Retatrutide for Type 2 Diabetes: -2.0% HbA1c, 16.8% Weight Loss (Phase 3 Confirmed)

Introduction

Type 2 diabetes affects roughly 37 million Americans, and for most, the path to managing it isn't simple. Glucose control and weight loss are usually treated as separate problems requiring separate medications — and even when blood sugar improves, weight often doesn't, or worse, climbs with certain treatments like insulin and sulfonylureas.

In March 2026, Eli Lilly announced topline results from TRANSCEND-T2D-1 — the first Phase 3 trial testing retatrutide specifically in people with type 2 diabetes. The results, since published in The Lancet and presented at the American Diabetes Association Scientific Sessions in June 2026, confirmed what the Phase 2 data had suggested: retatrutide can deliver substantial glucose control and substantial weight loss simultaneously, in a single weekly injection.

This is the trial that matters most for anyone managing type 2 diabetes who's been following retatrutide's development. Here's exactly what it showed.

TRANSCEND-T2D-1 at a Glance

Trial Design: Who Was Studied

TRANSCEND-T2D-1 (NCT06354660) enrolled 537 adults across 48 sites in the US, Mexico, and India between April 2024 and April 2025. This was specifically a monotherapy study — 85% of participants had not taken any antihyperglycemic medication for at least 90 days before enrollment, meaning the trial tested retatrutide's effect largely on its own, not as an add-on to existing diabetes drugs.

Eligibility required HbA1c between 7.0% and 9.5% and a BMI of at least 23 kg/m². That BMI threshold is notably lower than the obesity trials (TRIUMPH-1, TRIUMPH-4), reflecting that not everyone with type 2 diabetes has significant obesity — though in practice, the mean baseline BMI in this trial was 35.8, indicating most participants did have obesity alongside their diabetes.

Participants were randomized 1:1:1:1 to retatrutide 4mg, 9mg, 12mg, or placebo, all starting at a 2mg initiation dose with escalation every 4 weeks to the assigned target. The primary endpoint was change in HbA1c from baseline at week 40; weight change was the key secondary endpoint.

The Glucose Control Results

Across all three retatrutide doses, HbA1c reduction was statistically superior to placebo:

Note: ranges for the percentage of patients reaching glycemic targets were reported across the three retatrutide dose groups collectively rather than broken out individually in published summaries.

A meaningful number of patients went further than standard glycemic targets. Among 9mg and 12mg patients, 37–40% reached an HbA1c below 5.7% — the threshold generally considered within the normal, non-diabetic range — compared with 14% on placebo. This level of glycemic normalization, in patients who started with a mean HbA1c of 7.9%, is a substantial result for a single medication used largely as monotherapy.

For comparison, the Phase 2 trial that preceded TRANSCEND-T2D-1 (Rosenstock et al, published in The Lancet, 2023) tested retatrutide head-to-head against dulaglutide 1.5mg in 281 patients with type 2 diabetes already on metformin or diet/exercise alone, over 36 weeks. That earlier trial showed HbA1c reductions of up to 2.16% at the highest doses tested — directionally consistent with what TRANSCEND-T2D-1 later confirmed in a larger, placebo-controlled Phase 3 setting.

Weight Loss in the Diabetes Population

This is where the comparison to retatrutide's obesity trials needs to be precise, because the numbers are genuinely different — and that difference matters.

The 16.8% figure from TRANSCEND-T2D-1 is real, peer-reviewed, and confirmed — but it's not directly comparable to the 28%+ figures seen in TRIUMPH-1 and TRIUMPH-4, for two reasons. First, TRANSCEND-T2D-1 ran for 40 weeks compared to 68–80 weeks in the obesity trials, and weight loss was still increasing with no plateau when the trial ended — meaning the ceiling for this population at longer durations is unknown but likely higher than 16.8%. Second, people with type 2 diabetes tend to lose somewhat less weight than non-diabetics on the same GLP-1-class medications, a pattern observed across the entire drug class (semaglutide and tirzepatide show the same gap between their diabetes and non-diabetes trial populations).

If you've seen retatrutide's 28.7% figure cited in the context of diabetes treatment, that number comes from TRIUMPH-4 — which excluded participants with diabetes. The accurate, diabetes-specific figure from the only completed Phase 3 trial in this population is 16.8% at 40 weeks.

Cardiometabolic Benefits Beyond Glucose and Weight

TRANSCEND-T2D-1 measured several cardiovascular risk markers alongside its primary endpoints, with meaningful improvements reported:

• Triglycerides: reduced by up to 39.6%
• Non-HDL cholesterol: reduced by approximately 19.8%
• Systolic blood pressure: reduced by 6.4 mmHg
• Waist circumference: reduced by 4.9 inches

These improvements matter because cardiovascular disease is the leading cause of death in people with type 2 diabetes. A medication that simultaneously improves glycemic control, drives weight loss, and improves lipid and blood pressure markers addresses multiple risk factors that typically require separate medications to manage individually.

Side Effects: A Notably Different Profile Than the Obesity Trials

One of the more clinically interesting findings from TRANSCEND-T2D-1 is how much better tolerated retatrutide was in this population compared to TRIUMPH-4.

The dysesthesia rate in particular stands out — 4.4% in TRANSCEND-T2D-1 compared to 20.9% in TRIUMPH-4. The exact reason for this difference hasn't been established in published data, but it could relate to population differences (T2D patients vs the osteoarthritis-enriched TRIUMPH-4 cohort), the shorter trial duration (40 weeks vs 68 weeks, giving less time for the effect to develop), or simply trial-to-trial variation in a side effect that isn't fully understood mechanistically. Whatever the explanation, the lower discontinuation rate (5.1% vs 18.2%) suggests retatrutide may be meaningfully more tolerable in a diabetes-treatment context than in the obesity-treatment context most of this site's other content covers.

