The headline number from retatrutide's pivotal phase 3 trial — up to 28.3% average body weight loss at 80 weeks — has been repeated so often it has almost stopped meaning anything. But as the detailed TRIUMPH-1 data has rolled out over the past few weeks, a different set of figures has started doing more work: how many people finished the trial no longer meeting the BMI definition of obesity at all. On the 12mg dose, roughly two in three did. That reframes what retatrutide weight loss results actually represent — not just a bigger percentage, but a change in diagnostic category.

Retatrutide weight loss results: the numbers behind the average

Reporting on the detailed TRIUMPH-1 readout describes 65.3% of participants on retatrutide 12mg reaching a BMI under 30 — below the clinical threshold for obesity — and 33.3% reaching a BMI under 25, which is inside the "healthy weight" band. In a prespecified analysis of participants who started with a BMI of 35 or above, average loss was reported at about 85 lb (roughly 38.5kg), or 30.3%, with coverage attributing that figure to a longer 104-week horizon rather than the headline 80-week endpoint.

Two caveats matter. First, these are trial-population results, presented and reported ahead of the kind of full peer-reviewed publication that lets independent researchers pick apart every analysis. Second, "no longer obese by BMI" is a category change, not a cure — BMI says nothing about body composition, and it says nothing about what happens after treatment stops. We've written separately about the clinical trial evidence base and how these endpoints are constructed.

Why category exit matters more than a percentage

Percentages are hard to act on. Categories are what health systems are actually built around. BMI cut-offs decide who is eligible for subsidised medicines, who gets referred for bariatric surgery, who is knocked back for certain elective procedures, and in some settings what insurance costs.

That is where the Australian implication sits. The AIHW puts around two-thirds of Australian adults in the overweight or obese range, and the thresholds that define those groups are the same ones used to gate access to treatment here. A drug that moves a large share of users across the BMI 30 line doesn't just change a statistic — it changes which category of care they're being managed under. See our Australia page for where retatrutide currently sits locally: investigational, not TGA-approved, with Eli Lilly signalling a US filing from 2027.

The rest of the picture: comorbidities and comparators

TRIUMPH-1 ran "basket" cohorts alongside the main trial, and the reported reductions there are substantial: knee osteoarthritis pain scores (WOMAC subscale) down by as much as 73.1% from baseline, and apnoea-hypopnoea index down by up to 60.6% from a baseline of 58.6 events per hour in participants with obstructive sleep apnoea. Those are single-trial figures, and sleep apnoea and osteoarthritis endpoints are notoriously sensitive to trial design, so treat them as promising rather than settled.

On comparators, a large review published in Annals of Internal Medicine — 26 randomised trials, 15,491 adults without diabetes, 12 GLP-1 receptor agonists and co-agonists — had already placed retatrutide at the front of the field with an estimated 24.2% weight loss at 12mg, ahead of tirzepatide (17.8%) and subcutaneous semaglutide (13.9%) at their maximum evaluated doses. The phase 3 results sit above that earlier estimate over longer treatment. For the mechanism behind the gap — glucagon receptor agonism added to GLP-1 and GIP — see what is retatrutide.

Where the tolerability line is drawn

The trade-off hasn't disappeared. The reported adverse event profile in TRIUMPH-1 was dose-related nausea, diarrhoea, constipation and vomiting, with dysesthesia (altered skin sensation) and urinary tract infections also reported and generally described as mild to moderate. Dysesthesia is one of the few signals that looks distinctive to retatrutide rather than shared with existing incretin drugs, and it's worth watching as fuller data is published. Our safety page tracks what has been reported so far.

Meanwhile, the wider programme keeps filling in: TRIUMPH-2 (obesity or overweight with type 2 diabetes) reported up to 20.8% average loss at 80 weeks, and TRIUMPH-3 (severe obesity with established cardiovascular disease) up to 22.6%, with Lilly stating it plans to submit a Biologics License Application to the FDA in Q1 2027. Cardiovascular event numbers in those trials were small and not statistically conclusive, which the company's own release makes clear.

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FAQ

What are the latest retatrutide weight loss results?

The pivotal TRIUMPH-1 trial reported average body weight loss of up to 28.3% at 80 weeks on the 12mg dose, with detailed data indicating 65.3% of that group fell below a BMI of 30 and 33.3% below a BMI of 25. A prespecified analysis of participants starting at BMI 35 or above reported about 30.3% loss over a longer 104-week horizon.

Is retatrutide better than tirzepatide or semaglutide?

On weight loss alone, the trial numbers so far favour retatrutide — a 26-trial review estimated 24.2% at 12mg versus 17.8% for tirzepatide and 13.9% for subcutaneous semaglutide at their maximum evaluated doses. There is still no large head-to-head trial and no long-term cardiovascular outcomes data for retatrutide, so "better" remains an incomplete answer.

When will retatrutide be approved?

Eli Lilly has said it plans to file a Biologics License Application with the US FDA in the first quarter of 2027. Australian availability would require a separate TGA submission and evaluation after that, so retatrutide remains investigational and unapproved in Australia.

What are the main retatrutide side effects reported so far?

The most commonly reported effects in TRIUMPH-1 were dose-related nausea, diarrhoea, constipation and vomiting. Dysesthesia (altered skin sensation) and urinary tract infections were also reported and were generally characterised as mild to moderate.

Sources

Disclaimer: retatrutide.net.au is an independent information site and is not affiliated with, endorsed by or sponsored by Eli Lilly and Company. This article is general information only and is not medical advice. Retatrutide is investigational and is not approved by the TGA for use in Australia. Trial figures cited come from company announcements and conference/media reporting, some of which is not yet fully peer-reviewed. Always speak with your GP or a qualified health professional about your own treatment.