Retatrutide UK
What is retatrutide and when is it coming to the UK?
The plain English guide to the next generation weight loss jab. The latest Phase 3 results explained, including TRIUMPH-1 and the full TRIUMPH-2 results published in The Lancet, and what UK patients need to know right now.
What is retatrutide?
Retatrutide is an investigational once-weekly weight loss injection being developed by Eli Lilly, the same pharmaceutical company that makes Mounjaro.
It is a triple hormone receptor agonist, activating receptors for GLP-1, GIP and glucagon. Mounjaro, which contains tirzepatide, activates GLP-1 and GIP receptors, while semaglutide medicines such as Wegovy act on GLP-1 receptors.
These pathways influence appetite, food intake, blood glucose and energy metabolism in different ways. The addition of glucagon receptor activity is one of the features that distinguishes retatrutide from currently approved GLP-1-based weight-management medicines.
The important point is that retatrutide remains investigational. It has now produced substantial weight loss across several Phase 3 trials, but it has not yet been approved for routine use in the UK.
What did the TRIUMPH-1 trial actually show?
Eli Lilly announced topline results from the Phase 3 TRIUMPH-1 trial in May 2026, and the full results were published in the New England Journal of Medicine on 29 September 2026. The trial enrolled 2,339 adults with obesity or overweight and at least one weight-related complication, without diabetes, and compared retatrutide with placebo over 80 weeks.
Using Lilly’s efficacy estimand, which estimates the effect if participants remained on their assigned treatment without starting prohibited weight-management therapies, participants taking 12 mg retatrutide lost an average of 28.3 percent of body weight at 80 weeks. The 9 mg group lost 25.9 percent and the 4 mg group 19.0 percent, compared with 2.2 percent with placebo.
At the 12 mg dose, 45.3 percent of participants achieved at least 30 percent weight loss. That is an unusually large reduction for a drug trial, although it should not be described as equivalent to bariatric surgery for every patient because surgery and medicines have different evidence bases, risks and long-term outcomes.
TRIUMPH-1 also included a pre-specified extension involving 532 participants who had a BMI of at least 35 at baseline and completed the main study on treatment. In that extension, participants originally assigned to the 12 mg arm and escalated to their maximum tolerated dose lost an average of 30.3 percent at 104 weeks under the efficacy estimand.
The treatment-regimen estimand, which includes the effects of treatment discontinuation and use of prohibited weight-management therapies, produced lower but still substantial figures: 25.0 percent average weight loss at 80 weeks for the 12 mg group and 29.9 percent at 104 weeks in the extension. These different analyses are important context when interpreting the headline 28.3 and 30.3 percent figures.
Retatrutide UK vs Mounjaro
This is one of the questions UK readers are most likely to ask, but there is an important limitation: retatrutide and Mounjaro have not been compared in a completed head-to-head Phase 3 obesity trial.
Across separate trial programmes, the highest-dose retatrutide arm in TRIUMPH-1 produced 28.3 percent average weight loss at 80 weeks under the efficacy estimand. In the pivotal SURMOUNT-1 trial, the highest tirzepatide dose produced average weight loss of about 20.9 percent at 72 weeks. Those figures come from different studies, populations, durations and statistical approaches, so they should not be treated as a direct contest.
The numbers are lower for both medicines in people with type 2 diabetes, who typically lose less weight on these treatments. In TRIUMPH-2, retatrutide 12 mg produced 18.8 percent average weight loss at 80 weeks, counting everyone who started the trial. In tirzepatide’s SURMOUNT-2 trial, also in people with obesity and type 2 diabetes, the 15 mg dose produced 14.7 percent at 72 weeks using the same kind of analysis. These are still separate trials rather than a head-to-head comparison.
Retatrutide activates the glucagon receptor in addition to GIP and GLP-1, whereas tirzepatide activates GIP and GLP-1 receptors. Whether that translates into better outcomes for a particular patient cannot be determined from cross-trial percentages alone.
What can be said is that retatrutide has produced very large average weight reductions in Phase 3 trials. Mounjaro, meanwhile, is already an approved UK medicine with a much larger body of clinical and real-world experience.
The evidence base for retatrutide is still developing. TRIUMPH-1 and TRIUMPH-2 were published in full in September 2026, in the New England Journal of Medicine and The Lancet respectively, but full peer-reviewed publications from TRIUMPH-3 and TRIUMPH-4 are still awaited, and long-term post-marketing safety data cannot exist until the medicine is approved and used routinely.
