Retatrutide: Complete Evidence Review (2026)

Last updated: June 2026

Medical disclaimer: This article is for informational purposes only and is not medical advice. Retatrutide is an investigational drug and is not FDA-approved as of 2026. Do not start, stop, or change any treatment based on what you read here. Consult your doctor.

Retatrutide is Eli Lilly's investigational triple-hormone-receptor agonist for obesity and related conditions. It is the first drug in advanced trials to target three gut and metabolic hormone pathways at once. This review pulls the real numbers from the Phase 2 NEJM and Lancet papers and the unfolding Phase 3 TRIUMPH program, with every figure cited to a primary source.

What is retatrutide and how does its triple-agonist mechanism work?

Retatrutide is a once-weekly injectable peptide that activates three receptors: GIP, GLP-1, and glucagon. That triple action is why it is called a "GGG" or triple agonist. Its research code is LY3437943.

Semaglutide (Ozempic, Wegovy) hits one receptor: GLP-1. Tirzepatide (Mounjaro, Zepbound) hits two: GIP and GLP-1. Retatrutide adds a third, glucagon, to the mix (NEJM, 2023).

Here is what each receptor does. GLP-1 curbs appetite and slows how fast your stomach empties. GIP also helps control appetite and may improve how the body handles fat.

Glucagon is the surprising one. People know it as the hormone that raises blood sugar, but it also boosts energy expenditure, meaning your body burns more calories at rest. Adding glucagon is the bet that drove retatrutide's unusually large weight loss (Nature Medicine, 2024).

Why combine all three at once? Single-hormone drugs work, but each pathway has a ceiling. Stacking three lets a lower dose of any one hormone do part of the job, which spreads the effect across more biology.

The glucagon piece is what sets retatrutide apart from every approved drug. Glucagon nudges the liver and fat tissue to burn stored energy, so the body spends more calories even at rest (Nature Medicine, 2024).

There is a trade-off to manage. Because glucagon can raise blood sugar, the GLP-1 and GIP arms have to pull sugar back down. Trials suggest the balance works, with blood sugar improving rather than worsening (Lancet, 2023).

Retatrutide is given as a once-weekly shot under the skin. Doses are titrated up slowly over months, the same stepwise approach used for semaglutide and tirzepatide to limit nausea (NEJM, 2023).

You can see where retatrutide fits among the newer drugs in our next-gen GLP-1 pipeline landscape.

How much weight did retatrutide produce in trials?

On the top 12 mg dose, retatrutide cut body weight by 24.2% at 48 weeks in the Phase 2 obesity trial, and by 28.3% at 80 weeks in the Phase 3 TRIUMPH-1 trial. Those are among the largest reductions ever reported for a weight-loss drug.

The Phase 2 trial (Jastreboff et al.) enrolled 338 adults with obesity and no diabetes. It tested 1, 4, 8, and 12 mg doses against placebo (NEJM, 2023).

Here is the headline efficacy data, broken out by dose and trial phase.

Trial (population)	Dose	Mean weight loss	Placebo	Duration	Source
Phase 2 (obesity, no T2D)	1 mg	-8.7%	-2.1%	48 wk	NEJM 2023
Phase 2 (obesity, no T2D)	4 mg	-17.1%	-2.1%	48 wk	NEJM 2023
Phase 2 (obesity, no T2D)	8 mg	-22.8%	-2.1%	48 wk	NEJM 2023
Phase 2 (obesity, no T2D)	12 mg	-24.2%	-2.1%	48 wk	NEJM 2023
TRIUMPH-1 (obesity, no T2D)	4 mg	-19.0%	-2.2%	80 wk	Lilly 2026
TRIUMPH-1 (obesity, no T2D)	9 mg	-25.9%	-2.2%	80 wk	Lilly 2026
TRIUMPH-1 (obesity, no T2D)	12 mg	-28.3%	-2.2%	80 wk	Lilly 2026

The dose response is steep. Each step up in dose adds more weight loss, and the curve had not clearly flattened at 48 weeks in Phase 2 (NEJM, 2023).

