of body weight over 72 weeks. The absolute kilogram difference between the two is clinically meaningful for many people. In the SURMOUNT-5 head-to-head trial (751 adults, 72 weeks), tirzepatide produced greater average weight reduction than semaglutide 2.4mg, as noted by the NICE appraisal of tirzepatide (TA1026). Both medicines carry a Black Triangle, meaning they are subject to additional MHRA monitoring.

Retatrutide targets GLP-1, GIP and glucagon receptors simultaneously. Phase 2 trial data suggested average weight loss of around 24% at the highest dose over 48 weeks, an impressive signal, but a 48-week phase 2 result is not the same as the larger, longer phase 3 evidence base that regulators require. No UK licence application has been publicly confirmed. Availability in the UK is not imminent, and there is no legitimate way to access it through a UK pharmacy today.

Side-by-side: the key facts at a glance

A fuller look at how the two licensed options compare on cost is covered on the tirzepatide vs semaglutide cost page.

So what does this mean if you're deciding between them?

If you're researching retatrutide, it is probably because you want the most effective option, and that instinct makes complete sense. Honestly, most people who reach this page have been told by someone online that it's available somehow, and are checking whether that is true. It is not, at least not through any UK-regulated pharmacy.

The clinically supervised choice right now is between Wegovy and Mounjaro. Both are licensed in the UK, both have robust phase 3 evidence, and both are recommended by NICE (TA875 for semaglutide) and TA1026 for tirzepatide, within their respective criteria. Which suits you depends on your BMI, your medical history, any medicines you take (particularly oral contraceptives, where tirzepatide carries a specific absorption caution) and your own preferences about injection frequency and device format. You can read more about how the two licensed medicines stack up on the Mounjaro vs Wegovy comparison page.

At nume, a real prescriber reviews your consultation the same day, not software, not an automated queue. They look at the full picture before recommending anything. Speak to our prescribers to find out which option your history points toward.