The short version: the number everyone is quoting — 28.3% — is not the number in the paper. That figure is the efficacy estimand: what happened to people who stayed on the drug. When TRIUMPH-1 was finally published in the New England Journal of Medicine on 29 September 2026, the treatment-regimen estimand — everyone randomised, whether they stuck with it or not — came in at 25.0%.

And 30.3%, the figure doing the rounds in headlines, describes 532 people who started with a BMI of 35 or more, completed 80 weeks, and tolerated the top dose. It is a thrice-selected subgroup, not the trial.

Both of those are still extraordinary. A quarter of your body weight, from an injection, is bariatric-surgery territory and nothing else has come close. But three things are worth knowing before you get excited: TRIUMPH-1 published no body-composition data at all, no heart-rate numbers have been released for a drug whose third mechanism is known to raise it, and the first hard-outcome data is due in 2029.

Meanwhile in Australia, six people in Victoria have been hospitalised with liver injury and one man tore his oesophagus — all from products bought online labelled "retatrutide." When one vial was analysed, it contained no retatrutide at all.

What retatrutide is

Retatrutide (formerly LY3437943) is Eli Lilly's triple agonist. Where semaglutide hits one receptor (GLP-1) and tirzepatide hits two (GIP and GLP-1), retatrutide adds a third: glucagon.

That third mechanism is the interesting part and the risky part. Glucagon receptor agonism increases energy expenditure — it makes you burn more, rather than only eat less. It is also the reason this drug needs closer safety scrutiny than its predecessors, because glucagon agonism raises heart rate.

Hold that thought. It matters later.

What TRIUMPH-1 actually was

**Jastreboff A, et al. "Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity." New England Journal of Medicine, published 29 September 2026. DOI 10.1056/NEJMoa2604169.**

• NCT05929066. Phase 3, multicentre, randomised, double-blind, placebo-controlled
• n = 2,339, randomised 1:1:1:1 to retatrutide 4 mg / 9 mg / 12 mg / placebo, once weekly subcutaneous
• 80 weeks, with a pre-specified blinded extension to 104 weeks in a subgroup
• Adults with obesity, or overweight plus at least one weight-related comorbidity, without type 2 diabetes
• Primary endpoint: percent change in body weight at week 80
• Funder: Eli Lilly and Company, which designed, funded, ran and analysed it

One design feature that doesn't get mentioned enough: TRIUMPH-1 is a "basket" trial with nested sub-protocols for obstructive sleep apnoea and knee osteoarthritis, with type I error controlled across the family. Those results aren't post-hoc fishing — they were planned.

On the authorship. Lead author Ania Jastreboff directs the Yale Obesity Research Center and is a long-standing Lilly investigator and consultant. She was also lead author on the Phase 2 retatrutide trial and on SURMOUNT-1, the pivotal tirzepatide trial — also Lilly. This is a company trial reported by company-affiliated investigators. That is normal in this field and it is not an accusation; it is context you should carry into every number below.

The result, and why there are two of them

An estimand is the precise question a trial answers. Two legitimate ones were pre-specified here, and they give different answers.

The efficacy estimand asks: what happens to someone who takes the drug as directed and doesn't start another weight-loss treatment? The treatment-regimen estimand asks: what happens to everyone who was randomised, including the people who stopped, lapsed or added something else?

The second is the one that describes what a population of real patients gets. The first is the one that went in the press release.

Neither is dishonest. Both were planned. But for four months, between the May press release and the September publication, the only figure in circulation was the flattering one — and it is still the figure in most of the coverage.

Use 25.0% as your number.

We have not been able to read the full NEJM paper — it sits behind a paywall — so the figures above come from the May Lilly release and from reporting of the published paper. The 95% confidence intervals for every endpoint are in that paper and we have not seen them. We are quoting p-values and point estimates only, and flagging that as a gap rather than printing intervals we haven't verified.

The 30.3% figure, precisely

The 104-week extension enrolled n = 532 — a pre-specified, blinded continuation. To be in it, you had to:

1. Have had a baseline BMI of 35 or above, and
2. Have completed the 80-week study, and
3. Have tolerated your assigned dose

Those 532 people reached −30.3% on 12 mg. That is a real result for a real group. It is not "retatrutide produces 30% weight loss," because the trial selected three times over for people who both respond well and stay on it. Reporting on this figure — including from outlets that should know better — has mostly dropped the qualifiers.

One more thing the extension didn't report: discontinuation data for that cohort.

How many people lost a lot of weight

At 80 weeks, efficacy estimand (the press-release numbers; the treatment-regimen versions weren't published):

Nearly two thirds of people on the top dose lost a quarter of themselves. That is the genuinely remarkable part of this trial and it shouldn't get lost in the caveats.

