You have probably seen the number: 30% weight loss with retatrutide, Eli Lilly’s next molecule. Before going further, one detail changes how everything else reads. As of 1 August 2026, retatrutide is not approved anywhere in the world. It is not marketed, not available in pharmacies, and no marketing authorisation application has been filed with the European Medicines Agency. This article answers three concrete questions: what retatrutide genuinely adds over tirzepatide, what that gain costs in side effects, and when you could realistically obtain it legally. The answers are less dramatic than the headlines — which is exactly the information you need if you are wondering whether to wait.
What retatrutide is, in one minute
Retatrutide is an investigational triple agonist developed by Eli Lilly under the code LY3437943, given as a once-weekly injection. It acts on three receptors at once: GLP-1, GIP and glucagon. Tirzepatide, the active ingredient in Mounjaro, activates only two of them, GLP-1 and GIP.
That third receptor is what sets the molecule apart. Activating the glucagon receptor increases energy expenditure — the calories your body burns at rest — whereas the other two receptors mainly act on appetite and how quickly the stomach empties. So retatrutide does not only reduce intake; it also acts on output. This additional mechanism explains both the efficacy gain measured in the trials and part of the side effects described below. It is the only pharmacology point worth remembering; the rest is a matter of numbers.
How much weight do people actually lose? The TRIUMPH trial results
At 12 mg, the highest dose tested, retatrutide produced 25.0% weight loss at 80 weeks in the pivotal TRIUMPH-1 trial (2,339 participants), on the treatment-regimen estimand. Across populations, results range from 20.8% to 28.7%. One caveat before reading any of these numbers: they come from topline results announced by the manufacturer. No phase 3 retatrutide trial has been published in full in a peer-reviewed journal to date. Only the phase 2 study has, in the New England Journal of Medicine in 2023, with 24.2% weight loss at 12 mg over 48 weeks.
| Trial | Population | Participants | Duration | Weight loss at 12 mg | Discontinuations due to adverse events |
|---|---|---|---|---|---|
| TRIUMPH-1 | Obesity or overweight, without diabetes | 2,339 | 80 weeks | 25.0% (treatment) / 28.3% (efficacy) | 11.3% |
| TRIUMPH-2 | Obesity with type 2 diabetes | 1,152 | Not stated in the release | 20.8% | 7.7% |
| TRIUMPH-3 | Severe obesity with cardiovascular disease | 1,949 | Not stated in the release | 22.6% | 13.5% |
| TRIUMPH-4 | Obesity with knee osteoarthritis | 445 | 68 weeks | 28.7% | 18.2% |
| TRIUMPH-5 | Head-to-head against tirzepatide | about 800 | about 89 weeks | Results not available | Not available |
TRIUMPH-1: the pivotal trial in 2,339 participants
Over 80 weeks, mean weight loss was 17.6% at 4 mg, 23.7% at 9 mg and 25.0% at 12 mg, against 3.9% on placebo, using the treatment-regimen estimand. On the efficacy estimand, the same arms give 19.0%, 25.9% and 28.3%, against 2.2%. Two secondary results are worth quoting: at 12 mg, 45.3% of participants lost at least 30% of their starting body weight, and 65.3% dropped below a body mass index of 30, meaning below the obesity threshold. If you do not know yours, you can calculate your BMI first — BMI thresholds shape how every one of these trials should be read.
Where the 30% figure everyone quotes actually comes from
The 30.3% figure is real, but it does not describe the main trial. It comes from a subgroup of 532 TRIUMPH-1 participants, all with a BMI of 35 or above, who were already tolerating their dose and were re-escalated to the maximum tolerated dose, measured at 104 weeks rather than 80, on the efficacy estimand. Four restrictive conditions stack up to produce that number.
A word on estimands, because that is where the difference sits. An estimand is the calculation rule chosen to answer a specific question. The treatment-regimen estimand measures weight loss across everyone who started the trial, including those who stopped along the way: it answers “what happens if this drug is prescribed to a population?”. The efficacy estimand measures loss among those who actually stayed on treatment: it answers “what happens in someone who tolerates it?”. The second always gives a higher number. Both are legitimate; they simply answer different questions.
Type 2 diabetes: markedly more modest results (TRIUMPH-2)
Among 1,152 participants living with type 2 diabetes, weight loss at 12 mg fell to 20.8%, against 28.3% in the non-diabetic participants of TRIUMPH-1. HbA1c dropped by up to 1.6 percentage points. This gap is not specific to retatrutide: the same pattern separates SURMOUNT-1 from SURMOUNT-2 for tirzepatide. People with diabetes structurally lose less weight on incretin drugs, whichever molecule is used. If that applies to you, it is a useful reference point — the figures circulating in the media are almost always those of non-diabetic populations.
