Retatrutide Phase 3 Results: The Weight Loss Jab That Beats Surgery — But You Cannot Get It Yet

New trial data shows retatrutide helped people lose nearly a third of their body weight on average — results that rival bariatric surgery. But the drug is not approved in the UK, and experts say realistic access is still at least 18 months away. Here is everything you need to know right now.

A weight loss injection has just posted the most impressive clinical trial results ever recorded for a medicine in this class. Retatrutide phase 3 results, published on 21 May 2026 from the TRIUMPH-1 trial, show an average body weight loss of 28.3 percent over 80 weeks on the highest dose [Eli Lilly / ClinicalTrials.gov, May 2026]. To put that in plain English: someone starting at 15 stone could expect to lose more than four stone on average.

That is extraordinary. For comparison, Mounjaro — currently the strongest approved weight loss jab in the UK — produced around 20 to 22 percent weight loss in its own trials [NICE, 2023]. Retatrutide has cleared that bar by a significant margin.

But here is the part that will genuinely surprise you. Nearly half of all participants — 45.3 percent — lost 30 percent or more of their body weight [Eli Lilly / ClinicalTrials.gov, May 2026]. Thirty percent is the threshold doctors use to describe results equivalent to bariatric surgery, meaning a gastric bypass or sleeve gastrectomy. An injection achieving what surgery achieves, in nearly half of patients, is a landmark moment in medicine.

What exactly is retatrutide, and how is it different?

Most weight loss jabs you have heard of work on one or two hormone pathways in the body. Ozempic and Wegovy target one receptor — called GLP-1 — which controls appetite and blood sugar. Mounjaro targets two receptors: GLP-1 and GIP. Both approaches have proven highly effective.

Retatrutide goes one step further. It targets three receptors simultaneously: GLP-1, GIP, and a third called glucagon. This triple action is why researchers and clinicians have been watching this drug so closely. It does not just reduce appetite — it also appears to increase how much energy the body burns at rest [New England Journal of Medicine, 2023, Phase 2 data]. Think of it as pressing three different brakes on weight gain at once, rather than one or two.

The drug is made by Eli Lilly, the same company behind Mounjaro. It is a weekly injection, administered in the same way as Mounjaro — a small pen you use yourself at home.

So can I get retatrutide in the UK?

No. Not yet — and not for a while. The MHRA — the UK’s medicine regulator, equivalent to Europe’s EMA — has not approved retatrutide [MHRA, as of May 2026]. Eli Lilly will need to submit a full dossier of trial data for review before that can happen. That process typically takes 12 to 18 months after submission.

Realistic UK availability, even if everything goes smoothly, is not expected before late 2027 at the earliest — and mid-2028 is considered more likely by analysts tracking the regulatory timeline [Eli Lilly investor guidance, 2026]. That is not a reason for despair. It is simply the reality of how medicine works in a country with rigorous safety standards, which ultimately protects you.

If you see any clinic or website claiming to offer retatrutide now, treat that as a serious red flag. An unapproved drug being sold for weight loss outside a clinical trial is not legal in the UK, and the safety profile outside controlled trial conditions is not fully established.

What did the trial actually look like?

The TRIUMPH-1 trial was a large-scale Phase 3 study — the final and most rigorous stage of drug testing before regulatory submission. Phase 3 trials involve thousands of participants, use placebo controls (meaning some people receive a dummy injection so results can be compared fairly), and run for long enough to capture meaningful weight loss and safety data.

The 80-week duration matters. Many earlier weight loss trials ran for 52 weeks or less. Eighty weeks gives a much clearer picture of whether results hold up over time — and in this case, they did [Eli Lilly / ClinicalTrials.gov, May 2026].

The highest dose tested produced that headline 28.3 percent average weight loss. Lower doses also performed well, though specific figures for those arms had not been fully published at the time of writing. Full data is expected to be submitted to peer-reviewed journals in the coming months.

What about side effects?

The retatrutide phase 3 results data released so far does not include a complete side effect breakdown. However, Phase 2 data published in the New England Journal of Medicine in 2023 gives us a useful early picture. The most commonly reported side effects were nausea, vomiting, diarrhoea, and constipation — the same pattern seen with Mounjaro and Ozempic [NEJM, 2023].

These are typically worst in the first few weeks of treatment, as the dose is gradually increased. Most participants in trials manage them well enough to continue. A minority do stop treatment because of them.

There is one additional consideration worth knowing now. In January 2026, the MHRA strengthened warnings on the entire GLP-1 and dual GLP-1/GIP class of drugs — including Ozempic, Wegovy, and Mounjaro — after post-marketing data revealed rare cases of severe pancreatitis, an inflammation of the pancreas [MHRA, January 2026]. Retatrutide, as a drug in a related class, will face similar scrutiny. Long-term safety monitoring in large real-world populations always reveals things clinical trials cannot fully capture. That is not a reason to panic — it is a reason to stay informed.

Should you wait for retatrutide, or start treatment now?

This is the question many readers will be asking. The honest answer depends on your personal situation, and only a doctor can advise you properly. But here is a framework for thinking it through.

If you are eligible for Mounjaro right now — either through the NHS or through a reputable private provider — the evidence for its effectiveness is already very strong. Average weight loss of 20 to 22 percent is clinically significant [NICE, 2023]. Waiting 18 to 24 months for a drug that may produce better results means 18 to 24 months of carrying excess weight and its associated health risks.

On the other hand, if you have tried GLP-1 or dual GLP-1/GIP treatments before and not responded well, or if you are managing conditions that make the current options less suitable, retatrutide could represent a meaningfully different option worth waiting for.

What you should not do is buy anything claiming to be retatrutide from an online clinic or compounding pharmacy right now. Retatrutide phase 3 results are promising — but the drug is unapproved, unregulated, and unavailable through any legitimate UK channel [MHRA, May 2026].

What happens next?

Eli Lilly is expected to begin regulatory submissions in major markets — likely the United States first — in the second half of 2026. A UK submission to the MHRA would follow, after which the clock on formal review begins. NHS access, if and when it comes, would then go through a separate health technology assessment by NICE — the body that decides what the NHS will pay for — which adds further time.

We will cover every significant development in the retatrutide regulatory journey as it happens. If you want to be notified when the MHRA submission is made or when trial data is published in full, bookmark this page and check back regularly.

For now, the headline is simple. The retatrutide phase 3 results are the most impressive weight loss drug data ever published. The drug works extraordinarily well in trials. And you cannot have it yet — but the wait, if the science holds, may be worth it.

This article is for information purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any treatment.