The ≥5%, ≥10%, ≥15% and ≥20% thresholds weren't in the press release. They're presumably in the paper.

Waist, and the two nested trials

Waist circumference, from a baseline of 118.3 cm: −16.3 cm / −21.8 cm / −24.1 cm versus −3.6 cm on placebo.

Knee osteoarthritis (WOMAC pain subscale, baseline around 6): retatrutide −3.2 to −3.6 versus placebo −1.9; p<0.001.

Obstructive sleep apnoea (apnoea-hypopnoea index, baseline 58.6 events/hour): retatrutide −22.9 to −34.3 events/hour versus −9.9 on placebo; p<0.001.

Read that OSA baseline carefully. An AHI of 58.6 is severe sleep apnoea. A 34-point reduction is a large, clinically real improvement — and it still leaves the average patient in the moderate range. This is a meaningful benefit, not a cure.

Cardiometabolic markers — non-HDL cholesterol, triglycerides, systolic blood pressure, hsCRP — were reported as improved. Lilly released no magnitudes, no confidence intervals and no p-values for any of them. Direction only.

The three things the trial didn't tell you

1. No body composition. None.

At 25–30% weight loss, the single most important question is: what did you lose?

TRIUMPH-1 contains no DXA data, no lean mass figure, no fat mass figure. We checked the Lilly release and the coverage in HCPlive, Pharmacy Times, Healio, AJMC and Scientific American. Not one reports body composition. Waist circumference is the only body-shape measure in the whole package.

What exists comes from a Phase 2 substudy in people with type 2 diabetes (Lancet Diabetes & Endocrinology 2025, n=189, Lilly-funded, doses 0.5–12 mg plus dulaglutide and placebo comparators):

• Fat mass: −26.1% at 8 mg, −23.2% at 12 mg, versus −4.5% placebo
• Lean mass: down as much as −12.5% at 8 mg
• Fat loss index — the share of weight lost that was fat: 62.0% to 69.3%

So roughly 31–38% of the weight lost was not fat. It was lean mass: muscle, organ tissue, water, glycogen.

Here is the honest reading, and it cuts both ways. That ratio is broadly in line with other incretin drugs and with diet-induced weight loss — retatrutide does not appear to be unusually catabolic. Weight loss by any method takes 20–30% from lean tissue, and some of what DXA calls "lean mass" is water and glycogen rather than muscle.

But a normal ratio applied to an abnormal total is not a normal outcome. Losing 12.5% of your lean mass is a different proposition from losing 5%. For someone who is 68 and already close to sarcopenia, that is the question that decides whether this drug helps or harms — and the Phase 3 trial in 2,339 people did not measure it.

(Those figures are reported as standard errors, not confidence intervals, and reach us through secondary coverage because the Lancet paper is paywalled.)

2. No heart rate. For a glucagon agonist.

This one is harder to defend.

Glucagon receptor agonism raises heart rate. It is the best-understood mechanistic reason to watch a triple agonist more closely than a GLP-1. And:

• Lilly's 21 May 2026 release: no heart rate.
• Lilly's 23 July 2026 release: no heart rate.
• Lilly's 29 September 2026 release: no heart rate.
• Healio, Pharmacy Times, HCPlive, AJMC: no heart rate.

We searched specifically for the mean change in beats per minute per arm and could not find it in any legitimate source. We could not confirm whether the dose-dependent rise seen in Phase 2 plateaued or persisted. Every search result offering a specific bpm figure was a peptide-vendor or supplement site, and we are not citing those.

The data is presumably in the NEJM supplementary appendix. But for four months the company published three releases on this drug, and none of them contained the one safety number its mechanism most obviously demands. That is a fair criticism and it is worth making.

3. No hard outcomes until 2029

There is no mortality data, no heart attack data, no stroke data, no diabetes-prevention data for retatrutide. Not one event-driven result.

This confuses people because of the trial names, so to be clear:

• TRIUMPH-3 enrolled 1,949 people with established cardiovascular disease — and measured weight, not events. It is not an outcomes trial.
• The actual cardiovascular and kidney outcomes trial is TRIUMPH-Outcomes (NCT06383390): around 10,000 participants, estimated completion 28 February 2029.

Compare that with the competition. SELECT showed semaglutide cut major cardiovascular events by about 20%. SURPASS-CVOT did the cardiovascular work for tirzepatide. Lilly plans to file retatrutide for approval in Q1 2027 — with no outcome trial read out. Approval, if it comes, will rest on weight, HbA1c, apnoea scores and knee pain.

