Retatrutide and type 2 diabetes: what the new Phase 3 results show

Retatrutide has already attracted attention for the amount of weight loss seen in obesity trials. New Phase 3 results now answer a different question: how well can the experimental drug address obesity and high blood sugar at the same time in people with type 2 diabetes?

In the TRIUMPH-2 trial, adults with type 2 diabetes and overweight or obesity who received the highest studied dose of retatrutide lost an average of 20.8% of their body weight over 80 weeks under the trial’s efficacy estimand. Blood sugar control improved substantially as well. The findings add a large late-stage dataset in a population that has historically lost less weight with incretin-based therapies than people without diabetes.

What TRIUMPH-2 tested

TRIUMPH-2 was a randomized, double-blind, placebo-controlled Phase 3 trial of once-weekly retatrutide in adults with type 2 diabetes who also had overweight or obesity. The study enrolled 1,152 participants and compared three maintenance doses of retatrutide, 4 mg, 9 mg and 12 mg, with placebo for 80 weeks.

Participants started at an average body weight of 106.4 kilograms, or about 235 pounds, with an average BMI of 38.2. Their average A1C was 7.7%. Randomization accounted for factors including baseline diabetes medication, baseline A1C and sex.

The primary weight endpoint was percent change in body weight at week 80. The trial also assessed A1C and several other metabolic measures.

How much weight did people lose?

Using the efficacy estimand reported by Eli Lilly, average weight loss at 80 weeks was 12.7% with 4 mg, 19.1% with 9 mg and 20.8% with 12 mg. The placebo group lost 4.0%.

For the 12-mg group, 20.8% translated to an average loss of 49.6 pounds. Among participants who began the trial with a BMI of at least 35, average weight loss at that dose reached 23.4%, or 60.8 pounds.

Another way to look at the result is by weight-loss thresholds. At 12 mg, 67.0% of participants lost at least 15% of their starting weight and 52.0% lost at least 20%. Lilly also reported that 59.5% of people in the 12-mg group no longer met the BMI threshold for obesity at the end of the study.

The term efficacy estimand matters. It estimates the treatment effect if participants adhered to the assigned treatment as intended. Results calculated using a treatment-regimen or intention-to-treat-style approach can be lower because they account differently for treatment discontinuation and missing data. Percentages from different estimands therefore should not be compared as though they are measurements of exactly the same thing.

The diabetes results may be just as important

Weight loss is only part of the story in TRIUMPH-2. Retatrutide also produced substantial reductions in A1C, a measure that reflects average blood glucose over roughly the previous two to three months.

From an average baseline A1C of 7.7%, the 4-mg group fell by 1.4 percentage points, the 9-mg group by 1.6 points and the 12-mg group by 1.5 points. Placebo reduced A1C by 0.2 points.

At week 80, 79.2% of participants receiving 9 mg and 79.0% receiving 12 mg had an A1C of 6.5% or lower. A1C below 5.7%, a threshold normally considered outside the prediabetes and diabetes ranges, was reached by 40.0% of the 9-mg group and 39.3% of the 12-mg group, compared with 4.4% with placebo.

Those numbers do not mean that retatrutide has been shown to permanently reverse or cure type 2 diabetes. A1C measured while someone is receiving a glucose-lowering medication describes glycemic control during treatment. It does not establish drug-free diabetes remission.

Why retatrutide is different from current GLP-1 drugs

Retatrutide is often grouped with GLP-1 medications, but its pharmacology is different. It is designed to activate three hormone receptors: glucose-dependent insulinotropic polypeptide, or GIP; glucagon-like peptide-1, or GLP-1; and glucagon.

Semaglutide targets the GLP-1 receptor. Tirzepatide targets both GIP and GLP-1 receptors. Retatrutide adds glucagon-receptor activity to those two pathways.

GLP-1 and GIP signaling can influence insulin secretion, appetite and food intake. The glucagon component is particularly interesting because glucagon has complex metabolic effects, including actions on the liver and energy expenditure. The goal is not simply to stack three appetite-suppressing signals. Retatrutide was engineered to balance activity across the three receptors in a way that may produce a larger overall metabolic effect.

For a broader explanation of this drug class and where retatrutide fits, see our guide to GLP-1 drugs and next-generation incretin therapies.

