Key takeaways
- Investigational only: retatrutide is not licensed in the UK or the US and is not available as a medicine outside an authorised clinical trial.
- Three hormone targets: it activates GLP-1, GIP and glucagon receptors, which is why it is called a triple agonist.
- Strong Phase 3 results: in TRIUMPH-1, average weight loss on 12 mg was 28.3% over 80 weeks on Lilly's efficacy estimand and 25.0% on the treatment-regimen estimand, versus 3.9% with placebo.
- Timeline unclear: Lilly plans to submit to the FDA in the first quarter of 2027. No MHRA submission or UK launch date has been confirmed.
- Licensed options exist now: Mounjaro, Wegovy and other MHRA-licensed treatments can be prescribed today after a clinical review.
What is retatrutide and how does the "Triple-G" mechanism work?
Existing weight loss medicines act through several pathways, including effects on appetite, satiety and food intake. Retatrutide is designed to combine these effects with glucagon receptor activity, which may also influence energy expenditure and lipid metabolism.
It does this by activating three separate metabolic hormone receptors at once:
- GLP-1 (glucagon-like peptide-1): delays stomach emptying and acts on satiety centres in the brain, reducing hunger and quietening persistent food noise.
- GIP (glucose-dependent insulinotropic polypeptide): works alongside GLP-1 to enhance the body's natural insulin response to meals, improve blood sugar control and influence fat storage.
- Glucagon (the third target): glucagon receptor activation influences hepatic glucose and lipid metabolism and may contribute to increased energy expenditure. Combined with GIP and GLP-1 receptor agonism, this is being investigated for its potential to improve weight and metabolic outcomes.
By activating all three receptors, retatrutide is intended to reduce food intake while also influencing metabolic pathways involved in energy balance.
What do the clinical trials show?
Retatrutide has been studied in Lilly's Phase 3 TRIUMPH and TRANSCEND programmes. Some findings have been published in peer-reviewed journals, while others currently remain available as company-reported topline or conference data.
Trial results may be reported using different statistical approaches, known as estimands. In simple terms, the efficacy estimand estimates the effect if participants remained on treatment as planned, whereas the treatment-regimen estimand reflects the overall trial experience, including treatment discontinuation and other events. For TRIUMPH-1 at 80 weeks, mean weight loss with 12 mg was 28.3% using Lilly's efficacy estimand and 25.0% using the peer-reviewed treatment-regimen estimand, compared with 3.9% with placebo.
The findings represent some of the highest average reductions in body weight documented in clinical obesity trials:
| Patient group | Clinical trial | Highest dose (12 mg) result | Additional health markers |
|---|
| Adults with obesity (without diabetes) | TRIUMPH-1 | 28.3% average weight loss over 80 weeks using Lilly's efficacy estimand; 25.0% using the peer-reviewed treatment-regimen estimand (3.9% with placebo) | 45.3% of participants lost 30% or more of their total weight; average waist circumference dropped by up to 9.5 inches |
|---|
| Adults with type 2 diabetes | TRIUMPH-2 | 20.8% average weight loss over 80 weeks using Lilly's efficacy estimand; 18.8% using the treatment-regimen estimand | Up to 40% reached normal, non-diabetic blood sugar levels without additional medication |
|---|
| Cardiovascular risk | TRIUMPH-3 | 22.6% average weight loss over 80 weeks | Notable reductions in systolic and diastolic blood pressure, along with substantial drops in triglycerides |
|---|
| Knee osteoarthritis | TRIUMPH-4 | 28.7% average weight loss over 68 weeks in Lilly's efficacy-estimand analysis | Knee osteoarthritis pain also improved substantially, but the trial does not establish that the entire improvement was directly caused by reduced joint loading |
|---|
Results from different trials involve different populations, so they cannot be compared directly with each other or with trials of other medicines.