For a broader comparison of the evidence across current and emerging treatments, see our weight loss jabs and pills compared guide, and our retatrutide vs Mounjaro explainer for why cross-trial comparisons need care.
Should I wait for retatrutide or start Mounjaro now?
This is an important practical question, but it cannot be answered safely from headline weight-loss percentages alone.
Mounjaro is already authorised in the UK for weight management in eligible adults, while retatrutide remains investigational. Someone who is considering starting, stopping or changing a prescribed treatment should discuss that decision with their prescriber rather than delay or alter treatment solely because of an investigational drug’s trial results.
Retatrutide’s Phase 3 results are encouraging, but there is no confirmed UK launch date and no completed head-to-head Phase 3 obesity trial showing how it compares directly with Mounjaro in the same population.
If retatrutide is eventually authorised in the UK, prescribers will be able to consider its approved indication, safety information and an individual’s treatment history at that time. Until then, it should not be treated as an available alternative to an approved medicine.
What you should not do is buy products sold online as retatrutide outside a legitimate clinical trial. Lilly states that retatrutide is investigational and legally available only to participants in its clinical trials. Products marketed elsewhere as retatrutide have not been approved by the MHRA for routine treatment.
UK approval timeline – realistic expectations
Retatrutide is not approved in the UK. As of 30 September 2026, no UK marketing authorisation or confirmed UK launch date has been announced. In July 2026 the MHRA warned that retatrutide has not been authorised for use in the UK and that anyone selling it is doing so illegally.
There has, however, been a relevant UK regulatory development. On 16 July 2026 the MHRA published a decision agreeing a paediatric investigation plan for retatrutide in obesity and overweight. A paediatric investigation plan is part of medicine development and sets out how a medicine will be studied in children where appropriate. It is not the same thing as a marketing authorisation and does not mean retatrutide has been approved for sale or prescribing in the UK.
In July 2026 Lilly said the positive Phase 3 programme had provided the clinical data package to support global regulatory submissions and confirmed that it plans to submit a Biologics License Application to the US FDA in Q1 2027. It restated that plan when the full TRIUMPH-2 results were published on 29 September 2026. Lilly has not announced a date for a UK marketing authorisation application.
That means any precise prediction for UK approval or launch would currently be speculation. If retatrutide receives UK marketing authorisation, NHS use would then depend on separate NICE appraisal and commissioning decisions. Private availability and NHS access do not necessarily begin at the same time.
Where things stand right now
TRIUMPH-1, TRIUMPH-2 and TRIUMPH-3 have all reported positive Phase 3 results. TRIUMPH-1 and TRIUMPH-2 were both published in full on 29 September 2026. TRIUMPH-2, in adults with obesity or overweight and type 2 diabetes, appeared in The Lancet, confirming the 20.8 percent average weight loss on 12 mg that Lilly first announced in July. TRIUMPH-3 studied adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes, and reported up to 22.6 percent average weight loss at 80 weeks.
Our full TRIUMPH-2 results explainer sets out what the published paper added, including how many people reached 20 and 25 percent weight loss and what happened to blood sugar.
Lilly plans to submit a Biologics License Application for retatrutide to the US FDA in Q1 2027 and says its Phase 3 programme now provides the clinical data package to support global regulatory submissions. No UK marketing authorisation or launch date has yet been announced. The MHRA did agree a paediatric investigation plan for retatrutide in July 2026, but that is a development requirement rather than a marketing authorisation.
Retatrutide remains investigational and is not an approved UK prescription treatment.
ThePeptideBrief will update this page when significant developments are announced — including regulatory submissions, approvals, NICE appraisal, pricing or confirmed availability dates.
Latest retatrutide developments
Retatrutide TRIUMPH-2 Results: What the Full Data Shows — full results published in The Lancet, September 2026
Retatrutide Phase 3 Results — What They Mean for UK Patients — TRIUMPH-2 and TRIUMPH-3 results announced July 2026
Eli Lilly Sues Six Companies Over Unlicensed Retatrutide Sales — August 2026
Six Cases of Liver Damage Linked to Grey Market Retatrutide — August 2026
Retatrutide Early Access Opens in the US — UK Patients Not Yet Eligible — August 2026
Is Retatrutide Becoming the New Steroids? — August 2026
Retatrutide side effects – what we know so far
Phase 3 results now provide a much broader safety picture than the earlier Phase 2 trial alone, and full safety data from TRIUMPH-1 and TRIUMPH-2 have now been published in peer-reviewed journals.