The chain of reasoning is plausible: lose weight → better blood pressure, lipids, inflammation, glucose → fewer heart attacks. TRIUMPH-1 showed the middle links, directionally, without publishing the magnitudes. It did not show the last one.

And the lean-mass gap feeds straight into this. If a meaningful share of a 25% loss is muscle, then "25% weight loss" and "25% better health" are not the same sentence — especially in older patients. Nobody has measured that at these magnitudes, and nobody will have outcome data for another two and a half years.

Side effects

The gastrointestinal picture

Characterised in the paper as mild to moderate. A quarter of people on the top dose vomiting is still a quarter of people vomiting.

Stopping because of it

4 mg: 4.1% · 9 mg: 6.9% · 12 mg: 11.3% · placebo: 4.9%

Clean dose-dependence. About one in nine people on the top dose quit because of side effects. Across the programme it runs worse: up to 11.6% in TRIUMPH-2 and 13.5% in TRIUMPH-3.

Two signals that came from outside the company

Neither of these was in Lilly's press release. Both surfaced from independent scrutiny of the published paper.

• Dysesthesia — abnormal skin sensation — in more than 12% of people at the highest dose. Flagged by the UK Science Media Centre's expert panel.
• Dose-dependent symptoms of low blood pressure.

What we still don't have: transaminases and liver data from the trial, gallbladder disease, pancreatitis, hypoglycaemia rates, bone, serious adverse event rates and deaths. All presumably in the paper; none in the public releases.

The rest of the programme

All of the following is press release and conference only — none of it is peer-reviewed.

TRIUMPH-2 (NCT05929079) — obesity with type 2 diabetes, n=1,152, 80 weeks. Weight: 4 mg −12.7%, 9 mg −19.1%, 12 mg −20.8%, placebo −4.0%. HbA1c: −1.4% / −1.6% / −1.5% versus −0.2%; up to 40.0% got below 5.7%. Discontinuation for adverse events: 3.8% / 11.6% / 7.7% / 4.9% — note the 9 mg arm is worse than 12 mg, which is odd and unexplained. No confidence intervals, no p-values.

Worth explaining to readers: the effect is noticeably smaller in diabetes (−20.8% versus −25.0%). That is true of every incretin drug and it is expected, not a failure.

TRIUMPH-3 (NCT05882045) — obesity with established cardiovascular disease, n=1,949, randomised 1:1:2. Weight: 9 mg −21.6%, 12 mg −22.6%, placebo −3.2%. Discontinuation: 9.8% / 13.5% / 4.8%. Again — a weight trial, not an outcomes trial.

TRIUMPH-4 — a standalone knee osteoarthritis trial. No readout found.

How it compares — with a large caveat

There is no head-to-head trial. We searched for one and found nothing planned or running. Every "head-to-head comparison" in the search results was a telehealth or peptide-vendor page doing cross-trial arithmetic. The TRIUMPH obesity trials are all placebo-controlled with no active comparator.

Four reasons to hold this table loosely:

1. Different trials, different populations, different years, different placebo responses. TRIUMPH-1's placebo arm lost more than SURMOUNT-1's on the treatment-regimen estimand.
2. Different durations — 80 versus 72 versus 68 weeks. Retatrutide had 8–12 more weeks to accumulate, and none of these curves had fully flattened.
3. Estimand mismatch. Check which estimand the −20.9% and −14.9% represent before setting them beside −25.0%.
4. Lilly owns two of the three and has a commercial interest in the succession story.

A defensible summary: retatrutide appears to deliver several percentage points more than tirzepatide and perhaps ten more than semaglutide — at a higher side-effect and discontinuation burden, and without anyone having tested them against each other.

For Australians: not available, and the fakes are hurting people

The regulatory position

Retatrutide is not on the ARTG and is not approved by the TGA. It is not approved by any regulator anywhere in the world. Lilly's stated plan is a US filing in Q1 2027.

Reasoning from how tirzepatide and semaglutide went, Australian registration is 2028 at the earliest, and PBS listing for obesity later than that, if ever — GLP-1 medicines are not PBS-subsidised for weight management in Australia. Semaglutide is subsidised only for eligible patients with type 2 diabetes. Wegovy and Mounjaro for weight loss are full private cost.

So a third, newer, patent-fresh injectable would plausibly cost more than the current options. Which is precisely what drives the grey market.

The grey market is already causing harm here

This is the part of the article that might actually matter to someone reading it.