Phase 2 weight loss was still trending down when the trial ended. That hinted the true ceiling was higher, which Phase 3 later confirmed at 80 weeks.

It also helps to look past the average. The share of people hitting big targets is striking, especially at 12 mg.

Weight-loss threshold (Phase 2, 48 wk)	8 mg	12 mg	Placebo
≥5% loss	100%	100%	27%
≥10% loss	91%	93%	9%
≥15% loss	75%	83%	2%

In TRIUMPH-1, the surgical-level results stand out. On the 12 mg dose, 62.5% of people lost at least 25% of their body weight, and 45.3% lost 30% or more, versus near zero on placebo (Lilly TRIUMPH-1, 2026).

Here is how the high-threshold response stacks up across the three TRIUMPH-1 doses.

Weight-loss threshold (TRIUMPH-1, 80 wk)	4 mg	9 mg	12 mg	Placebo
≥25% loss	27.8%	52.9%	62.5%	2.2%
≥30% loss	15.3%	37.9%	45.3%	0.5%
≥35% loss	5.9%	20.8%	27.2%	0.3%

Those ≥35% numbers are unusual. Losing more than a third of body weight on a drug starts to approach what bariatric surgery delivers, which is why analysts have called retatrutide a potential category leader (Scientific American, 2026).

One honest note on raw pounds. The 12 mg group lost an average of 70.3 lbs over 80 weeks, but the trial included an extension to 104 weeks, and the long curve matters for judging durability (Lilly TRIUMPH-1, 2026).

How does weight loss differ by subgroup?

Weight loss is consistently larger in people without diabetes than in people with type 2 diabetes, and the highest doses drive the biggest gap. That diabetes pattern shows up across GLP-1 drugs, and retatrutide is no exception.

The clearest subgroup split is diabetic versus non-diabetic. In the obesity Phase 2 trial (no diabetes), the 12 mg dose hit -24.2% at 48 weeks. In the separate type 2 diabetes Phase 2 trial, the same class of patient on 12 mg lost about 16.9% at 24 weeks (Lancet, 2023).

Here is the subgroup breakout pulled from the published trials.

Subgroup	Trial / dose	Weight loss	Source
No diabetes	Phase 2 obesity, 12 mg, 48 wk	-24.2%	NEJM 2023
Type 2 diabetes	Phase 2 T2D, 12 mg, 24 wk	-16.9% (17.2 kg)	Lancet 2023
No diabetes	TRIUMPH-1, 12 mg, 80 wk	-28.3% (70.3 lb)	Lilly 2026
Obesity + knee OA, no diabetes	TRIUMPH-4, 12 mg, 68 wk	-28.7% (71.2 lb)	Lilly 2025
Sex (51.8% male in Phase 2)	Phase 2, prespecified	Effect seen across both sexes	NEJM 2023

On baseline BMI and sex, the Phase 2 trial ran prespecified exploratory subgroup analyses and reported that the weight-loss effect held across baseline BMI categories and across sex, with no signal that one group failed to respond (NEJM, 2023).

One caveat on the diabetes number. The T2D figure is at 24 weeks, while the obesity figures run to 48 or 80 weeks. Shorter time partly explains the smaller loss, on top of the known diabetes effect.

The TRIUMPH-4 group is worth noting too. These were adults with obesity and knee osteoarthritis but no diabetes, and they lost up to 28.7% at 68 weeks (Healio, 2025).

Why does diabetes blunt weight loss? The leading idea is that diabetes changes how the body stores and burns energy, so the same drug pushes the scale less. It is a consistent class effect, not a flaw unique to retatrutide.

What about baseline weight? Heavier starting BMI tends to mean more total pounds lost, even when the percentage is similar. The Phase 2 subgroup analysis did not flag any BMI band that failed to respond (NEJM, 2023).

A fair limit on all of this. Most subgroup splits come from the smaller Phase 2 trials, so they are exploratory, not definitive. The larger TRIUMPH trials will give firmer subgroup answers as they report through 2026.

What did retatrutide do for blood sugar and other conditions?

Beyond weight, retatrutide sharply lowered A1C in type 2 diabetes, cleared most liver fat in a fatty-liver substudy, and reduced knee osteoarthritis pain in Phase 3. Its effects reach well past the scale.

