Jump to: What is the average weight loss on retatrutide? | Is retatrutide the same as tirzepatide? | Is retatrutide the same as semaglutide? | Retatrutide side effects and safety signals | When will retatrutide be available? | Second Nature’s medication programmes | References
Retatrutide is a triple-action weight-loss injection made by Eli Lilly. In Phase 3 trials, it’s delivered up to 28.7% body-weight loss at 68 weeks at the 12 mg dose, alongside reductions in knee osteoarthritis pain.1 It isn’t yet approved in the UK or the US.
Important safety information: Retatrutide is an investigational medicine. It isn’t licensed by the MHRA in the UK and you can’t legally buy it from UK pharmacies in May 2026. This article is for informational purposes only. Always consult your healthcare provider before starting or changing any weight-loss treatment.
Retatrutide is a ‘triple hormone receptor agonist’. This means it mimics three hormones in the body that affect appetite, blood sugar levels, and how we burn fat for energy.
It’s expected to be approved for adults living with obesity and type 2 diabetes, if it passes its remaining Phase 3 trials. Eli Lilly has said it’s targeting an FDA submission in late 2026.2
The three hormones that retatrutide mimics are:
- GLP-1: Lowers appetite and blood sugar levels
- GIP: Lowers appetite and blood sugar levels
- Glucagon: Promotes fat breakdown for energy and helps prevent low blood sugar levels
The triple action means retatrutide has a substantial effect on appetite and blood sugar. In head-to-head data so far, it’s produced greater weight loss than semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro).
What is the average weight loss on retatrutide?
The most recent published data is from TRIUMPH-4, a Phase 3 trial of 445 adults with obesity and knee osteoarthritis. Over 68 weeks, the 12 mg dose led to 28.7% body-weight loss, the 9 mg dose led to 26.4%, and placebo led to 2.1%.1
The trial also reported clinically meaningful reductions in knee pain. The 12 mg group saw a 4.4-point drop on the WOMAC pain scale, and roughly 1 in 8 participants on retatrutide became completely free of knee pain, compared with 1 in 24 on placebo.3
In TRANSCEND-T2D-1, Lilly’s first Phase 3 trial in adults with type 2 diabetes (n=537, 40 weeks), retatrutide produced 16.8% weight loss at the 12 mg dose, alongside a 2.0% reduction in HbA1c. Detailed findings are due at the American Diabetes Association Scientific Sessions in June 2026.2
These figures build on the original Phase 2 trial published in the New England Journal of Medicine in 2023, which reported 24% weight loss after 48 weeks at the highest dose in 338 participants.4 Phase 3 confirms the earlier findings and extends them to longer follow-up.
Losing and maintaining more than 10% of body weight is associated with significant reductions in obesity-related complications, including hypertension, type 2 diabetes, and heart disease.5
Three more Phase 3 trials are expected to read out across 2026:
- TRIUMPH-1 (general obesity, 80 weeks): readout expected Q2-Q3 2026. This is the trial that anchors Lilly’s new drug application for weight management.
- TRIUMPH-2 (obesity with type 2 diabetes, around 1,400 adults): readout expected Q3-Q4 2026.
- TRIUMPH-3 (obesity with obstructive sleep apnoea, around 600 adults): readout expected late 2026.6
Is retatrutide the same as tirzepatide (Mounjaro)?
Retatrutide and tirzepatide are different drugs with different chemical compositions. Retatrutide mimics three hormones to support weight loss; tirzepatide mimics two.
In the trials we have so far, retatrutide has produced greater weight loss. The 12 mg dose in TRIUMPH-4 led to 28.7% loss over 68 weeks, while tirzepatide in the SURMOUNT-1 trial produced around 22.5% over 72 weeks.1
Direct head-to-head trials between the two drugs haven’t yet been completed, so cross-trial comparisons should be read with care. Different trial populations and durations affect the headline numbers.
For most people, losing more than 20% of body weight in a year is enough to deliver meaningful health improvements. Not everyone needs to lose more than this for the long-term health benefits.
Is retatrutide the same as Ozempic (semaglutide)?
Retatrutide and Ozempic (semaglutide) are different drugs with different chemical compositions.
While retatrutide mimics three hormones, semaglutide only mimics one (GLP-1).
Retatrutide also produces greater weight loss. Trial data on Ozempic shows an average weight loss of about 6 kg over 40 weeks at the 1 mg dose used for type 2 diabetes.7 The 2.4 mg dose used in Wegovy produces around 15% over 68 weeks.
In contrast, the 12 mg dose of retatrutide produced about 32 kg of weight loss in TRIUMPH-4 over 68 weeks.
Ozempic isn’t approved for weight loss in the UK and can only be prescribed for people living with type 2 diabetes. Retatrutide isn’t approved in the UK at all, but it’s expected to be licensed for both weight loss and type 2 diabetes once trials are complete.
