Retatrutide Clinical Trial Results: What the TRIUMPH Data Shows

In the Phase 2 NEJM trial, people taking the highest dose of retatrutide lost an average of 24.2% of their body weight in 48 weeks — and every single person on the 8mg or 12mg dose lost at least 5% of their body weight. Every single one.

That number matters because semaglutide (Wegovy) tops out at −15.5% on the 2.4 mg dose and −18.8% on the 7.2 mg high dose at 72 weeks, per its FDA label. Tirzepatide (Zepbound) reached −20.9% on 15 mg in SURMOUNT-1, per its label. These are separate trials in separate populations, not a head-to-head, but retatrutide is landing above both.

Key Takeaways

• Retatrutide is a triple agonist — it activates GLP-1, GIP, and glucagon receptors simultaneously, the leading explanation for why its trial results run above those of single and dual agonists
• The Phase 2 trial published in the NEJM (2023) showed dose-dependent weight loss from -8.7% to -24.2% across dose groups
• The TRIUMPH Phase 3 program now runs to ten registered trials on ClinicalTrials.gov — TRIUMPH-1 through TRIUMPH-9 plus the TRIUMPH-Outcomes cardiovascular and kidney trial — covering obesity, type 2 diabetes, sleep apnea, osteoarthritis, chronic low back pain and cardiovascular disease. Lilly describes four of them as the initial registrational core
• TRIUMPH-4 (obesity plus knee osteoarthritis) was the program's first successful Phase 3 trial; Lilly described the result as weight loss of up to an average of 71.2 lbs alongside osteoarthritis pain relief
• TRANSCEND-T2D-1 showed A1C reductions of up to 2.0% and average weight loss of 36.6 lbs (16.8%) on 12 mg at 40 weeks in adults with type 2 diabetes, published in The Lancet alongside the ADA presentation
• In May–June 2026, the pivotal TRIUMPH-1 obesity trial reported 28.3% average weight loss (70.3 lbs) on 12 mg at 80 weeks; TRIUMPH-2 and TRIUMPH-3 followed in July 2026
• Retatrutide is still investigational. Lilly says the clinical data package is complete and it plans to submit a Biologics License Application to the FDA in Q1 2027, which puts an approval decision in late 2027 at the earliest

These numbers are real, and they're extraordinary. But there's still meaningful uncertainty. Phase 3 trials are ongoing, long-term safety data is still accumulating, and "average" doesn't mean "you." Here's what the actual data says, trial by trial.

What Is Retatrutide? A Quick Primer

Retatrutide (LY3437943) is an injectable drug developed by Eli Lilly. You take it once a week — same delivery format as Ozempic or Zepbound. What makes it different is that it hits three metabolic pathways instead of one or two.

Most GLP-1 drugs work by slowing gastric emptying and telling your brain you're full. Tirzepatide added GIP, which amplifies the insulin response and may affect fat cells directly. Retatrutide adds glucagon receptor activation on top of that, which is thought to raise energy expenditure and push the body to mobilize stored fat more aggressively.

The triple mechanism is the leading explanation for why the weight loss numbers are higher, though the trials measured weight, not mechanism — no published retatrutide trial has isolated how much of the effect comes from the glucagon arm.

If you want a deeper breakdown of how this drug works at the receptor level, see our guide: What Is Retatrutide?

The Phase 2 NEJM Trial: Where It All Started

The Phase 2 trial (NCT04881760) was published in the New England Journal of Medicine in June 2023. It's the foundational dataset. 338 adults with obesity (BMI ≥30, or ≥27 with a comorbidity) and no type 2 diabetes were randomized to placebo or to one of six retatrutide arms, which the paper pools into four dose groups — 1 mg, 4 mg, 8 mg and 12 mg. The 4 mg and 8 mg groups each ran two different starting-dose schemes. The trial ran 48 weeks, and its primary endpoint was weight change at 24 weeks; the 48-week figures everyone quotes were secondary endpoints.

This was a double-blind, placebo-controlled study. The gold standard design. And the results were not subtle.

A few things stand out. At 12mg, 83% of participants lost at least 15% of their body weight. The trial pre-specified ≥5%, ≥10% and ≥15% weight reduction as secondary endpoints precisely because those are the thresholds obesity trials use to mark clinically meaningful response. Getting 83% of a trial arm past the highest of them is a striking result.