For a comprehensive breakdown of retatrutide's side effect profile across all trials, see our side effects guide.

How Retatrutide's Triple Mechanism Helps With Diabetes Specifically

Retatrutide activates three receptors — GLP-1, GIP, and glucagon — and each contributes to glucose control through a different pathway.

GLP-1 stimulates glucose-dependent insulin secretion (meaning it boosts insulin only when blood sugar is elevated, reducing hypoglycemia risk compared to drugs that stimulate insulin regardless of glucose level), slows gastric emptying, and suppresses appetite.

GIP amplifies the insulin-secreting effect of GLP-1 and has been shown in mechanistic studies to improve insulin sensitivity in adipose tissue specifically.

Glucagon, somewhat counterintuitively for a hormone that raises blood glucose, contributes to the overall metabolic improvement by increasing energy expenditure and accelerating fat loss — and the resulting weight loss itself improves insulin sensitivity throughout the body, creating a secondary glucose-lowering effect that compounds the direct hormonal action.

This is the mechanistic basis for why retatrutide's effect size in TRANSCEND-T2D-1 (up to -2.0% HbA1c) compares favorably to other GLP-1-class medications used for diabetes, despite testing in a largely treatment-naive population.

How Retatrutide Compares to Existing Diabetes Medications

Note: tirzepatide figures cited from a comparable 40-week T2D monotherapy trial design for the closest apples-to-apples comparison; cross-trial comparisons should be interpreted cautiously given differences in patient populations and trial conduct.

The pattern here is consistent with what's seen in the non-diabetes obesity trials: retatrutide's glucose control is roughly comparable to the best dual GLP-1/GIP agonist available (tirzepatide), but its weight loss is substantially higher — in this case, roughly 50% greater at a similar 40-week timepoint. The glucagon component appears to add weight loss without compromising glycemic efficacy.

For a head-to-head look at all three drug classes, see our vs Tirzepatide vs Semaglutide comparison.

A Note on Diabetes Prevention (Prediabetes)

Retatrutide has not yet been tested in a dedicated prediabetes prevention trial with published results as of June 2026. TRANSCEND-T2D-1 enrolled patients who already had type 2 diabetes (HbA1c 7.0–9.5%), not prediabetes.

It's biologically plausible that a drug producing this level of glucose improvement and weight loss could help prevent progression from prediabetes to type 2 diabetes — this is a well-established principle from lifestyle intervention research (the Diabetes Prevention Program showed a 58% risk reduction from intensive lifestyle changes alone) and has been demonstrated with other GLP-1-class drugs in prediabetic populations. But without a retatrutide-specific prediabetes trial, any claims about prevention timelines or specific outcomes in that population would be speculation rather than evidence. We'll update this section if and when dedicated prediabetes trial data becomes available.

Who This Data Is Most Relevant To

Based on TRANSCEND-T2D-1's design and population, the results are most directly applicable to:

• Adults with type 2 diabetes and HbA1c between 7.0% and 9.5%
• Patients not currently on other diabetes medications, or considering simplifying their regimen
• Patients with BMI ≥23, particularly those with obesity alongside diabetes (the trial's actual mean BMI was 35.8)
• Patients seeking a single medication that addresses both glycemic control and weight simultaneously

What the trial doesn't directly tell us: how retatrutide performs as an add-on therapy in patients already on multiple diabetes medications, how it performs beyond 40 weeks in this population, or how it compares directly to tirzepatide in a head-to-head trial (no such trial has been conducted).

What Comes Next

Lilly's TRANSCEND-T2D program includes three global registrational trials, having enrolled more than 2,050 participants since beginning in 2024. Additional results from this program are expected over the next year, which should clarify longer-term efficacy, performance as an add-on to existing therapies, and outcomes in broader diabetes populations.

For the latest on retatrutide's overall development timeline, see our complete retatrutide guide.

Conclusion

TRANSCEND-T2D-1 confirmed what Phase 2 data had suggested: retatrutide can deliver substantial, statistically superior glucose control compared to placebo — up to 2.0% HbA1c reduction — while simultaneously producing weight loss meaningfully beyond what's typical for diabetes-specific drug trials, at 16.8% with no plateau at 40 weeks.

The trial also revealed a notably better-tolerated side effect profile in this population than seen in TRIUMPH-4's obesity-trial population, particularly for dysesthesia and overall discontinuation — though the reasons for this difference aren't yet fully understood.

For the roughly 37 million Americans living with type 2 diabetes, a medication that addresses glycemic control and weight simultaneously — rather than requiring separate drugs for each — represents a meaningful potential shift in how the condition is managed, pending FDA review and approval.

Sources

• Bajaj HS, et al. "Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial." The Lancet, 2026.
• Eli Lilly and Company. TRANSCEND-T2D-1 Phase 3 topline results announcement. March 19, 2026.
• Rosenstock J, Frias J, Jastreboff AM, et al. "Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active comparator-controlled phase 2 trial." The Lancet, 2023;402:529-544.
• Jastreboff AM, et al. "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." New England Journal of Medicine, 2023.
• Eli Lilly TRIUMPH-4 Phase 3 topline results (December 2025).
• Eli Lilly TRIUMPH-1 Phase 3 topline results (May 21, 2026).