Across TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 and TRIUMPH-4, the most commonly reported adverse events with retatrutide were gastrointestinal, particularly nausea, diarrhoea, constipation and vomiting. Rates varied by trial and dose. In TRIUMPH-1, for example, nausea occurred in 42.4 percent of participants on 12 mg versus 14.8 percent with placebo, while diarrhoea occurred in 32.0 percent versus 13.5 percent.
Dysesthesia, an altered skin sensation that can include tingling or abnormal sensitivity, has also appeared across the Phase 3 programme. In TRIUMPH-1 it occurred in 12.5 percent of participants on 12 mg versus 0.9 percent with placebo. In TRIUMPH-2 the corresponding figures were 7.3 percent versus 0.7 percent, and in TRIUMPH-3 6.4 percent versus 1.3 percent. The published TRIUMPH-2 paper also reported low blood pressure (hypotension) more often with retatrutide: in 6 percent of people on 12 mg versus under 1 percent on placebo. Lilly reported that these events were generally mild to moderate and that most resolved during treatment. The trials establish an association with retatrutide treatment, but they do not establish that glucagon receptor activity is the cause.
Discontinuation because of adverse events has also varied between studies and doses. In TRIUMPH-1, 11.3 percent of participants on 12 mg discontinued because of adverse events versus 4.9 percent with placebo. In TRIUMPH-2 the figure was 7.7 percent on 12 mg versus 4.9 percent with placebo, while in TRIUMPH-3 it was 13.5 percent on 12 mg versus 4.8 percent with placebo.
The 2023 Phase 2 obesity trial also identified a dose-dependent increase in heart rate that peaked around 24 weeks and then declined. This remains relevant safety context, but it should not be presented as a newly established Phase 3 finding unless a specific Phase 3 analysis reports it.
The MHRA’s January 2026 pancreatitis warning applies to UK-authorised GLP-1 receptor agonists and dual GLP-1/GIP receptor agonists such as semaglutide and tirzepatide. Retatrutide is not yet authorised in the UK, so it is not covered by UK-approved product information. If approved, its final UK safety warnings will be determined from the regulatory review of the retatrutide evidence.
Longer-term and rarer risks will become clearer as the Phase 3 programme matures and, if retatrutide is approved, through post-marketing safety monitoring.
Retatrutide vs Wegovy – the honest comparison
Wegovy is the brand name for semaglutide used for weight management in the UK. Semaglutide acts on the GLP-1 receptor, while retatrutide activates GIP, GLP-1 and glucagon receptors.
The original STEP 1 trial of once-weekly semaglutide 2.4 mg reported average weight loss of about 14.9 percent at 68 weeks. The UK has since authorised a higher 7.2 mg Wegovy dose for adults with obesity, and in June 2026 the MHRA also authorised a daily Wegovy semaglutide tablet for weight management.
TRIUMPH-1 reported 28.3 percent average weight loss at 80 weeks with 12 mg retatrutide under the efficacy estimand. That figure is substantially larger than the result from the original 2.4 mg semaglutide trial, but it is still a cross-trial comparison rather than evidence from a direct head-to-head study.
The mechanisms are also different, but it is too simplistic to attribute the entire difference in weight loss to one receptor. Drug dose, trial population, duration, adherence and the combined pharmacology all matter.
For patients, the practical distinction today is that Wegovy is an approved UK medicine with established prescribing information, while retatrutide remains investigational. Whether retatrutide will ultimately offer better outcomes for a particular person cannot be known from separate trial averages alone.
On cost, see our Mounjaro price comparison for a live sense of current private GLP-1 pricing. No official UK price has been announced for retatrutide.
What will retatrutide cost in the UK?
No official UK price has been announced for retatrutide. Because the medicine is still investigational, any precise monthly price quoted now would be speculation.
Current prices for approved medicines such as Mounjaro and Wegovy can provide context for what private weight-management treatment costs today, but they cannot reliably predict Lilly’s future retatrutide price. See our Mounjaro price comparison for current Mounjaro figures.
If retatrutide receives UK marketing authorisation, the private price will depend on Lilly’s launch price, available doses, provider charges and the competitive market at that time.
NHS access would be a separate question. NICE would need to assess the treatment and its cost effectiveness before routine NHS use, and any recommendation could include specific eligibility criteria. Commercial arrangements between manufacturers and the NHS may also affect the price paid by the health service.
Until Lilly announces a UK price and the UK regulatory position is clearer, figures claiming that retatrutide will cost a particular amount per month should be treated as estimates rather than established facts.
Beyond TRIUMPH-1: what the other retatrutide trials show
TRIUMPH-1 is the headline general obesity trial, but Lilly’s retatrutide programme now covers several different obesity-related conditions and type 2 diabetes.