Cardiovascular disease and knee osteoarthritis (TRIUMPH-3 and TRIUMPH-4)
TRIUMPH-3 enrolled 1,949 people with severe obesity and established cardiovascular disease: 22.6% weight loss at 12 mg. The release also reports cardiovascular data that need careful reading. MACE events — major adverse cardiovascular events, meaning serious cardiovascular incidents — gave a hazard ratio of 0.82 on the five-component endpoint and 1.12 on the three-component endpoint, on small event counts (27 events against 23). The trial was not powered to draw conclusions about cardiovascular risk. These data support neither a claim of benefit nor a claim of harm.
TRIUMPH-4, run in 445 people with obesity and knee osteoarthritis, produced 28.7% weight loss at 12 mg and 26.4% at 9 mg, against 2.1% on placebo, over 68 weeks. The WOMAC pain score fell by 75.8%, and 12% of participants reported no pain at all at 68 weeks. It is the trial that speaks most directly to day-to-day quality of life.
Retatrutide versus Mounjaro: the real gap
On non-comparative data, the gap between retatrutide at 12 mg and tirzepatide at 15 mg is roughly 5 to 7 percentage points. Real and meaningful, but nowhere near the doubling some headlines imply. No trial has directly compared the two molecules to date.
| Retatrutide 12 mg | Tirzepatide 15 mg | Semaglutide 2.4 mg | |
|---|---|---|---|
| Receptors targeted | GLP-1 + GIP + glucagon | GLP-1 + GIP | GLP-1 |
| Weight loss | 28.3% at 80 weeks (TRIUMPH-1, efficacy estimand) | 22.5% at 72 weeks (SURMOUNT-1, efficacy estimand) | Not quoted here, see note |
| Regulatory status | Investigational, approved nowhere | Approved and marketed | Approved and marketed |
| Published evidence | Topline releases; phase 3 unpublished | Published in the NEJM (2022) | — |
Method note. We do not quote figures we have not verified against a primary source, so semaglutide weight loss is left out here; the column exists only to situate the three mechanisms. More importantly, these trials were never compared with one another: populations, durations and protocols differ, so the comparison is indicative at best. The real answer will come from TRIUMPH-5 (NCT06662383), a phase 3 head-to-head study of retatrutide against tirzepatide, with about 800 participants over roughly 89 weeks. Not before.
Side effects: what the data show
The efficacy gain is paid for in tolerability. Gastrointestinal effects are frequent and well known for this drug class; a new signal, absent from phase 2, involves abnormal skin sensations. Discontinuation rates rise with dose.
Gastrointestinal effects
At 12 mg in TRIUMPH-1: nausea in 42.4% of participants, diarrhoea in 32.0%, constipation in 26.1%, vomiting in 25.3%. On placebo, the same effects affected 14.8%, 13.5%, 10.9% and 4.8% respectively. The gap is clear, but the placebo arm is a reminder that some of these symptoms occur regardless of treatment. As with other incretin drugs, they peak during dose escalation.
Dysesthesia: the new signal
Dysesthesia means an abnormal skin sensation: tingling, pins and needles, burning, or heightened sensitivity to touch. These events affected 12.5% of participants at 12 mg in TRIUMPH-1 and up to 20.9% in TRIUMPH-4, against 0.7% to 0.9% on placebo. The signal was absent from the phase 2 study published in 2023. In TRIUMPH-4 these events did not lead to treatment discontinuation. Detailed data and peer-reviewed publication are still awaited, and both financial analysts and clinicians have said they will examine them closely. As things stand, there is no basis either for dismissing this or for alarm.
How many people stop treatment
In TRIUMPH-1, discontinuations due to adverse events affected 4.1% of participants at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, against 4.9% on placebo. The other trials give 7.7% (TRIUMPH-2), 13.5% (TRIUMPH-3) and 18.2% (TRIUMPH-4, an older population with more comorbidities). The trade-off is legible: the most effective dose is also the least well tolerated. The 9 mg arm reached 25.9% weight loss on the efficacy estimand with almost half the discontinuations of the 12 mg arm.
When will retatrutide be available? The real timeline
No launch date has been announced anywhere. The US filing is planned for the first quarter of 2027, and nothing has been filed in Europe. For anyone waiting, the horizon is measured in years, not months.
United States
On 23 July 2026, Eli Lilly announced it would file a Biologics License Application — a BLA, the submission that asks the FDA to approve a biologic medicine — in the first quarter of 2027. That is a slip: the company had previously targeted 2026. FDA review of such an application usually takes ten to twelve months, which places a possible decision in late 2027 or 2028 at the earliest.