Start with blood sugar. In the Phase 2 type 2 diabetes trial, the 12 mg dose cut A1C by roughly 2.0 to 2.2 percentage points at 24 weeks. Up to 82% of participants reached an A1C under 6.5%, and up to 31% dropped below 5.7%, the non-diabetic range (Lancet, 2023).

Next, the liver. A Phase 2a substudy in people with obesity and high liver fat measured fat with MRI-PDFF, the gold-standard scan (Nature Medicine, 2024).

The liver results were dramatic. At the highest dose, retatrutide cut liver fat by about 86% at 48 weeks, and roughly 93% of participants reached normal liver-fat levels. Zero placebo participants normalized (Nature Medicine, 2024).

Then there is the knee. The Phase 3 TRIUMPH-4 trial studied 445 adults with obesity and moderate-to-severe knee osteoarthritis. It tested 9 mg and 12 mg over 68 weeks (HCPLive, 2025).

Knee pain dropped meaningfully. Retatrutide cut WOMAC pain scores by up to 75.8%, and 14.1% of the 9 mg group were completely free of knee pain at 68 weeks, versus 4.2% on placebo (Healio, 2025).

Blood pressure improved too. Phase 2 showed reductions in systolic blood pressure across the higher doses, a knock-on benefit of large weight loss (NEJM, 2023).

So why does one drug touch sugar, liver, knees, and pressure all at once? Most of these gains track with weight loss itself, plus the direct metabolic effects of the three hormones. Losing 20% or more of body weight tends to move many health markers together.

You can compare these approved and investigational drugs on our medications directory.

Where is retatrutide in Phase 3 (TRIUMPH) and the FDA process?

Retatrutide is in the Phase 3 TRIUMPH program, which began reading out in late 2025, with an FDA filing expected in late 2026 to early 2027. It is not yet approved for any use.

TRIUMPH is a multi-trial program with more than 5,800 participants enrolled in the initial set. The trials use a master-protocol design (Lilly TRIUMPH-1, 2026).

Here is the program status as of mid-2026.

Trial	Population	Key readout	Status	NCT ID
TRIUMPH-1	Obesity/overweight, no diabetes (n=2,339)	28.3% loss at 12 mg, 80 wk	Reported May 2026	NCT05929066
TRIUMPH-2	Obesity + type 2 diabetes	A1C + weight	Expected Q2-Q3 2026	NCT05882045
TRIUMPH-3	Obesity + cardiovascular disease	Weight + CV outcomes	Expected Q3-Q4 2026	NCT05882048
TRIUMPH-4	Obesity + knee osteoarthritis (n=445)	28.7% loss; pain relief, 68 wk	Reported Dec 2025	NCT06014099

TRIUMPH-1 read out first, in May 2026, with the headline 28.3% weight loss at 12 mg over 80 weeks (Scientific American, 2026).

Lilly has said data from TRIUMPH-2 and TRIUMPH-3 will follow later in 2026. The company kept guidance for a regulatory submission in late 2026 to early 2027 (Lilly TRIUMPH-1, 2026).

What does that mean for timing? A standard FDA review of 10 to 12 months would put the earliest realistic approval in late 2027 or 2028. Until then, retatrutide stays investigational.

The master-protocol design is worth understanding. Instead of running fully separate trials, TRIUMPH shares structure and controls across studies, which speeds enrollment and keeps the data comparable (Lilly TRIUMPH-1, 2026).

One caution on compounded versions. Because retatrutide is not approved, any product sold today as "retatrutide" is not an FDA-reviewed medicine. There is no approved supply, dose, or label, which is a real safety gap to flag.

What are retatrutide's side effects?

The most common side effects are gastrointestinal: nausea, vomiting, diarrhea, and constipation, and they rise with the dose. That profile matches other GLP-1 drugs.

In Phase 2, GI events were mostly mild to moderate and were eased by starting at a low dose and stepping up slowly (NEJM, 2023).