Why the diabetes population matters

One reason TRIUMPH-2 is informative is that people with type 2 diabetes often lose less weight in obesity-drug trials than participants without diabetes. The exact reasons are likely multifactorial and can include differences in metabolic physiology, background medications and the duration or severity of diabetes.

The contrast within retatrutide’s Phase 3 program illustrates the pattern. In TRIUMPH-1, which studied obesity or overweight without type 2 diabetes, the 12-mg dose produced 28.3% average weight loss under the reported efficacy estimate at 80 weeks. In TRIUMPH-2, the corresponding efficacy estimate in people with type 2 diabetes was 20.8%.

That does not make TRIUMPH-2 a head-to-head comparison between people with and without diabetes. The trials enrolled different populations and should not be treated as if participants had been randomized according to diabetes status. But it provides useful context for why a roughly 21% average reduction in this population has drawn attention.

What about side effects?

Retatrutide’s most common adverse events have generally been gastrointestinal, consistent with other incretin-based therapies. Nausea, diarrhea, vomiting and constipation have been prominent across the development program, particularly during dose escalation.

Safety interpretation requires more than counting common gastrointestinal symptoms. Larger and longer trials are needed to characterize less common adverse events and to understand the balance between benefit and risk across different patient groups.

This is also why impressive changes in weight, A1C, blood pressure or lipids should not automatically be translated into claims about preventing heart attacks, strokes or kidney failure. Those are clinical outcomes that require appropriately designed outcome trials.

How does this compare with earlier retatrutide evidence?

The new results build on rather than replace earlier studies. A Phase 2 trial in people with type 2 diabetes had already shown substantial A1C and weight reductions. A later body-composition substudy found that retatrutide reduced total fat mass and that the proportion of lean mass lost relative to total weight loss was similar to that seen with other obesity treatments.

In 2026, the Phase 3 TRANSCEND-T2D-1 trial also reported strong glucose lowering in adults with type 2 diabetes. Together, those studies establish that retatrutide’s effects are not limited to people enrolled primarily for obesity.

TRIUMPH-2 adds longer-duration Phase 3 evidence specifically in people who have both type 2 diabetes and overweight or obesity.

Retatrutide is still experimental

Despite the attention around the trial results, retatrutide is not an FDA-approved medication. Lilly describes it as investigational, and the company has said it plans regulatory submissions after completing its Phase 3 development package.

That distinction is particularly important because products marketed online as “retatrutide” are not approved versions of the drug used in Lilly’s clinical trials. Their identity, purity and dose cannot be assumed to match the investigational medicine.

What the new results actually tell us

TRIUMPH-2 strengthens the evidence that targeting GIP, GLP-1 and glucagon receptors simultaneously can produce large changes in both body weight and glycemic control. In people living with type 2 diabetes and overweight or obesity, the magnitude of weight loss at the higher doses was substantial, while A1C reductions brought many participants into ranges normally considered below the diagnostic threshold for diabetes.

But the study does not establish that retatrutide cures diabetes, nor does it yet tell us how its long-term clinical outcomes compare directly with semaglutide or tirzepatide. Those questions require different evidence, including head-to-head and cardiovascular-outcomes trials.

For now, the most defensible conclusion is narrower: retatrutide has produced substantial Phase 3 weight-loss and glucose-lowering effects in a population in which achieving both goals can be difficult. Whether that translates into a favorable long-term benefit-risk profile will depend on the full clinical and regulatory evidence.

References

1. Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. September 29, 2026. Lilly results release.
2. Eli Lilly and Company. A Study of Retatrutide (LY3437943) in Participants With Type 2 Diabetes Mellitus Who Have Obesity or Overweight (TRIUMPH-2), NCT05929079. Trial record.
3. Giblin K, Kaplan LM, Somers VK, et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes Obes Metab. 2026;28:83-93. DOI: 10.1111/dom.70209.
4. Coskun T, Wu Q, Schloot NC, et al. Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2 randomised trial. Lancet Diabetes Endocrinol. 2025;13:674-684. DOI: 10.1016/S2213-8587(25)00092-0.
5. Bajaj HS, Welch M, Shah P, et al. Efficacy and safety of retatrutide in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. Lancet. 2026;407:2402-2413. DOI: 10.1016/S0140-6736(26)00967-0.