Six cases of acute liver injury in Victoria. The Victorian Department of Health issued a health alert on 19 June 2026 covering six cases since January in people using unapproved products labelled "Retatrutide", "Reta", "R-10" or "R-20". Presentations included malaise, jaundice, abdominal pain, dark urine and abnormal bruising, with transaminitis, raised bilirubin and coagulopathy. The alert's own conclusion: "additional contaminants may be contributing to the observed liver toxicity."

A ruptured oesophagus — and proof of what's in the vials. The TGA issued a safety advisory in September 2026, reported by ABC News on 13–14 September. A patient suffered uncontrollable vomiting and tore his oesophagus, requiring hospitalisation, after injecting a product sold as retatrutide.

Laboratory analysis found the vial contained no retatrutide at all. It contained semaglutide, at roughly eight times the dose in approved products.

TGA Chief Medical Advisor Robyn Langham: "The biggest risks with unapproved peptide products are not knowing what is in the vial, how much of, or even what substance it contains."

Dr Darcy Holt, gastroenterologist: "Without prompt medical attention a ruptured oesophagus is almost universally fatal."

The TGA's broader April 2026 advisory names retatrutide alongside BPC-157, TB-500, CJC-1295 and GHK-Cu, notes these are sold through social media and gyms, and warns that advertising them likely breaches Australian therapeutic goods law. Reported harms include anaphylaxis requiring hospitalisation, severe inflammation, full-body itching, palpitations, insomnia and blurred vision.

Retatrutide is also a prohibited substance in sport — Sport Integrity Australia lists it.

If you have taken something sold as retatrutide and feel unwell — yellowing of the skin or eyes, dark urine, persistent vomiting, severe abdominal pain — see a doctor and say what you took. The Poisons Information Centre is 13 11 26, 24 hours.

One more thing, and it's about how you found this page

Searching "retatrutide Australia" or "retatrutide dosing" returns results dominated almost entirely by sites selling it. Several are built to look like clinical references, with trial trackers and dosing protocols, and they outrank the TGA. We excluded every one of them from this article, and we'd suggest you treat any retatrutide "guide" that doesn't link to a journal, a regulator or a company filing as marketing.

What the clinicians are saying

The independent panel

The UK Science Media Centre convened experts on the topline announcement — and notably headlined its own briefing as a response to an announcement, not a published study.

• Prof Graham Finlayson, University of Leeds (declared: industry-collaborative obesity research, research funding and consultancy from nutrition and obesity organisations): "These are company-released topline findings rather than a full peer-reviewed scientific paper." Missing, he said: full statistical analysis, participant flow, handling of missing data, adverse event severity, and the trajectory of weight loss over time.
• Dr Marie Spreckley, University of Cambridge (declared: no personal financial interest in Lilly or retatrutide): "Without access to the complete dataset, it is not yet possible to fully assess issues such as adherence, missing data, subgroup effects, durability of response after discontinuation, and longer-term safety."
• Dr Simon Cork, Anglia Ruskin University (no conflicts declared): "So far these are only headline results, with the full peer reviewed paper still awaited."

That panel also surfaced the 12% dysesthesia rate the company hadn't mentioned.

And here is the arc worth sitting with: the publication on 29 September closed exactly the gaps those three asked about — and closing them revealed that the real-world weight loss figure was 25.0%, not 28.3%. The scepticism was warranted, and it was specific.

The investigator

Ania Jastreboff, lead author: "It was impressive to see that every dose of retatrutide resulted in clinically meaningful weight reduction for nearly all participants." True — and she is the Lilly-funded lead investigator, not independent commentary.

Dr Spencer Nadolsky

He has been in this from two directions, and the combination is a sensible position to borrow.

On the data: the Docs Who Lift episode of 8 June 2026, "Retatrutide Phase 3 Results: What the Data Actually Means," with his brother Dr Karl Nadolsky and a guest who was an actual TRIUMPH-1 participant. The participant described GI side effects that faded by month seven and heartburn managed with a low-dose PPI. They quote the 26% and 28% figures — the pre-publication efficacy numbers, which were all anyone had in June. The episode also covers "why the gray market research peptide version currently circulating is something both doctors strongly advise against."

On access: Nadolsky and Dr Mike Albert went public in August 2026 about going weeks without a substantive response from Lilly when seeking compassionate access for patients. Lilly opened a pre-approval access programme on 3 August 2026 for adults with refractory obesity and multiple serious complications — US-focused; Australian availability unknown.

So: pushing hard to get the real drug to patients who need it, while telling people plainly not to buy the fake. That is the right shape.

(We have the podcast's published topic list, not a transcript. We haven't attributed any specific opinion to him beyond what that description states.)

Other named reaction, on access rather than efficacy: Dr Angela Fitch said clinicians "are owed an explanation of some sort"; Dr Fatima Cody Stanford was sceptical that Lilly intended to extend access beyond the original patient.