Dose matters for dropouts. In TRIUMPH-1, discontinuation for side effects was 4.1% on 4 mg, 6.9% on 9 mg, and 11.3% on 12 mg, against 4.9% on placebo (Lilly TRIUMPH-1, 2026).

One thing to watch is heart rate. Phase 2 saw dose-dependent increases that peaked around 24 weeks, then eased (NEJM, 2023).

Most GI side effects show up during titration, when the dose is climbing. Once people reach a steady dose, nausea and related symptoms usually settle down. That is why clinicians step the dose up slowly rather than starting high.

No new or unexpected safety signal had emerged through Phase 3 as of mid-2026. The profile so far looks like a stronger version of the familiar GLP-1 side-effect pattern, scaled with dose (Lilly TRIUMPH-1, 2026).

For a full breakdown, see our retatrutide side effects by system and dose guide.

What does the evidence NOT yet support?

Retatrutide has no completed cardiovascular outcomes trial, no FDA approval, and no published long-term safety data beyond about two years. Big questions remain open.

First, hard cardiovascular outcomes. TRIUMPH-3 is testing weight loss in people with heart disease, but a dedicated outcomes trial proving fewer heart attacks or strokes has not reported (Lilly TRIUMPH-1, 2026).

Second, weight regain. As with all of these drugs, it is unclear how much weight comes back after stopping, and no long-term off-drug data exists for retatrutide.

Third, the glucagon question. Activating glucagon raises blood sugar in theory, and while trials managed this, the long-term metabolic picture in diverse patients is not settled (Lancet, 2023).

Fourth, special populations. There is no approved-label evidence for pregnancy, adolescents, or people with kidney or liver disease. Treat all current numbers as trial data, not a prescription.

Fifth, the MASH liver claim is promising but early. The fatty-liver result is from a small Phase 2a substudy, not a pivotal MASH trial with liver-biopsy endpoints (Nature Medicine, 2024).

Sixth, head-to-head proof. Retatrutide's averages look larger than tirzepatide's and semaglutide's, but those are cross-trial comparisons. No published trial has pitted retatrutide directly against another GLP-1 drug.

Seventh, durability after dose changes. The TRIUMPH-1 extension out to 104 weeks will help, but two years is still short for a drug people may take for life. Long-run cardiovascular and cancer-safety signals take years to mature.

The honest summary is this. Retatrutide has the most impressive short-term weight and metabolic data of any drug in late-stage trials. It also has the most unanswered long-term questions, precisely because it is so new (Scientific American, 2026).

Frequently Asked Questions

Is retatrutide FDA-approved in 2026?

No. As of mid-2026, retatrutide is investigational and not approved by the FDA for any use. Eli Lilly has guided toward a regulatory filing in late 2026 to early 2027, which means the earliest possible approval would be late 2027 or 2028.

How much weight do people lose on retatrutide?

In the Phase 2 obesity trial, the 12 mg dose produced 24.2% weight loss at 48 weeks. In the Phase 3 TRIUMPH-1 trial, the same dose reached 28.3% over 80 weeks, with 45.3% of people losing at least 30% of their body weight (Lilly, 2026).

How is retatrutide different from tirzepatide?

Tirzepatide targets two receptors, GIP and GLP-1. Retatrutide adds a third, glucagon, which boosts calorie burn. In trials, retatrutide's average weight loss has run higher than tirzepatide's, though no head-to-head trial has been published.

What did retatrutide do for type 2 diabetes?

In the Phase 2 diabetes trial, the 12 mg dose lowered A1C by about 2.0 to 2.2 points at 24 weeks, with up to 82% of participants reaching an A1C below 6.5%. Those patients also lost about 16.9% of their body weight (Lancet, 2023).

What are the most common retatrutide side effects?

Gastrointestinal symptoms are most common: nausea, vomiting, diarrhea, and constipation. These rise with the dose and are usually mild to moderate. In TRIUMPH-1, 11.3% of people on the 12 mg dose stopped treatment due to side effects (NEJM, 2023).

Related Reading

• Retatrutide dosage: what the trials actually used
• Retatrutide side effects by system and dose
• CagriSema vs tirzepatide vs retatrutide

-- The GLP-1 Daily Team