Retatrutide: The Next-Generation Weight Loss Drug Explained
Medically reviewed by Puja Vyas
30.3% of body weight at two years - That’s Retatrutide for you.
Retatrutide is a new weight loss drug that is generating serious attention in clinical and scientific circles and for good reason. Developed by Eli Lilly, it has just produced the highest weight loss results ever recorded for any anti-obesity medication in a Phase 3 clinical trial: 30.3% of body weight at two years.
What Is Retatrutide?
Retatrutide is a once-weekly injectable drug developed by Eli Lilly, the same company that developed Mounjaro. It falls under the category of medicines called triple hormone receptor agonists, or ‘triple agonists’ or ‘triple incretin agonists’.
We know these jargon sounds overwhelming. So, here a simple explanation for it -
How Does It Work? GIP, GLP-1 and Glucagon Triple Agonism Explained
Wegovy targets one hormone receptor (GLP-1). Mounjaro targets two (GLP-1 and GIP). Retatrutide targets and works on three:
The third one, glucagon, component is what sets retatrutide apart from everything currently on the market. It is a key reason why retatrutide is producing weight loss results that exceed both semaglutide and tirzepatide in trials.
Retatrutide for Weight Loss: What Do the Clinical Trials Show?
The clinical evidence for retatrutide weight loss is nothing less than extraordinary. We’ve tracked the data across Phase 2 and the two Phase 3 trials with published results so far.
The Phase 2 trial, published in the NEJM in June 2023
- 48-week randomised controlled trial
- 338 adults with obesity or overweight without type 2 diabetes.
- Tested against placebo.
Participants on the 12mg dose lost an average of 24.2% of their body weight over 48 weeks. 100% of those on 12mg lost at least 5% of body weight, and 83% lost at least 15%.
The Phase 3 trial, December 2025 (Eli Lilly published topline results from TRIUMPH-4) showed 28.7% weight loss at 68 weeks.
Then, on 21 May 2026, TRIUMPH-1, the pivotal obesity trial with 2,339 participants reported an average of 30.3% weight loss in 104 weeks at the 12mg dose.
Retatrutide Dosage: Doses Used in Clinical Trials
First and foremost - Retatrutide is not approved for prescription in the UK. The dosage information below comes exclusively from published clinical trial protocols and is for informational purposes only.
In both Phase 2 and Phase 3 trials, retatrutide was administered as a once-weekly subcutaneous injection, starting at a low dose and escalating gradually every four weeks.
This approach is the same as what you would have seen with Wegovy and Mounjaro - ‘start low, go slow’. The gradual escalation reduces the intensity of gastrointestinal side effects during the adjustment period.
It has a half-life of approximately six days. This means that while it would take around 30 days to fully clear from the body, it would still be appropriate for a once-weekly dose.
Dosage Chart: Starting Dose and Escalation Schedule
Retatrutide Side Effects and Safety: What the Research Shows
The side effects in the case of Retatrutide are similar to what clinicians have seen with Wegovy and Mounjaro. There was some uniqueness to it because of the new third mechanism, glucagon, that no currently approved weight loss drug includes.
In the Phase 3 TRIUMPH-4 trial, the most common side effects at the 12mg dose were:
- Nausea: 43.2% (vs 10.7% on placebo)
- Diarrhoea: 33.1% (vs 13.4% on placebo)
- Vomiting: 20.9% (vs 0% on placebo)
- Constipation: 25.0% (vs 8.7% on placebo)
The majority of these side effects were seen to be moderate, occurring mainly during dose escalation periods, and diminished once participants stabilised at their maintenance dose.
Till now everything is similar to the already existing medications. But as we stated above, there were some unique ones to Retatrutide -
Risks and Expert Warnings
The most clinically significant new safety signal identified in Phase 3 is dysesthesia, abnormal skin sensations including tingling, burning, numbness, or unusual sensitivity to touch.
This was reported in 20.9% of participants on the 12mg dose in TRIUMPH-4, compared to 0.7% on placebo. Most cases, however, were mild and did not lead to treatment discontinuation.
Other effects that we can see in the trial data are -
- Heart rate increase - An average increase of 5–10 beats per minute was seen at the 12mg dose, peaking around week 24 and declining thereafter. This is higher than that seen with tirzepatide (+2–3 bpm) or semaglutide (+3–4 bpm). Again, no increase in serious cardiovascular events was observed in Phase 2.
- Liver enzyme elevations - A temporary ALT/AST increases in a minority of participants was seen. This was usually tied to dose escalation steps and not associated with liver damage signals
- Discontinuation rates - Diabetes trial saw a 5.1% discontinuation rate in TRANSCEND-T2D-1 and 18.2% in TRIUMPH-4 at 12mg. While these are higher than comparable trials for semaglutide or tirzepatide, a direct comparison is difficult since the trials were designed differenyly.
Retatrutide vs Tirzepatide vs Semaglutide: How Does It Compare?
Yes, we know that 30.3% vs 22.5% vs 20.7%, the difference is significant. But there are other important factors to consider. The retatrutide trial was 104-week one against 72-weeks for Mounjaro and Wegovy. Longer trials tend to produce higher results as weight loss continues to accumulate. We do not have direct head-to-head comparison data yet.
Can You Buy Retatrutide in the UK Right Now?
No. Retatrutide has not been approved by the MHRA and cannot legally be prescribed in the UK outside of a clinical trial.