Beyond weight, the paper reports improvements in cardiometabolic measures including blood pressure, glucose and lipids over the 48 weeks. The drug wasn't just moving the scale — it was improving the underlying metabolic picture.

How Phase 2 Numbers Compare to Approved Drugs

Honestly, comparing these drugs can feel like reading stats for athletes in different eras. The trials aren't perfectly matched — different populations, different durations, different designs. But the broad comparison is still useful context for understanding what retatrutide might offer relative to what's already out there.

One caveat that matters more than it looks: the semaglutide and tirzepatide figures above are intention-to-treat results, while every retatrutide Phase 3 number Lilly has released is the efficacy estimand — what would have happened had participants stayed on drug. TRIUMPH-1's treatment-regimen estimand, the closer analogue, was −25.0% at 12 mg. Each step up in mechanism complexity has still added several percentage points of weight loss, and adding glucagon activation appears to do the same, but these are separate trials in separate populations, not a ranked list.

How Does Retatrutide Compare to Bariatric Surgery?

In May 2026, the pivotal Phase 3 TRIUMPH-1 trial reported that participants on 12mg lost an average of 70.3 lbs (28.3%) over 80 weeks, with 45.3% achieving at least 30% weight loss — a level Lilly's own release describes as "long associated with bariatric surgery." In a study extension, participants with a baseline BMI of 35 or higher continued losing weight and reached an average of 85.0 lbs (30.3%) at 104 weeks, which coverage of the readout framed as the first drug to approach surgery-level weight loss. This is a cross-trial comparison, not a head-to-head surgical study, and bariatric surgery has its own distinct durability and risk tradeoffs.

The TRIUMPH Phase 3 Program: Overview

Eli Lilly didn't just run one or two Phase 3 trials. They built an entire program called TRIUMPH. Lilly has never published an expansion of the acronym, so treat it as a program name and nothing more. What is documented is the shape of it: ten TRIUMPH-numbered Phase 3 trials are now registered, and Lilly describes the initial registrational core — obesity, obstructive sleep apnea and knee osteoarthritis pain — as four global trials that began in 2023 and enrolled more than 5,800 participants. Several of those run as master protocols with nested basket trials, letting one study support more than one indication.

This breadth is deliberate. Lilly is positioning retatrutide for multiple indications — not just obesity, but the whole cluster of diseases that obesity drives.

TRIUMPH-1 Topline Results: The Pivotal Obesity Readout

If you only read one trial in this program, read this one. TRIUMPH-1 (NCT05929066) is the pivotal obesity trial the FDA submission is built on. Lilly announced topline results in May 2026 and presented the full dataset on June 6, 2026 at the American Diabetes Association's 86th Scientific Sessions.

The design, in plain terms: a Phase 3, 80-week, randomized, double-blind, placebo-controlled master trial in adults with obesity or overweight, with two nested basket trials running inside it — one for knee osteoarthritis pain, one for moderate-to-severe obstructive sleep apnea. 2,339 participants were randomized 1:1:1:1 to retatrutide 4 mg, 9 mg, 12 mg or placebo, from a mean baseline weight of 248.5 lbs. Everyone on drug started at 2 mg and stepped up every four weeks to their assigned target dose. Every weight figure below is the efficacy estimand — the effect estimated had participants stayed on treatment. On the treatment-regimen estimand, which counts everyone regardless of adherence, the same arms came in at −17.6%, −23.7% and −25.0%.

The number that reframes what these drugs do isn't the percentage — it's the BMI crossover. 65.3% of participants on 12 mg finished below a BMI of 30, meaning they no longer met the BMI criterion for obesity. 33.3% finished below a BMI of 25, in the range classified as healthy weight. Trial populations are not the general population, and an average is not a promise. But those are category changes, not just scale movement.

The 104-Week Extension

TRIUMPH-1 had a pre-specified extension built in. 532 participants who started with a BMI of 35 or higher, completed the 80-week study, and tolerated their assigned dose continued for another 24 weeks, with a blinded escalation to their maximum tolerated dose of 9 mg or 12 mg. Those continuing on 12 mg averaged 85.0 lbs (30.3%) lost at 104 weeks — weight loss that was still going at two years, in the group that started heaviest.