TRIUMPH-4, announced in December 2025, studied adults with obesity or overweight and knee osteoarthritis, without diabetes. At 68 weeks, participants taking 12 mg retatrutide lost an average of 28.7 percent of body weight under Lilly’s efficacy estimand and had substantial improvements in WOMAC knee pain scores. More than one in eight retatrutide-treated participants were reported to be free from knee pain at the end of the trial.
TRANSCEND-T2D-1 is a separate Phase 3 diabetes trial, now published in The Lancet. It studied adults with type 2 diabetes inadequately controlled by diet and exercise alone over 40 weeks and found significant improvements in HbA1c and body weight with retatrutide compared with placebo.
TRIUMPH-2 studied 1,152 adults with obesity or overweight and type 2 diabetes. Lilly announced topline results in July 2026, and the full results were published in The Lancet and presented at EASD on 29 September 2026. On 12 mg, average weight loss at 80 weeks was 20.8 percent if people stayed on treatment, which is Lilly’s headline figure, or 18.8 percent counting everyone who started the trial, including people who stopped. About half (52 percent) of people who stayed on 12 mg lost at least a fifth of their starting weight, and average HbA1c fell by 1.4 to 1.6 percentage points across the doses. Because everyone in TRIUMPH-2 had type 2 diabetes, these results should not be compared directly with the 28.3 percent from TRIUMPH-1, which studied people without diabetes. Read what the full TRIUMPH-2 paper shows.
TRIUMPH-3 studied adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes. Lilly reported up to 22.6 percent average weight loss at 80 weeks. These are topline results and detailed peer-reviewed publication is still awaited.
TRIUMPH-Outcomes, registered as NCT06383390, is a large cardiovascular and kidney outcomes study in adults with obesity and established atherosclerotic cardiovascular disease and/or chronic kidney disease. ClinicalTrials.gov currently lists the study as active, not recruiting, with no results posted. Its purpose is to test whether retatrutide reduces serious cardiovascular events and worsening kidney disease; those outcomes should not be assumed before the trial reports.
Taken together, the programme now extends well beyond a single weight-loss trial, but several important questions, particularly long-term cardiovascular, kidney and post-marketing safety outcomes, remain unanswered.
Swipe sideways to see the full table →
|
Treatment |
Average Weight Loss |
Receptors Targeted |
UK Status |
Live Pricing |
|---|---|---|---|---|
|
Retatrutide |
28.3% |
3 (GLP-1 GIP Glucagon) |
Not approved |
Coming soon |
|
Mounjaro |
20-22% |
2 (GLP-1 GIP) |
Approved |
|
|
Wegovy (injection) |
14.9-20.7% |
1 (GLP-1) |
Approved |
|
|
Ozempic |
12-15% |
1 (GLP-1) |
Diabetes only |
Coming soon |
|
CagriSema |
22-25% est |
2 (GLP-1 Amylin) |
Phase 3 trials |
Coming soon |
|
Wegovy Pill |
13.6% |
1 (GLP-1) |
Approved in UK |
Coming soon |
Frequently Asked Questions
When will retatrutide be available in the UK?
No official UK approval or launch date has been announced. Lilly plans a US FDA submission in Q1 2027 and says its Phase 3 data package can support global regulatory submissions. The MHRA agreed a paediatric investigation plan for retatrutide in July 2026, but this is not a UK marketing authorisation.
How does retatrutide compare to Mounjaro?
Retatrutide has produced higher headline average weight-loss figures in its Phase 3 obesity programme than tirzepatide produced in its pivotal obesity trials, but there is no completed head-to-head Phase 3 obesity trial comparing the two medicines directly. The studies used different populations, durations and statistical approaches, so the percentages should not be treated as a direct comparison.
Is retatrutide available to buy in the UK right now?
No. Retatrutide is not approved by the MHRA for routine treatment in the UK. Lilly states that it is investigational and legally available only to participants in its clinical trials. Products sold elsewhere as retatrutide are not MHRA-approved retatrutide medicines.
Should I stop Mounjaro and wait for retatrutide?
Do not stop or change prescribed Mounjaro solely because of emerging retatrutide trial results without speaking to your prescriber. Retatrutide remains investigational and is not currently an approved UK treatment. Treatment decisions should be based on your own medical circumstances and the advice of a qualified prescriber.
What were the TRIUMPH-1 trial results?