Europe and the rest of the world
No marketing authorisation application has been filed with the European Medicines Agency. The only item on the European file is a paediatric investigation plan agreed in September 2024, a mandatory administrative step that says nothing about an imminent filing. After any European approval, national pricing and reimbursement decisions would follow — steps that, for this drug class, are counted in quarters. Since the molecule holds no approval in any country, the same applies everywhere else.
What waiting actually means
Here is the arithmetic. Waiting for retatrutide in August 2026 means giving up three to four years of treatment that exists today, for an expected gain of roughly 5 to 7 percentage points of weight loss, on non-comparative data, with poorer tolerability. If cost is what is holding you back, the question is worth turning around: here is what Mounjaro costs today and how coverage works, for a treatment you could start now rather than in several years. Any decision to start, continue or stop a treatment belongs with your doctor, never with an article.
Can you buy retatrutide today?
No. Any product sold as “retatrutide” today is by definition outside the legal supply chain, because the molecule holds no marketing authorisation in any country. There is no legal source, online or otherwise.
The “research use only” or “not for human consumption” labelling these products carry is a legal wrapper. On 7 April 2026 the FDA published seven warning letters, dated 31 March, addressed to online sellers: the agency took the view that the disclaimer did not exempt them, given that their pages described appetite suppression, weight loss and blood sugar regulation. An earlier round had targeted four sellers in December 2024.
These products circulate under code names worth recognising: “GLP-1-R peptide”, “GLP-3 RT”, “GLP3”. If one of those names is offered to you, what is being sold is unapproved retatrutide. The risks are concrete: manufacturing outside good manufacturing practice, unknown or zero dosing, microbial contamination, toxic substances. European regulators including the EMA and national agencies issued an alert on 9 September 2025, updated on 18 November 2025, about counterfeit GLP-1 analogues sold online — including the fraudulent use of regulator logos on commercial websites.
If you have already bought or injected such a product, tell your doctor. It is not a confession; it is medical information they need, and any adverse effect can be reported to the relevant pharmacovigilance system.
Key takeaways
- Retatrutide is a GLP-1 / GIP / glucagon triple agonist from Eli Lilly, investigational and approved nowhere as of 1 August 2026.
- The headline result of the pivotal TRIUMPH-1 trial is 25.0% weight loss at 12 mg over 80 weeks (treatment estimand), or 28.3% (efficacy estimand), in 2,339 participants.
- The 30.3% figure comes from a subgroup of 532 participants with a BMI of 35 or more, re-escalated to the maximum tolerated dose and followed for 104 weeks. It is not the trial result.
- The gap with tirzepatide is roughly 5 to 7 percentage points, on non-comparative data. TRIUMPH-5 will provide the only direct comparison.
- Tolerability is worse: 11.3% discontinuations for adverse events at 12 mg against 4.9% on placebo, plus a dysesthesia signal (12.5% at 12 mg) absent from phase 2.
- FDA filing announced for the first quarter of 2027, nothing filed with the EMA. An approval decision is unlikely before late 2027 at the earliest.
Frequently asked questions
Is retatrutide better than Mounjaro?
Current data, which are not comparative, suggest a gap of roughly 5 to 7 percentage points of weight loss in favour of retatrutide at its highest dose. No trial has compared the two molecules directly; TRIUMPH-5 is designed to do exactly that. Calling one drug “better” than another has little meaning until that readout exists, particularly since retatrutide is less well tolerated.
When will retatrutide be available?
No date has been announced. Eli Lilly plans to file with the FDA in the first quarter of 2027, and FDA review of such an application typically takes ten to twelve months, putting a possible decision in late 2027 or 2028 at the earliest. In Europe, no marketing authorisation application has been filed at all, so European availability sits several years further out.
Does retatrutide cause 30% weight loss?
Not in the trials’ headline result. The 30.3% figure corresponds to a subgroup of 532 TRIUMPH-1 participants with a BMI of at least 35, who were already tolerating their dose, were re-escalated to the maximum tolerated dose and were followed for 104 weeks, on the efficacy estimand. The trial’s primary result is 25.0% at 80 weeks.
Should I stop my current treatment to wait for retatrutide?
That question belongs with your doctor, and only with your doctor. What this article can contribute are the terms of the calculation: an estimated three to four year wait for a gain of roughly 5 to 7 percentage points, with less favourable tolerability and phase 3 data still unpublished in full. Interrupting an ongoing treatment to wait for a molecule that has not even been filed in Europe is not a minor decision.
Medical disclaimer. This article is strictly informational and does not replace medical advice. Retatrutide is an investigational molecule: it is not approved, marketed or available in pharmacies in any country as of 1 August 2026, and no legal source exists to obtain it. The doses mentioned correspond to clinical trial arms and are in no way dosing guidance. Any decision to start, change or stop a treatment should be made with a healthcare professional. Information current as of 1 August 2026; this page is reviewed quarterly.