What the Two Basket Trials Found

The nested baskets are why Lilly can pursue three indications from one trial:

• Knee osteoarthritis pain: WOMAC pain subscale scores fell by up to 4.3 points (73.1%) from a baseline of 6.0.
• Obstructive sleep apnea: the apnea-hypopnea index fell by up to 36.1 events per hour (60.6%) from a baseline of 58.6 events per hour — a severe-OSA population at entry.

Cardiometabolic markers moved in the same direction at 80 weeks: triglycerides down 41.0%, non-HDL cholesterol down 24.2%, systolic blood pressure down 12.3 mmHg, and waist circumference down 9.5 inches (24.1 cm) at the top of the range reported.

TRIUMPH-1 Adverse Events

Read the last row before the first ones. GI side effects are near-universal talking points with this class; the number that decides whether a drug is livable is how many people quit over them. At 12 mg, 11.3% did — a bit over one in nine, against 4.9% on placebo. At 4 mg, discontinuation was indistinguishable from placebo, and that arm still averaged 47.2 lbs.

TRIUMPH-2 and TRIUMPH-3: The Harder Populations

On July 23, 2026, Lilly reported the two trials that test retatrutide where weight loss is usually hardest to get: people with type 2 diabetes, and people with severe obesity plus established cardiovascular disease. Both met their primary endpoints, and both ran 80 weeks.

Two things worth flagging honestly about TRIUMPH-3. First, the cardiovascular event data is not a win yet: MACE occurred less often than the trial was designed to expect in both arms. For time to first MACE-5 event (all-cause death, heart attack, stroke, heart failure event or coronary revascularization), there were 44 events on retatrutide versus 52 on placebo — a hazard ratio of 0.82 with a 95% confidence interval of 0.55 to 1.22, which crosses 1.0 and therefore does not establish benefit. For the narrower MACE-3 endpoint the hazard ratio was 1.12 (0.64 to 1.96). Second, the risk-factor movement was real: at the highest dose, triglycerides fell 37.0%, non-HDL cholesterol 16.5%, systolic blood pressure 9.3 mmHg, waist circumference 7.5 inches, and hs-CRP 51.2%. The dedicated cardiovascular outcomes trial, TRIUMPH-Outcomes, doesn't finish until 2029.

Discontinuation due to adverse events ran higher in these sicker populations: 11.6% (9 mg) and 7.7% (12 mg) in TRIUMPH-2, and 9.8% (9 mg) and 13.5% (12 mg) in TRIUMPH-3, against 4.9% and 4.8% on placebo respectively.

TRIUMPH-4: The 28.7% Result

In December 2025, Eli Lilly released Phase 3 results from TRIUMPH-4. This was the first major Phase 3 efficacy readout, and it exceeded the Phase 2 numbers.

Worth being precise about what this trial was, because it is frequently described as a plain obesity study. TRIUMPH-4 (NCT05931367) randomized 445 participants with obesity or overweight who also had osteoarthritis of the knee and without diabetes, 1:1:1 to retatrutide 9 mg, 12 mg or placebo. It was a 68-week trial with co-primary endpoints: WOMAC pain subscale score and percent change in body weight. 84.0% of participants entered with a BMI of 35 or higher. In its Q4 2025 results, Lilly described it as retatrutide's "first successful Phase 3 trial," delivering weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain.

At 68 weeks, participants on the 12 mg dose lost an average of 28.7% of their body weight on the efficacy estimand — that is the 71.2 lbs, from a mean baseline of 248.5 lbs. On the treatment-regimen estimand the same arm came in at −23.7% (60.0 lbs). Either way it is a larger mean reduction than any Phase 3 obesity trial had reported before it, including tirzepatide's −20.9% in SURMOUNT-1 — though those are separate trials in different populations, not a head-to-head.

A few notes on what this does and doesn't mean for you:

• 28.7% is the mean. Some people lost more. Some lost less.
• The trial had a titration schedule lasting ~16 weeks before the 12 mg group hit its maintenance dose — steps at 2 mg, 4 mg, 6 mg and 9 mg, four weeks apart. Weight loss was gradual, not a cliff.
• The trial population was adults with obesity or overweight who also had knee osteoarthritis, 84% of them with a BMI of 35 or higher — a narrower and heavier group than the broad obesity population in TRIUMPH-1. Individual results will vary.
• Tolerability at those two doses was the trial's weak spot: discontinuation due to adverse events ran 12.2% (9 mg) and 18.2% (12 mg) against 4.0% on placebo, and Lilly notes some of those were for perceived excessive weight loss. Among participants with a baseline BMI ≥35 the rates fell to 8.8% and 12.1%.
• Long-term follow-up data doesn't exist yet. What happens at year 3 or 5 is still unknown.