Eli Lilly announced Phase 3 TRIUMPH-1 topline results in May 2026. Under the efficacy estimand, the 12 mg group lost an average of 28.3 percent of body weight at 80 weeks and 45.3 percent achieved at least 30 percent weight loss. A pre-specified extension in participants with a baseline BMI of at least 35 reported 30.3 percent average weight loss at 104 weeks for the 12 mg-to-maximum-tolerated-dose group.
What did the TRIUMPH-2 trial show?
TRIUMPH-2 tested retatrutide in 1,152 adults with obesity or overweight and type 2 diabetes. On 12 mg, average weight loss at 80 weeks was 20.8 percent if people stayed on treatment, or 18.8 percent counting everyone who started the trial, including people who stopped. About half of those who stayed on 12 mg lost at least 20 percent of their starting weight. The full results were published in The Lancet on 29 September 2026.
What are the side effects of retatrutide?
Across the Phase 3 programme, the most common adverse events have been gastrointestinal, including nausea, diarrhoea, constipation and vomiting. Dysesthesia, an altered skin sensation, has also been reported and its frequency varies by trial and dose. Lilly has generally described these events as mild to moderate, with most resolving during treatment. A dose-dependent increase in heart rate was previously observed in the Phase 2 obesity trial.
Will retatrutide be available on the NHS?
Any NHS use would first require UK marketing authorisation and then NICE appraisal and commissioning decisions. No NHS availability date or eligibility criteria have been announced for retatrutide, so it is too early to give a reliable timetable.
What did the TRIUMPH-4 and TRANSCEND-T2D-1 trials show?
TRIUMPH-4 tested adults with obesity or overweight and knee osteoarthritis and reported 28.7 percent average weight loss at 68 weeks with 12 mg retatrutide under the efficacy estimand, alongside substantial improvement in knee pain. TRANSCEND-T2D-1, published in The Lancet in 2026, studied adults with type 2 diabetes inadequately controlled by diet and exercise and showed significant improvements in HbA1c and body weight over 40 weeks.
Is retatrutide being tested for heart health benefits like Wegovy?
Yes. TRIUMPH-Outcomes (NCT06383390) is testing whether retatrutide reduces serious cardiovascular events and worsening kidney disease in adults with obesity and established atherosclerotic cardiovascular disease and/or chronic kidney disease. ClinicalTrials.gov currently lists it as active, not recruiting, with no results posted, so no cardiovascular or kidney benefit should yet be assumed.
Sources and editorial methodology
Page last reviewed: 30 September 2026. This guide was compiled by The Peptide Brief editorial team and is checked against primary regulatory and clinical sources, not secondhand reporting. We accept no payment, sponsorship or affiliate commission from pharmaceutical manufacturers or private clinics.
Regulatory status: MHRA paediatric investigation plan decision for retatrutide in obesity and overweight, published 16 July 2026. This is not a marketing authorisation. MHRA public statement that retatrutide has not been authorised for use in the UK, 24 July 2026. No UK marketing authorisation or launch date has been announced as of this review.
Trial data: TRIUMPH-1 Phase 3 topline and 104-week extension results, Eli Lilly, 21 May 2026. Full TRIUMPH-1 results: Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity, New England Journal of Medicine, published online 29 September 2026 (doi:10.1056/NEJMoa2604169; ClinicalTrials.gov NCT05929066). TRIUMPH-2 and TRIUMPH-3 Phase 3 topline results, Eli Lilly, 23 July 2026. Full TRIUMPH-2 results: Bellido V, le Roux CW, Ekinci EI, et al., The Lancet, published online 29 September 2026 (doi:10.1016/S0140-6736(26)01861-1; ClinicalTrials.gov NCT05929079), and Eli Lilly detailed TRIUMPH-2 results release, 29 September 2026. TRIUMPH-4 topline results, Eli Lilly, December 2025. TRANSCEND-T2D-1, published in The Lancet, 2026 (PubMed ID 42250575, ClinicalTrials.gov NCT06354660). Phase 2 data: Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity, a Phase 2 Trial. New England Journal of Medicine 2023;389:514-526.
Cardiovascular and kidney outcomes trial: TRIUMPH-Outcomes, NCT06383390 on ClinicalTrials.gov; currently active, not recruiting, with no results posted at the time of review.
Safety context: MHRA class-wide GLP-1 and dual GLP-1/GIP pancreatitis safety update, 29 January 2026. Retatrutide is not currently a UK-authorised medicine and therefore does not yet have UK-approved product information.
Spotted something out of date or incorrect? Email corrections@thepeptidebrief.co.uk and we will investigate.
This guide is for information purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any treatment.
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This page is for information only and is not medical advice. Always speak to a qualified healthcare professional before starting, stopping or changing treatment.
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