Retatrutide side effects and safety signals
The most common side effects in the Phase 3 trials are gastrointestinal: nausea, vomiting, diarrhoea, and constipation. In TRIUMPH-4, nausea affected around 43% of participants on 12 mg, vomiting 21%, and diarrhoea 33%. Most cases were mild to moderate and clustered during the dose-escalation period.3
A new safety signal flagged in TRIUMPH-4 is dysesthesia, an abnormal skin sensation people describe as burning, tingling, or ‘pins and needles’. It affected 8.8% on 9 mg and 20.9% on 12 mg, compared with 0.7% on placebo. Most cases were mild.3
The Phase 2 trial reported small heart rate increases (around 6.7 beats per minute at 12 mg), peaking around week 24 and then declining.4 Cardiac arrhythmias affected 2-11% of participants on retatrutide vs 2% on placebo, but none were serious. No increase in major cardiovascular events has been reported.
Discontinuation rates due to side effects were 18.2% on 12 mg, 12.2% on 9 mg, and 4% on placebo in TRIUMPH-4.3
Long-term cardiovascular outcomes data isn’t yet available. Lilly hasn’t yet completed a dedicated cardiovascular outcomes trial for retatrutide.
When will retatrutide be available?
Retatrutide isn’t approved by the MHRA in the UK or the FDA in the US in May 2026. The realistic timeline is several years away.
Eli Lilly has said it’s targeting a new drug application (NDA) submission to the FDA in late 2026, after the TRIUMPH-1 readout.2 Based on standard FDA review timelines, US approval is plausible from late 2026 to mid-2027.
UK approval typically lags US approval by 6-18 months. So MHRA approval is most realistic in late 2027 to mid-2028. NHS access through a NICE technology appraisal usually adds another 12-18 months on top, putting NHS availability at 2029 at the earliest.
For context, here’s how the most recent GLP-1 weight-loss drugs reached UK patients:
- Wegovy (semaglutide): MHRA approval September 2021, NICE TA875 issued March 2023.8
- Mounjaro (tirzepatide): MHRA approval November 2023, NICE TA1026 issued December 2024.9
If retatrutide passes the remaining TRIUMPH trials and is licensed by the MHRA, Second Nature plans to assess it as an option alongside our existing Wegovy and Mounjaro programmes.
Some online vendors sell retatrutide as a ‘research chemical’ or ‘peptide for research use only’. These products aren’t regulated by the MHRA and can’t be verified for purity or correct dosing. The MHRA raided a UK facility producing counterfeit retatrutide and tirzepatide in December 2025.
If you’re considering weight-loss medication now, talk to your GP about MHRA-approved options like Mounjaro and Wegovy.
We believe there’s no point in taking medications without changing habits
Weight-loss injections are designed as additional tools for healthy lifestyle change and shouldn’t be considered lifelong medications.
Instead, they’re best used to help kickstart weight loss while you focus on building new, healthy habits.
Consider how antidepressants are used for people living with depression. They’re not designed to cure the condition. They’re designed to allow room for therapy to address the condition’s underlying cause.
Mounjaro and Wegovy work in a similar way for weight management. These medications can help silence food-related thoughts and give you a boost of confidence with more immediate weight-loss results.
This buys you time and headspace to understand why your body may have struggled to lose weight previously, and to build long-term healthy habits.
Our medication programmes focus on calming food noise, lowering cravings, and helping you build healthier habits to keep the weight off for good.
The ultimate goal is to make losing weight feel second nature.
Second Nature’s medication programme
Second Nature has worked with the NHS for over 6 years, providing weight-loss programmes across the UK. We currently provide Mounjaro as part of our Mounjaro weight-loss programme.
Our 12-month outcomes were published in JMIR Formative Research in 2025: active subscribers achieved 19.1% average weight loss at 12 months, with 77.7% achieving 10% or more weight loss.10
While our medication programme is private and not currently used by the NHS, we’ve built it around scientific evidence, patient safety, and data security. We hope our 6+ years of NHS partnership and our published outcomes give you peace of mind to give us a try.
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- Eli Lilly. (2025). Lilly’s triple agonist retatrutide delivered weight loss of an average of 28.7% in TRIUMPH-4.
- Eli Lilly. (2026). Investor communications on TRANSCEND-T2D-1 and TRIUMPH programme timing. See Lilly investor relations.
- Healio. (2025). Retatrutide confers up to 28.7% weight loss, reduction in knee osteoarthritis pain. Endocrine Today.
- Jastreboff, A. M., Kaplan, L. M., Frías, J. P., et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity – A Phase 2 Trial. New England Journal of Medicine, 389(6), 514-526.
- Wilding, J. P. H., Jacob, S. (2021). Cardiovascular outcome trials in obesity. The Lancet.
- Giblin, E. M., et al. (2026). The TRIUMPH Phase 3 Programme: design of the retatrutide registrational trials. Diabetes, Obesity and Metabolism.
- Wilding, J. P. H., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384, 989-1002.
- National Institute for Health and Care Excellence. (2023). TA875: Semaglutide for managing overweight and obesity.
- National Institute for Health and Care Excellence. (2024). TA1026: Tirzepatide for managing overweight and obesity.
- Richards, R., et al. (2025). A Remotely Delivered GLP-1RA-Supported Specialist Weight Management Program in Adults Living With Obesity: Retrospective Service Evaluation. JMIR Formative Research.