Still. 28.7% is a big number, and the detailed results are due at a medical meeting and in a peer-reviewed journal.

TRANSCEND-T2D-1: March 2026 Phase 3 Results

In March 2026, Lilly announced positive topline Phase 3 results from TRANSCEND-T2D-1 — the first Phase 3 trial specifically in people with type 2 diabetes.

The drug hit its primary and all key secondary endpoints. Full results were presented on June 6, 2026 at the ADA Scientific Sessions and published simultaneously in The Lancet. The specifics: A1C fell by an average of up to 2.0% from a baseline of 7.9% at 40 weeks, with up to 90% of participants on retatrutide reaching an A1C below 7.0% and up to 46% below 5.7% — the threshold for normal blood sugar. The 12 mg group also lost an average of 36.6 lbs (16.8%), and weight loss had not plateaued when the trial ended at 40 weeks. That is exceptional for a diabetes population, where incretin drugs typically underperform their obesity-only trials.

TRANSCEND-T2D-1 (NCT06354660) randomized 537 adults with type 2 diabetes who were not on any diabetes medication, 1:1:1:1 to retatrutide 4 mg, 9 mg, 12 mg or placebo.

Why does this matter? Because type 2 diabetes and obesity are deeply intertwined. Most people with T2D are also managing their weight. A drug that moves both needles at once would be a meaningful clinical advance. One thing to be clear about, though: the submission Lilly has actually described covers obesity, obstructive sleep apnea and knee osteoarthritis pain — not type 2 diabetes. TRANSCEND-T2D is a separate three-trial program that Lilly says has enrolled more than 2,050 participants, with more readouts still to come.

Beyond Weight: What Else the Trials Are Measuring

This is where retatrutide gets interesting beyond the scale. The Phase 2 data and early Phase 3 signals suggest benefits that go well beyond just losing pounds.

Liver fat: A Nature Medicine phase 2a substudy (2024) followed the 98 participants in the Phase 2 obesity trial who had metabolic dysfunction-associated steatotic liver disease and at least 10% liver fat at baseline. Mean relative liver fat fell 82.4% at 24 weeks on 12 mg and 81.4% on 8 mg, versus +0.3% on placebo, and 86% of the 12 mg group reached a normal liver fat fraction under 5%. That is a dramatic number, from a small substudy rather than a dedicated liver trial. Treatment options here are no longer absent — semaglutide picked up an accelerated approval for noncirrhotic MASH with F2–F3 fibrosis in 2025, per its label — but they are still few.

Sleep apnea: this has now reported. The obstructive sleep apnea basket nested inside TRIUMPH-1 cut the apnea-hypopnea index by up to 36.1 events per hour (60.6%) from a baseline of 58.6. Lilly says obstructive sleep apnea is one of the three indications its completed data package supports. The drug already approved for this is tirzepatide — Zepbound carries an FDA indication for moderate-to-severe OSA in adults with obesity. Semaglutide does not; obstructive sleep apnea appears nowhere in the Wegovy label, which covers weight reduction, cardiovascular risk reduction and MASH. Retatrutide is lining up behind Zepbound, not Wegovy.

Cardiovascular outcomes: TRIUMPH-3 studied people with established cardiovascular disease and reported in July 2026. Weight loss was substantial (22.6% at 12 mg), but cardiovascular events were too few in both arms to demonstrate benefit — the MACE-5 hazard ratio was 0.82 with a confidence interval of 0.55 to 1.22. The definitive answer comes from TRIUMPH-Outcomes, a 10,000-participant event-driven trial that doesn't complete until 2029. That's the semaglutide SELECT playbook, and it hasn't played out yet.

Knee osteoarthritis: also reported, twice. TRIUMPH-4 was the standalone knee OA trial and the program's first Phase 3 win; the knee OA basket inside TRIUMPH-1 then cut WOMAC pain subscale scores by up to 4.3 points (73.1%) from a baseline of 6.0. Knee osteoarthritis pain is the third indication in Lilly's submission package.

