The retatrutide phase 3 story has quietly changed shape. For a year the headline number was TRIUMPH-1: roughly 28.3% average body weight loss at 12mg over 80 weeks in adults with obesity, with 45.3% of participants losing 30% or more. Then came TRIUMPH-2, in adults who have both type 2 diabetes and obesity or overweight — and the number dropped to 20.8% at the same 12mg dose. That gap of roughly seven percentage points is the most interesting thing in the retatrutide data package right now, and it is not a failure. It is a well-known pattern across the entire incretin class, and understanding it tells you more about how these drugs work than any single headline percentage.

What TRIUMPH-2 and TRIUMPH-3 actually showed

Eli Lilly reported topline results from two further phase 3 trials in July 2026, taking the programme to five positive phase 3 studies.

TRIUMPH-2 enrolled adults with type 2 diabetes and obesity or overweight. At 80 weeks, average weight loss was reported as about 12.7% on 4mg, 19.1% on 9mg and 20.8% on 12mg.

TRIUMPH-3 studied adults with severe obesity and established cardiovascular disease, with weight reduction of up to 22.6% at 80 weeks. Alongside the weight change, the 12mg arm showed reductions of 37.0% in triglycerides, 16.5% in non-HDL cholesterol, 9.3 mmHg in systolic blood pressure and 19.0 cm (7.5 inches) in waist circumference.

Two caveats matter and should be said plainly. First, these are topline company results and conference presentations — the full peer-reviewed publications for TRIUMPH-2 and TRIUMPH-3 are the documents that will let independent researchers pick the data apart. Second, TRIUMPH-3 enrolled people with existing heart disease but it is not a cardiovascular outcomes trial: it was not designed to prove that retatrutide prevents heart attacks or strokes, and commentary at the time noted the cardiovascular risk-reduction signal was less clear-cut than the weight and metabolic numbers. Semaglutide has dedicated outcomes data; retatrutide does not yet.

Why people with type 2 diabetes lose less weight

This is not unique to retatrutide. Semaglutide and tirzepatide both produce noticeably less weight loss in trials of people with type 2 diabetes than in trials of people without it. The leading explanations, all still partly hypothesis:

1. Insulin is a storage hormone

Many people with type 2 diabetes are on insulin or insulin-secreting medicines such as sulfonylureas. Those drugs push glucose into cells and favour fat storage, working against the energy deficit the incretin is creating. Trials also have to protect against hypoglycaemia, which limits how aggressively background therapy can be stripped back.

2. Losing glucose in the urine stops

Before treatment, poorly controlled diabetes can mean hundreds of calories a day literally leaving the body in urine as glucose. Improve glycaemic control and that calorie leak closes — a real metabolic gain, but one that shows up on the scales as slower weight loss.

3. Different starting biology

People with longstanding type 2 diabetes often have reduced beta-cell function, more visceral and liver fat, and a lower resting metabolic rate for a given body weight. The mechanism of a triple agonist — GLP-1 plus GIP plus glucagon — is designed to add an energy-expenditure lever on top of appetite suppression, which is precisely why the diabetes result is worth watching. Even blunted, 20.8% is a very large number for this population.

The number that may matter more than weight

For a person living with type 2 diabetes, weight is a means, not the endpoint. Glycaemic control is. Data presented at ADA 2026 from TRANSCEND-T2D-1 showed an HbA1c reduction of around 2 percentage points — broadly comparable to the best results reported for semaglutide and tirzepatide in similar populations, though cross-trial comparisons are indirect and should be treated cautiously.

Put together with the TRIUMPH-3 lipid and blood pressure movements, the emerging picture is of a drug that shifts the whole cardiometabolic panel, not just the scales. Whether that translates into fewer cardiovascular events is a separate question that only an outcomes trial can answer. You can follow how the full trial programme is structured and what each study is designed to prove.

What this means for regulators — and for Australia

Lilly has said the clinical package now supports global submissions for obesity, knee osteoarthritis pain and obstructive sleep apnoea, with a US biologics licence application planned from the first quarter of 2027. Notice what is not on that list: a standalone type 2 diabetes indication is running on its own track, through the TRANSCEND programme.

That sequencing has a genuine Australian consequence. Around 1.3 million Australians live with diagnosed diabetes, the overwhelming majority type 2, and in Australia the reimbursement pathway for a diabetes indication looks very different to the pathway for an obesity indication — semaglutide and tirzepatide are PBS-listed for type 2 diabetes but not for weight management alone. Which indication the TGA receives first, and in what order, will shape who can realistically afford retatrutide here long before price lists appear. Our Australia page tracks the regulatory position as it moves.

Retatrutide remains investigational and is not TGA-approved for any use.

The honest read on the gap

Do not read 20.8% as a disappointment. Read it as calibration. If you have type 2 diabetes, the phase 3 evidence suggests you should expect meaningful but smaller weight loss than the 28.3% headline, alongside HbA1c improvements that may matter more for your long-term health. If you do not have diabetes, the TRIUMPH-1 numbers are the relevant ones. Tolerability follows the same dose-dependent pattern in both groups — gastrointestinal effects dominate, and you can read more on the safety picture.

Want the phase 3 publications, regulatory filings and Australian availability news as they land? Join the free updates list.

FAQ

How much weight do people with type 2 diabetes lose on retatrutide?

In the phase 3 TRIUMPH-2 trial, adults with type 2 diabetes and obesity or overweight lost an average of about 12.7% at 4mg, 19.1% at 9mg and 20.8% at 12mg over 80 weeks — less than the roughly 28.3% reported at 12mg in TRIUMPH-1, which enrolled people with obesity but not diabetes.

Why is retatrutide weight loss lower in people with diabetes?

It is a pattern seen with semaglutide and tirzepatide too. The likely contributors include insulin and insulin-stimulating medicines promoting fat storage, the loss of calories excreted as urinary glucose once blood sugar improves, and differences in baseline metabolic biology. None of these are fully proven mechanisms.

How many phase 3 trials has retatrutide passed?

Lilly has reported five positive phase 3 studies in the TRIUMPH programme as of mid-2026, covering obesity, obesity with type 2 diabetes, obesity with established cardiovascular disease, knee osteoarthritis pain and obstructive sleep apnoea. Several results are topline or conference presentations rather than full peer-reviewed publications.

Does retatrutide reduce heart attacks and strokes?

Not proven. TRIUMPH-3 enrolled people with established cardiovascular disease and showed improvements in weight, triglycerides, non-HDL cholesterol and blood pressure, but it was not designed as a cardiovascular outcomes trial. A dedicated outcomes study would be required to demonstrate event reduction.

Sources

Disclaimer: This article is general information only and is not medical advice. Retatrutide is an investigational medicine and is not approved by the TGA or the FDA. Trial results described here include topline company announcements and conference presentations that have not all been peer reviewed. Always speak with 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.