Other key clinical findings
- Liver fat reduction: in a Phase 2 substudy of 98 participants with MASLD and at least 10% liver fat, mean relative liver-fat reduction at 24 weeks was 81.4% with 8 mg and 82.4% with 12 mg. Liver fat fell below 5% in 79% and 86% of participants, respectively. These imaging findings do not by themselves demonstrate resolution of MASLD, MASH or liver fibrosis.
- Sleep apnoea: in the TRIUMPH-1 obstructive sleep apnoea substudy, retatrutide reduced the apnoea-hypopnoea index by up to 36.1 events per hour, equivalent to a 60.6% reduction in Lilly's reported analysis. The available results do not establish that changes in neck and visceral fat were the sole cause of this improvement.
Side effects and safety considerations
Because glucagon receptor activity may influence energy expenditure and lipid metabolism, monitoring tolerability remains an important focus of ongoing retatrutide research:
- Digestive symptoms: as with current incretin therapies, mild-to-moderate nausea, diarrhoea, vomiting and constipation are the most frequent side effects, particularly during dose increases.
- Resting heart rate: dose-dependent increases in heart rate have been observed in clinical trials. In the Phase 2 obesity trial, heart rate peaked at 24 weeks and then declined, although it remained above baseline at 48 weeks in some dose groups. Longer-term cardiovascular safety continues to be evaluated.
- Sensory changes and fatigue: clinical trial reports have noted transient skin sensitivity (dysaesthesia), headaches and fatigue during initial titration.
When will retatrutide be available in the UK?
Retatrutide is currently an unapproved investigational medicine. It is not yet licensed by the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK or the FDA in the United States.
- Current stage: Phase 3 trial series completion and global data compilation.
- Regulatory submissions: Lilly has stated that it plans to submit a Biologics License Application for retatrutide to the FDA in the first quarter of 2027. A corresponding MHRA submission date has not been confirmed.
- Expected UK timeline: no confirmed UK approval or commercial availability date has been announced. Any UK launch would depend on submission to the MHRA, a favourable regulatory decision and subsequent commercial arrangements.
Important safety notice: retatrutide is not approved for routine clinical use in the UK and is not available as a licensed medicine. Products sold online as retatrutide have not been assessed through the UK medicines licensing process and may present serious quality and safety risks. Patients should not obtain or use such products outside an authorised clinical trial.
Weight management treatments available at PrivateDoc today
While retatrutide works its way through clinical trials and regulatory review, MHRA-licensed medical treatments are available now. At PrivateDoc, our Care Quality Commission (CQC) regulated clinic provides doctor-led weight management programmes tailored to your medical history and lifestyle:
- Dual-action injections (Mounjaro / tirzepatide): targets GLP-1 and GIP receptors, with average weight loss of around 20% at the highest dose in clinical trials.
- GLP-1 injections (Wegovy / semaglutide): targets GLP-1 to quieten food noise, promote satiety and support steady weight loss.
- Daily oral options (Wegovy pill, Mysimba, orlistat): needle-free alternatives for people seeking structured appetite control or fat-absorption inhibition.
- Ongoing clinical oversight: prescriptions are reviewed by GMC-registered doctors and registered prescribers, supported by our patient app and optional at-home metabolic blood testing.
Not sure how retatrutide compares with what you can start today? Read our guide to retatrutide vs Mounjaro.
Get retatrutide updates from PrivateDoc
Want to stay informed about clinical trial milestones, MHRA regulatory updates and any future change in the availability of retatrutide in the UK? Join the PrivateDoc retatrutide updates list to receive:
- Timely updates on Phase 3 trial readouts and safety publications.
- Verified news on UK licensing and MHRA decisions.
- A notification from us if this changes and retatrutide becomes available through a UK-licensed route.
Joining the list is not a request for treatment and does not reserve a prescription. If you would like to start your weight loss journey today with existing, licensed treatments, visit our weight loss page to complete your free online consultation.
Disclaimer: This article is for general information only and does not replace personalised medical advice. Retatrutide is an investigational medicine and is not licensed in the UK. Always speak to a registered healthcare professional about your own circumstances.