What to take from this

It works, and more than anything before it. A quarter of body weight on the treatment-regimen estimand, nearly two thirds of people on the top dose losing 25% or more, large improvements in severe sleep apnoea and knee pain. Don't let the caveats obscure that.

Use 25.0%, not 28.3%, and definitely not 30.3%.

You cannot get it, legally, anywhere in the world. Not approved, not submitted in Australia, 2028 at the earliest, and unlikely to be PBS-subsidised when it arrives.

Do not buy it online. Six liver injuries in Victoria. A ruptured oesophagus. A vial that contained eight times the standard dose of a different drug entirely. This is the clearest consumer-safety message on this page.

If you want a GLP-1 now, there are two approved ones, both with cardiovascular outcome data retatrutide doesn't have yet. Talk to a GP about semaglutide or tirzepatide rather than waiting for this.

And if you're older, ask about muscle. The lean-mass question is unanswered at these magnitudes, resistance training and adequate protein are the evidence-based response, and they are free.

Frequently asked

How much weight did people lose on retatrutide? At 80 weeks on the 12 mg dose, 25.0% of body weight on the treatment-regimen estimand published in NEJM — the figure that includes everyone randomised. The widely quoted 28.3% is the efficacy estimand, describing people who stayed on treatment. A 532-person extension subgroup, selected for BMI ≥35, completing the trial and tolerating the top dose, reached 30.3% at 104 weeks.

Is retatrutide better than Mounjaro or Ozempic? On cross-trial comparison it appears stronger — 25.0% versus 20.9% for tirzepatide in SURMOUNT-1 and 14.9% for semaglutide in STEP-1. But no head-to-head trial exists or is planned, the trials differed in length, population and estimand, and retatrutide had a higher discontinuation rate. The two older drugs also have cardiovascular outcome data that retatrutide does not.

Can I get retatrutide in Australia? No. It is not on the ARTG, not approved by the TGA, and not approved by any regulator in the world. Lilly plans to file in the US in early 2027, which makes Australian registration 2028 at the earliest. Anything sold as retatrutide in Australia today is unapproved and unregulated.

Is retatrutide sold online safe? No, and there is Australian evidence of serious harm. Victoria recorded six cases of acute liver injury from products labelled "Retatrutide", "Reta", "R-10" or "R-20". A man required hospitalisation with a ruptured oesophagus after injecting a product sold as retatrutide — laboratory analysis found no retatrutide in the vial at all, just semaglutide at about eight times the approved dose. Poisons Information Centre: 13 11 26.

Does retatrutide cause muscle loss? Nobody knows at Phase 3 doses, because TRIUMPH-1 published no body-composition data. A Phase 2 substudy in people with type 2 diabetes found 62–69% of weight lost was fat, meaning roughly a third was lean mass, with lean mass falling up to 12.5%. That proportion is comparable to other incretin drugs and to dieting — but applied to a much larger total loss, so the absolute amount of lean tissue lost is larger.

Does it raise your heart rate? Glucagon receptor agonism is known to, and retatrutide is part glucagon agonist. But no heart-rate figures have been published in any of Lilly's three 2026 press releases, and we could not find the per-arm mean change in any legitimate source. The data is presumably in the published paper's appendix.

Does retatrutide prevent heart attacks? Unknown. No outcome data exists. TRIUMPH-3 enrolled people with cardiovascular disease but measured weight, not events. The cardiovascular and kidney outcomes trial, TRIUMPH-Outcomes, has around 10,000 participants and an estimated completion date of February 2029. Retatrutide will likely be filed for approval before any of it reports.

What are the side effects? On the 12 mg dose at 80 weeks: nausea 42.4%, diarrhoea 32.0%, constipation 26.1%, vomiting 25.3%, against placebo rates of 14.8%, 13.5%, 10.9% and 4.8%. About one in nine people on that dose stopped because of side effects. Independent review of the paper also found dysesthesia — abnormal skin sensation — in more than 12% at the top dose, and dose-dependent symptoms of low blood pressure.

Last reviewed 3 October 2026. TRIUMPH-1 was published in the New England Journal of Medicine on 29 September 2026; we have not been able to read the full paper, so confidence intervals are not quoted here and figures are drawn from Lilly's releases and from reporting of the publication. Industry funding and author affiliations are noted wherever disclosed. Figures from TRIUMPH-2, TRIUMPH-3 and the 104-week extension are press-release and conference data only and have not been peer-reviewed. We did not cite any peptide-vendor or grey-market source. This page is general information, not medical advice.