Semaglutide or Retatrutide: What Does the Evidence Actually Show?

What the retatrutide phase 2 trial reported, and what that does and doesn't tell us

The headline figure that draws people to this search is striking. In a phase 2 trial published in the New England Journal of Medicine in 2023, adults with obesity taking the highest dose of retatrutide lost around 24% of body weight on average over 48 weeks. That is a larger number than any single-agent trial had previously produced.

Retatrutide works differently from semaglutide. It activates three separate hormone receptors: GLP-1, GIP and glucagon. GLP-1 reduces appetite and slows gastric emptying, much as semaglutide does. GIP may amplify that effect. Glucagon receptor activation raises metabolic rate and increases fat burning. The triple-agonist mechanism is the reason researchers believe retatrutide outperforms GLP-1-only medicines in energy expenditure, not appetite suppression alone. If you want to understand how the treatment landscape shifts as you move from semaglutide to retatrutide, the mechanistic gap matters clinically. Retatrutide and semaglutide are genuinely different molecules, and that difference is worth understanding.

But phase 2 trials are designed for safety and dose-finding, not definitive proof of efficacy across large populations. The participant numbers were modest; there was no direct comparison arm against semaglutide 2.4mg; and the 48-week timeline differs from STEP 1's 68 weeks. Quoting the two figures side by side as though they answer the same question is appealing, and understandable, but it is not how the science works. Phase 3 trials are under way; until those report and a regulator reviews them, the 24% figure is a promising signal, not a settled fact.

Where semaglutide actually stands right now

It is worth being clear about what semaglutide has that retatrutide does not: a complete regulatory record. The STEP 1 trial randomised nearly 2,000 adults and reported around 15% average weight reduction at 68 weeks at the 2.4mg weekly dose, published in the NEJM. That evidence base supported MHRA approval, a NICE technology appraisal (TA875), and NHS commissioning through specialist weight management services.

The UK now also has higher doses available. A 7.2mg weekly maintenance dose was approved by the MHRA in January 2026, and a dedicated single-dose 7.2mg pen followed in April 2026. Early data at 7.2mg pointed to roughly 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide considerably. If you are thinking about what semaglutide treatment looks like in practice, those numbers are the ones to hold in mind, not a comparison against a drug that has no licence yet.

Semaglutide also now carries MHRA approval for reducing major cardiovascular event risk in eligible adults, and from July 2026 a conditional approval for MASH, a form of liver disease. Its clinical profile extends well beyond weight loss alone, a fact that rarely features in the comparison searches.

Why retatrutide cannot be obtained in the UK, and the risk of trying

If you've been searching for retatrutide because the early trial numbers excited you, that is completely understandable. The honest answer is that it is not available anywhere as a licensed prescription medicine. No regulator (not the MHRA, not the FDA, not the EMA) has approved it. That means no legitimate pharmacy can dispense it, and any seller claiming otherwise is selling something that has bypassed every safety check a medicine goes through before it reaches patients.

The MHRA has been explicit about this pattern. Its warnings about counterfeit and illicit weight-loss injections (including the raid on an unlicensed manufacturing site in October 2025) describe exactly the market that unregulated compounds like retatrutide fill. Unlicensed products carry unknown purity, unknown dosing and no pharmacovigilance. If you are curious about what combining semaglutide and retatrutide would actually involve, that is a question worth approaching carefully and only in the context of future licensed use. Right now, the question is what is safe and legal today.

You can verify any online pharmacy dispensing weight-loss medicines by checking the GPhC pharmacy register. Legitimate pharmacies will be listed; sellers of unlicensed compounds will not. Worth checking before you hand over payment or personal details to any site.

Choosing the right treatment with current evidence

For most people arriving at this comparison, the practical question underneath it is: am I on the best treatment available to me right now? That is a fair thing to ask. Semaglutide at 2.4mg, and now at up to 7.2mg, is genuinely effective for most people who tolerate it. Tirzepatide, which activates GIP and GLP-1 as a dual agonist, is currently the most effective licensed option in the UK with an even broader body of evidence. Understanding the cost of Wegovy is a reasonable next step if you are weighing up whether to start.

Retatrutide's phase 3 results will be watched closely. If they replicate the phase 2 signals and a regulator approves the medicine, it will deserve a proper place in the conversation. Until then, comparing it with semaglutide as a genuine treatment choice puts an unlicensed compound in a bracket it hasn't earned yet.

If you are unsure whether semaglutide or another licensed treatment is right for you, the clearest route is a clinical conversation. The prescribers at nume review every consultation personally. Speak to our prescribers to work through your options based on your medical history, not a search result.