The full picture of retatrutide isn't just "better Ozempic." Lilly lists seven areas it is studying the drug in: obesity and overweight with a weight-related condition, type 2 diabetes, knee osteoarthritis pain, moderate-to-severe obstructive sleep apnea, chronic low back pain, cardiovascular and renal outcomes, and metabolic dysfunction-associated steatotic liver disease. Three of those are in the first submission. The rest are still open questions.

What Were the Side Effects in Clinical Trials?

The most common side effects in both Phase 2 and Phase 3 trials were gastrointestinal — nausea, vomiting, diarrhea, and constipation. These are the same side effect profile seen with all incretin-based drugs. They're typically worst early in treatment and improve as your body adjusts.

In the Phase 2 trial, serious adverse events were uncommon and did not rise with dose: the posted results show 3 of 70 on placebo and between 0 and 2 per retatrutide arm. Dose escalation is deliberately slow to blunt the GI burden — in Phase 2 the 12 mg group stepped 2 → 4 → 8 → 12 mg at four-week intervals, reaching target at week 12; the Phase 3 trials added 6 mg and 9 mg steps, so the 12 mg group reaches target at week 16.

A few things worth flagging from the trial data:

• Dose-dependent heart rate increases were observed in Phase 2, peaking at 24 weeks and declining thereafter. Heart rate increase is a labeled monitoring point for this class generally
• Hepatobiliary and pancreatic events were rare in Phase 2 rather than common: one serious acute cholecystitis in an 8 mg arm and one serious acute pancreatitis in the 12 mg arm, out of 338 participants. Cholelithiasis did not reach the 5% reporting threshold in any arm
• Nothing emerged that was unheard of for the incretin class, but the sensory events grouped as dysesthesia are more prominent with retatrutide than with tirzepatide, and are discussed below

For a full breakdown of what the side effect data actually shows, see: Retatrutide Side Effects: What the Data Shows

Dysesthesia: A Drug-Specific Signal

Dysesthesia — an abnormal and sometimes unpleasant skin or sensory sensation, such as tingling, burning or altered touch — shows up more often with retatrutide than with tirzepatide. In the Phase 3 TRIUMPH-1 trial it was reported in 5.1%, 12.3%, and 12.5% of participants on the 4mg, 9mg, and 12mg doses respectively, compared with 0.9% on placebo, and events were generally mild to moderate with most resolving during treatment. TRIUMPH-4, which used only the two highest doses, reported 8.8% and 20.9% against 0.7% on placebo.

It is worth correcting a common framing here: this is not unique to retatrutide. Dysesthesia is a labeled adverse reaction for semaglutide, and it is dose-dependent — the Wegovy label reports it in 22% of patients on the 7.2 mg dose against 6% on 2.4 mg and 0.3% on placebo. What the retatrutide data suggests is a dose- and exposure-related sensory effect that runs across potent incretin therapy, not a signal peculiar to the triple agonist. The Phase 2 trial saw the same cluster at the top dose: the posted results list allodynia in 4 of 62 participants on 12 mg, plus hyperaesthesia and sensitive skin. These are trial adverse-event rates, not established adverse-reaction rates from an approved label — retatrutide does not have one yet.

Pancreatitis and Thyroid: Class-Level Cautions

Pancreatitis (inflammation of the pancreas) is a recognized class-level concern for incretin-based drugs, and it carries through to retatrutide as a low-but-not-zero monitored risk: Lilly's TRIUMPH-6 eligibility criteria exclude people with a prior history of pancreatitis. The GLP-1 drug class also carries a precautionary thyroid C-cell warning based on rodent studies, and Lilly's eligibility rules exclude anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2); this is a preclinical, class-based precaution rather than evidence that retatrutide itself causes thyroid cancer. If you have any of these conditions in your history, discuss them with your care team before considering any incretin therapy.

• Urinary tract infections were reported as a lower-frequency event in the Phase 3 TRIUMPH-1 trial, occurring in 7.5%, 8.8%, and 8.4% of participants on the 4mg, 9mg, and 12mg doses versus 5.3% on placebo, and were generally mild to moderate with most resolving during treatment

When Could Retatrutide Be Available?

