When TRIUMPH-1 read out, almost every headline fixed on one figure: 28.3% average body weight loss at the 12mg dose over 80 weeks. Fair enough — it's the largest average weight loss reported for any retatrutide trial to date. But buried inside that same trial was a second, much smaller study of 243 people with moderate-to-severe obstructive sleep apnoea, and its retatrutide results are arguably the most clinically concrete thing to come out of the programme so far. Sleep apnoea is measured with a hard number, not a symptom questionnaire — and that number moved a long way.

The retatrutide results hiding inside TRIUMPH-1

TRIUMPH-1 wasn't one trial. It was a master trial of 2,339 adults with obesity or overweight, randomised 1:1:1:1 to retatrutide 4mg, 9mg, 12mg or placebo over 80 weeks, with two smaller "basket" trials nested inside it — one for people who also had knee osteoarthritis pain, and one for people who also had moderate-to-severe obstructive sleep apnoea.

In the 243-participant sleep apnoea basket, Lilly reported that retatrutide 12mg reduced the apnoea-hypopnoea index (AHI) by 36.1 events per hour at 80 weeks — a 60.6% reduction from a baseline of 58.6 events per hour. AHI counts how many times per hour of sleep a person's breathing stops or becomes dangerously shallow. A baseline of 58.6 is severe disease; roughly one interruption a minute, all night.

Two caveats before anyone gets carried away. First, these figures come from Lilly's own announcement and conference presentation, not from a full peer-reviewed publication of the sleep apnoea basket, so the placebo-adjusted treatment effect and the complete secondary endpoints aren't yet available for independent scrutiny. Second, 243 participants is a modest sample by phase 3 standards — it's a registrational sub-study, not a standalone mega-trial. You can read more about how the wider programme is structured on our clinical trials page.

Why this matters more than another weight number

The obesity drug field has a credibility problem that has nothing to do with efficacy: kilos lost are an intermediate measure. What patients and payers actually want to know is whether the disease burden shifts. Sleep apnoea is one of the cleanest tests of that, because AHI is measured objectively by polysomnography and the condition is strongly and mechanically linked to excess weight — fat deposition around the upper airway and abdomen directly worsens airway collapse during sleep.

So a 60.6% cut in AHI is a different class of evidence to a percentage on the scales. It is a measured change in an organ-level disease process. For context on how retatrutide's three-receptor mechanism differs from single- and dual-agonists, see what is retatrutide.

How it stacks up against tirzepatide — carefully

The obvious comparison is SURMOUNT-OSA, the phase 3 programme that put tirzepatide (Mounjaro/Zepbound) on the map for sleep apnoea. Published in the New England Journal of Medicine, it enrolled participants with mean baseline AHI of 51.5 events per hour (trial 1, not using PAP therapy) and 49.5 (trial 2, using PAP). At week 52, mean AHI change was −25.3 events per hour with tirzepatide versus −5.3 with placebo in trial 1, and −29.3 versus −5.5 in trial 2.

Put the raw numbers side by side and retatrutide's −36.1 looks larger. But this is a cross-trial comparison, not a head-to-head, and the differences are not trivial: TRIUMPH-1 ran to 80 weeks versus 52 for SURMOUNT-OSA, the retatrutide basket started from a more severe baseline (58.6 events per hour), and the populations and PAP-use rules were defined differently. Percentage reductions from different baselines are not interchangeable either. No trial has yet randomised people to retatrutide versus tirzepatide for sleep apnoea, so the honest answer is that the two drugs have not been compared.

The Australian precedent that already exists

This is one case where the Australian angle is real rather than manufactured. Mounjaro (tirzepatide) is already registered by the TGA for the treatment of moderate-to-severe obstructive sleep apnoea in adults with obesity — Australia's first registered pharmacological treatment for OSA, granted on the strength of SURMOUNT-OSA.

That matters because it means the regulatory template is not hypothetical here. An obesity medicine has already earned an OSA indication from the TGA off the back of AHI data. Retatrutide remains investigational and is not TGA-approved for anything; Lilly has said it plans to begin regulatory filings from 2027, starting in the United States. But in a country where roughly 66.8% of adults are overweight or obese, a second drug with sleep apnoea evidence attached is worth tracking. More on the local picture at retatrutide in Australia, and on the tolerability profile at safety.

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FAQ

Does retatrutide help sleep apnoea?

In the 243-participant obstructive sleep apnoea basket trial nested inside phase 3 TRIUMPH-1, retatrutide 12mg reduced the apnoea-hypopnoea index by 36.1 events per hour (60.6%) at 80 weeks, from a baseline of 58.6. These figures come from Lilly's announcement and conference presentation, not yet a full peer-reviewed publication.

What were the main retatrutide results from TRIUMPH-1?

TRIUMPH-1 randomised 2,339 adults to retatrutide 4mg, 9mg, 12mg or placebo for 80 weeks. The 12mg dose produced average body weight loss of about 28.3%, with 45.3% of participants losing 30% or more of their body weight.

Is retatrutide better than Mounjaro for sleep apnoea?

Nobody knows. Retatrutide's AHI reduction in TRIUMPH-1 was numerically larger than tirzepatide's in SURMOUNT-OSA, but the trials differed in length (80 weeks versus 52), baseline severity and population. There has been no head-to-head trial of the two drugs in sleep apnoea.

Is retatrutide approved in Australia for sleep apnoea?

No. Retatrutide is investigational and not TGA-approved for any indication. Tirzepatide (Mounjaro) is currently the only medicine registered by the TGA for moderate-to-severe obstructive sleep apnoea in adults with obesity.

Sources

This article is for general information only and is not medical advice. Retatrutide is an investigational medicine and is not approved by the TGA. Talk to a qualified Australian health professional about your own treatment. retatrutide.net.au is an independent information site and is not affiliated with, endorsed by or sponsored by Eli Lilly and Company.