As of May 2026, the TRIUMPH Phase 3 programme is still ongoing. Eli Lilly is expected to file for FDA approval in 2026, following the TRIUMPH-1 results. European Medicines Agency and MHRA authorisation, would typically follow FDA approval by twelve months or more.
If all regulatory steps go smoothly, you can expect Retatrutide to be legally available in the UK in the later part of 2027.
We may see seven additional Phase 3 TRIUMPH trials results throughout 2026, including studies on maintenance dosing strategies and cardiovascular outcomes.
Risks of Buying Retatrutide Peptides Online
‘Retatrutide for sale’ or ‘Reta Peptides’ are being advertised on platforms like TikTok, Telegram, or ‘research chemical’ websites. We know that these results are difficult to ignore. But remember that these are very potent medications. Administering them without clinical supervision can lead to severe, even fatal, harm to your body.
Under the Human Medicines Regulations 2012, any product presented as treating or preventing disease becomes a ‘medicinal product’ requiring MHRA authorisation, regardless of the disclaimer on the label.
Purchasing from unauthorised sellers can leave you exposed to unknown ingredients, incorrect dosing, bacterial contamination, and most importantly, complete absence of any medical assistance if something goes wrong.
Phase 3 Clinical Trials: Latest News and UK Approval Timeline
The TRIUMPH programme is Eli Lilly’s Phase 3 clinical trial plan for retatrutide, covering multiple conditions and patient populations. Here’s what we know as of May 2026:
- TRIUMPH-4 (December 2025): Retatrutide 12mg produced 28.7% average weight loss at 68 weeks in adults with obesity and knee osteoarthritis. 75.8% reduction in knee pain scores.
- TRIUMPH-1 (May 2026): With 2,339 participants in 80–104 weeks showed 28.3% at 80 weeks and 30.3% at 104 weeks at the 12mg dose. The trial included all three doses (4mg, 9mg, 12mg).
- Seven further TRIUMPH trials: Expected to report throughout 2026, covering maintenance dosing, cardiovascular outcomes, and other populations.
Retatrutide received Fast Track Designation from the FDA, which may accelerate the review process in the United States. Eli Lilly is expected to file for FDA approval following TRIUMPH-1. After that we can expect MHRA approval in the UK.
We will update this article as further TRIUMPH results are published.
Summary
Retatrutide can be a game changer in the weight loss medication zone. The current results are more promising than any other similar medication. However, it is not currently approved by the FDA and may take another 1-2 years for the same.
The only wise thing to do here is to wait for the official approvals and then consult your GP/provider for the same. While trials show specific results, they always vary from person to person. It is important for your clinician to examine your body and your needs before prescribing anything.
Frequently Asked Questions About Retatrutide
Is Retatrutide FDA or MHRA Approved?
No. As of May 2026, retatrutide has not received approval from the FDA, the MHRA, or the European Medicines Agency. It remains an investigational drug in Phase 3 clinical trials. Eli Lilly is expected to submit for FDA approval in 2026 following TRIUMPH-1.
Will Retatrutide Come as a Pen, and How Much Will It Cost?
Eli Lilly has not confirmed the final delivery format for Retatrutide. Given that Mounjaro is delivered via a KwikPen injector, a similar format is likely, but this is only a guess. UK pricing has not been disclosed. While Retatrutide’s greater efficacy could support a higher list price, NICE appraisal and NHS negotiation processes would ultimately determine what UK patients pay through the NHS.
When will Retatrutide be available?
Retatrutude has received a Fast Track Designation from the FDA, which can accelerate the review process for it. If everything goes smoothly, MHRA approval should follow and we can expect it to be available by the end of 2027 or early 2028.
But that doesn’t mean that you journey must wait till then.
If you’re looking to start or improve your weight management journey right now, the evidence-based options are Mounjaro and Wegovy, both of which are available through SheMed’s clinically led programme.
Sources & Further Reading
- Jastreboff AM et al. — Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. NEJM, 2023
- Sources: Jastreboff et al., NEJM 2023 (Phase 2); Eli Lilly press releases, December 2025 and May 2026 (Phase 3 TRIUMPH-4 and TRIUMPH-1); AJMC reporting on TRIUMPH-1
- PMC12190491 — Efficacy and Safety of Retatrutide: Systematic Review and Meta-analysis
- ClinicalTrials.gov — NCT05929066: TRIUMPH Phase 3 Programme
- Eli Lilly — What to Know About Retatrutide
- AJMC — Retatrutide Achieves Up to 30.3% Average Weight Loss in Phase 3 TRIUMPH-1 Trial (May 2026)
- MHRA — Medicines and Healthcare Products Regulatory Agency (GOV.UK)
- STV News — The Peptide Boom: Call for Review of Legal Loophole (March 2026)
Jastreboff et al., NEJM 2023; ClinicalTrials.gov — NCT05929066 (TRIUMPH Phase 3 Programme)
The content on the SheMed blog is provided for general informational and educational purposes only. While SheMed provides professional weight loss services and strives to ensure the information shared is accurate and up to date, we make no representations or guarantees as to its accuracy, completeness, or timeliness. This content should not be taken as personal medical advice or a substitute for consultation with a qualified healthcare provider. Always speak with your doctor or licensed medical professional about your individual health or medical needs before starting any new treatment or programme. Never disregard or delay seeking professional medical advice because of something you have read on this site. SheMed is not responsible for any actions you may take based on the information provided in this blog.
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