Honestly, this is the question everyone wants answered. Here's the current timeline picture:

• Phase 3 readouts: done. TRIUMPH-1 reported in May–June 2026; TRIUMPH-2 and TRIUMPH-3 in July 2026
• FDA submission: Lilly says it plans to file a Biologics License Application in Q1 2027, stated in its July 23, 2026 trial announcement and repeated in its August 5, 2026 quarterly results
• FDA review period: under the PDUFA VII goals covering fiscal years 2023–2027, FDA aims to act on 90% of standard original BLA submissions within 10 months of the 60-day filing date, or within 6 months for a priority review
• Earliest realistic approval is therefore late 2027, with 2028 the base case on a standard review clock

These timelines can slip. They often do. What has changed is the nature of the risk: the remaining gating items are manufacturing documentation, the filing decision and the review itself, not whether the trials work. For the full breakdown, see when will retatrutide be available.

If you want to track real before-and-after experiences from early access contexts, see: Retatrutide Before and After

Retatrutide vs Tirzepatide: What the Trials Suggest

People ask this a lot. Lilly is actually running a direct head-to-head Phase 3 trial — TRIUMPH-5 (NCT06662383), retatrutide versus tirzepatide in adults with obesity, roughly 800 participants, primary completion listed for November 2026. It is closed to enrollment. Results aren't in yet.

What we can say from the existing trial data:

• Retatrutide's Phase 2 result at 12 mg was −24.2% over 48 weeks. Tirzepatide has no comparable Phase 2 obesity trial to set against it — its dose-finding Phase 2 work was in type 2 diabetes, where weight loss runs far lower, so any "Phase 2 versus Phase 2" figure you see for tirzepatide in obesity is not a real comparison
• Retatrutide's Phase 3 results (−28.7% in TRIUMPH-4, −28.3% in TRIUMPH-1, both efficacy estimand) run above tirzepatide's −20.9% at 15 mg in SURMOUNT-1
• These aren't controlled comparisons — different populations, durations, protocols and estimands

The head-to-head will be the definitive answer. But based on mechanism alone, the addition of glucagon activation provides a plausible biological reason for superior efficacy. Glucagon receptor activation pushes energy expenditure — the combination of eating less AND burning more efficiently may simply be additive in a way dual agonism isn't.

Frequently Asked Questions

What is the TRIUMPH trial for retatrutide?
TRIUMPH is Eli Lilly's Phase 3 clinical development program for retatrutide. Lilly has not published an expansion of the acronym, so any spelled-out version you see is someone's guess. Ten TRIUMPH trials are registered on ClinicalTrials.gov — TRIUMPH-1 through TRIUMPH-9 plus TRIUMPH-Outcomes — covering obesity, type 2 diabetes, sleep apnea, cardiovascular and kidney outcomes, knee osteoarthritis and chronic low back pain. Lilly calls four of them the initial registrational core. Retatrutide's type 2 diabetes trials run under a separate program name, TRANSCEND-T2D, and its liver work sits inside the SYNERGY-Outcomes master protocol.

How much weight loss did the retatrutide Phase 2 trial show?
The Phase 2 NEJM trial (2023) showed dose-dependent weight loss from -8.7% at the 1mg dose to -24.2% at the 12mg dose over 48 weeks. At the 12mg dose, 100% of participants lost at least 5% of body weight, and 83% lost at least 15%.

What did the retatrutide Phase 3 results show?
Five Phase 3 trials have now reported positive results. TRIUMPH-4 (knee osteoarthritis) was the first, in December 2025. TRIUMPH-1, the pivotal obesity trial, reported 28.3% average weight loss (70.3 lbs) on 12 mg at 80 weeks, rising to 30.3% (85.0 lbs) at 104 weeks in a pre-specified extension for participants who started with a BMI of 35 or higher. TRANSCEND-T2D-1 showed A1C reductions of up to 2.0% at 40 weeks. TRIUMPH-2 (type 2 diabetes) delivered 20.8% and TRIUMPH-3 (severe obesity with cardiovascular disease) 22.6%, both at 80 weeks.

What were the TRIUMPH-1 topline results?
Announced in May 2026 and presented in full on June 6, 2026: the 4 mg, 9 mg and 12 mg arms averaged 19.0% (47.2 lbs), 25.9% (64.4 lbs) and 28.3% (70.3 lbs) weight loss at 80 weeks. 65.3% of the 12 mg group finished below a BMI of 30 and 33.3% below a BMI of 25. In the nested basket trials, knee osteoarthritis pain fell by up to 4.3 WOMAC points (73.1%) and the apnea-hypopnea index by up to 36.1 events per hour (60.6%). Discontinuation due to adverse events was 11.3% on 12 mg versus 4.9% on placebo.

What does the retatrutide NEJM study say?
The NEJM June 2023 publication reported Phase 2 results: a least-squares mean weight reduction of 24.2% at 48 weeks in the 12 mg group, larger than semaglutide's 14.9% in STEP-1 or tirzepatide's 20.9% in SURMOUNT-1, though both of those trials ran longer and neither was a head-to-head. The trial was a randomized, double-blind, placebo-controlled study of 338 adults with obesity, with weight change at 24 weeks as its primary endpoint.

Is retatrutide better than tirzepatide?
Based on available trial data, retatrutide shows higher average weight loss in clinical trials than tirzepatide — 24.2–28.7% versus −20.9% at tirzepatide's 15 mg dose in SURMOUNT-1. However, these comparisons are not direct head-to-head studies, and the retatrutide figures are efficacy-estimand results while the SURMOUNT-1 figure is intention-to-treat. Eli Lilly is running an actual head-to-head trial — TRIUMPH-5, retatrutide versus tirzepatide, primary completion listed for November 2026 — and it hasn't reported yet. Mechanism-based reasoning suggests the addition of glucagon activation may produce additive benefits, but the definitive answer awaits the direct comparison data.

What are the side effects of retatrutide in clinical trials?
The most common side effects are gastrointestinal: nausea, vomiting, diarrhea, constipation. In TRIUMPH-1, nausea ran 28.6% to 42.4% across the three doses against 14.8% on placebo. These are similar to other GLP-1/GIP-based drugs and were managed through gradual dose escalation. The one side effect that draws separate attention is dysesthesia — altered skin sensation — reported in 12.5% of the 12 mg arm in TRIUMPH-1 and 20.9% of the 12 mg arm in TRIUMPH-4. It is not unique to retatrutide; semaglutide's label reports it in 22% of patients on the 7.2 mg dose.

When will retatrutide be available?
Not before late 2027, and 2028 is the more realistic answer. The pivotal trials have reported; the remaining step is Lilly's Biologics License Application, which the company says it plans to submit in Q1 2027. From there the FDA takes up to 60 days to accept the filing, then aims to act within 6 months (priority review) or 10 months (standard review) of that date.

Where the Research Stands Right Now

The clinical trial evidence for retatrutide is genuinely impressive — larger mean weight reductions than any obesity drug that came before it has reported. The Phase 2 data set the mark. The Phase 3 TRIUMPH-4 result went higher. The T2D Phase 3 data read out positive in March 2026. The mechanism has a plausible biological rationale for why triple agonism might work better.

But let's be real about the uncertainty. The pivotal obesity trials have now reported, and the extension data runs to 104 weeks — but that is still two years, not five. We don't know what happens when you stop; TRIUMPH-6, the weight-maintenance trial, doesn't complete until 2028. The cardiovascular outcomes trial, TRIUMPH-Outcomes, runs to 2029, and TRIUMPH-3 did not establish a cardiovascular benefit — its MACE confidence intervals crossed 1.0. The liver disease program is still enrolling. And the Phase 3 numbers on this page come from company announcements and conference presentations rather than peer-reviewed papers: TRANSCEND-T2D-1 is published in The Lancet, but the full papers for TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 and TRIUMPH-4 are still to come. The Phase 2 figures are the exception — those are in NEJM and in the posted ClinicalTrials.gov results.

What we have right now is an extremely promising picture with some critical gaps still being filled in. The data that exists is the best weight loss drug data ever generated in controlled trials. The data that doesn't exist yet matters too.

If you're watching this space for yourself or someone you care about, the milestone to watch now is the FDA submission itself, targeted for Q1 2027. TRIUMPH-1 — the pivotal obesity trial that drives it — has already delivered. In the meantime, what to check before buying retatrutide covers the questions worth asking about anything sold now.

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Disclaimer: This article is for educational and informational purposes only. Retatrutide is an investigational drug that has not received FDA approval. All clinical trial data discussed is from published scientific literature, Eli Lilly press releases, and ClinicalTrials.gov. Nothing in this article constitutes medical advice. Consult a licensed healthcare provider before making any medical decisions.