Retatrutide: Weight Loss Results, Dosage, FDA Status (2026)

Retatrutide is Lilly’s triple-agonist peptide, hitting GIP, GLP-1, and glucagon receptors from one weekly injection. In the pivotal TRIUMPH-1 trial, the 12mg arm lost an average of 70.3 lb, or 28.3% of body weight, over 80 weeks. That’s the largest weight loss any drug has produced in a Phase 3 obesity trial, and it’s why searches for retatrutide dosage, side effects, and retatrutide vs tirzepatide have exploded.

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It’s also not for sale. No brand name, no pharmacy pen, no approval. Lilly says it will file with the FDA in the first quarter of 2027. Medical sites walk the trial data and stop at “you can’t buy it.” This guide covers the Lilly file in full and then keeps going into the research-vial market, where the same molecule is sold under catalog names like GLP-3 R, because that’s where most people reading this end up. Updated September 2026.

If you’re sourcing a research vial, Paramount Peptides’ GLP-3 R is retatrutide (CAS 2381089-83-2, the 39-amino-acid triple agonist), synthesized in-house in Irvine, California, in 12mg, 24mg, and 60mg vials from $170 with a COA on the listing. Code BRAINFLOW takes 10% off.

What Retatrutide Is

Retatrutide is a synthetic 39-amino-acid peptide engineered by Eli Lilly to activate three receptors at once: GIP, GLP-1, and glucagon. Its development code is LY3437943 and its CAS number is 2381089-83-2. It’s an injectable, not a tablet like Lilly’s oral GLP-1 orforglipron (Foundayo), and it’s dosed once a week under the skin, the same way Wegovy and Zepbound are.

Wegovy and Zepbound are peptides too. The difference is that they have a label and a pen, and retatrutide has a Phase 3 file and a freeze-dried powder in a research vial. Same drug class, very different legal status, which the FDA section below covers.

Why research vendors call it GLP-3

Search a research-peptide catalog for retatrutide and you often won’t find it under that name. Vendors list it as GLP-3, GLP-3 R, GLP-3 RT, or Reta. The “3” is shorthand for three receptors, and the naming keeps the trademarked development name off the listing. When a vendor’s page shows CAS 2381089-83-2 and a 39-amino-acid sequence, it’s retatrutide. If those identifiers aren’t on the page, you don’t know what you’re buying.

What Retatrutide Is Being Developed For

Lilly’s lead indication is obesity and overweight with at least one weight-related condition. The Phase 3 program, called TRIUMPH, also ran dedicated trials in type 2 diabetes (TRIUMPH-2), established cardiovascular disease (TRIUMPH-3), and knee osteoarthritis (TRIUMPH-4). A liver-fat substudy in people with MASLD has already published. Obstructive sleep apnea, chronic low-back pain, and a long cardiovascular outcomes trial are still running.

There is no labeled indication yet. In 2026, “used for” means “studied for.” People on the research market are running it as a weight-loss peptide, and that’s not a prescription use of anything.

How Retatrutide Works

Each of the three receptors does a different job, and the third one is what separates retatrutide from everything on pharmacy shelves.

GLP-1 slows stomach emptying and raises satiety, which is the whole mechanism of semaglutide (Wegovy, Ozempic). GIP is the second incretin, and adding it is what let tirzepatide (Zepbound, Mounjaro) beat semaglutide head to head in SURMOUNT-5. Glucagon is the third lock. Activating the glucagon receptor raises energy expenditure and changes how the liver handles fat, which is why the Phase 2 weight curve hadn’t flattened at week 48 and why the liver-fat numbers look different from a pure GLP-1.

The glucagon arm is also why resting heart rate drifted up in the trials, peaked around week 24, and then eased. It’s a feature and a cost in the same molecule.

Retatrutide Benefits and Weight Loss Results

Every figure here comes from Lilly’s Phase 3 announcements or the published Phase 2 papers. Nothing is extrapolated.

• Body weight. TRIUMPH-1, 12mg, 80 weeks: 28.3%, 70.3 lb from a 248.5 lb baseline. 45.3% of that arm lost 30% or more. In the BMI 35+ extension, 30.3% and 85.0 lb at 104 weeks.
• BMI class. 65.3% of the 12mg arm finished under a BMI of 30. Among people who started at BMI 40 or higher, 37.5% did the same.
• Cardiometabolic markers. TRIUMPH-3 (cardiovascular disease), 12mg: triglycerides down 37.0%, non-HDL cholesterol down 16.5%, systolic blood pressure down 9.3 mmHg, waist down 7.5 inches, hsCRP down 51.2%.
• Blood sugar. TRIUMPH-2 (type 2 diabetes): A1C fell 1.5 points at 12mg and 1.6 at 9mg. Weight fell 20.8%, or 49.6 lb.
• Knee osteoarthritis. TRIUMPH-4: 28.7% at 12mg over 68 weeks, with pain and function scores improving alongside the weight.
• Liver fat. Phase 2a MASLD substudy: relative liver fat down 86% at 12mg by 48 weeks.

What isn’t proven yet is fewer heart attacks and strokes. The outcomes trial that answers that runs into 2028 or 2029.

Retatrutide Clinical Trials

The Phase 2 trial, published by Jastreboff and colleagues in NEJM in 2023 (NCT04881760), enrolled 338 adults for 48 weeks. The 12mg arm lost 24.2%, and every single participant on that dose lost at least 5%. That paper is what turned retatrutide from a pipeline codename into the most anticipated obesity drug in development.

TRIUMPH-1, announced by Lilly on May 21, 2026 (NCT05929066), randomized 2,339 adults without diabetes for 80 weeks. Results by dose: 4mg lost 19.0% (47.2 lb), 9mg lost 25.9% (64.4 lb), 12mg lost 28.3% (70.3 lb). Placebo lost 2.2%. A 532-person subset with BMI 35 or higher continued to 104 weeks and kept losing.

TRIUMPH-2 and TRIUMPH-3 read out together on July 23, 2026. TRIUMPH-2 (NCT05929079) covered type 2 diabetes with obesity: 12mg lost 20.8%. TRIUMPH-3 (NCT05882045) covered severe obesity with established cardiovascular disease: 12mg lost 22.6%, or 55.8 lb. TRIUMPH-4 (NCT05931367), the knee osteoarthritis trial, reported in December 2025 at 28.7%. TRIUMPH-5 (NCT06662383), the head-to-head against tirzepatide, hasn’t reported.

Read the diabetes number carefully before assuming it’s a weaker drug in that group. People with type 2 diabetes lose less on every GLP-1 class drug, and 20.8% in that population is above what tirzepatide posted in its own diabetes trial.

Retatrutide and Liver Fat

The liver-fat result is the one that gets under-covered. Sanyal and colleagues, Nature Medicine 2024, took 98 people from the same Phase 2 cohort who started with liver fat of 10% or more. At 24 weeks, the 12mg group had cut relative liver fat by 82.4%. At 48 weeks, 86.0%. By week 24, 86% of that arm had normal liver fat (under 5%). In the placebo group, nobody did.

That’s the largest published liver-fat reduction in this drug class. It wasn’t a MASH-outcomes trial, so it doesn’t prove reversal of fibrosis or fewer liver events, but it’s the clearest signal yet that the glucagon receptor is doing something in the liver that GLP-1 alone doesn’t.

Retatrutide vs Tirzepatide, Wegovy, and Foundayo

Comparing across trials, retatrutide looks ahead of tirzepatide by roughly seven percentage points at the top dose. That’s not a head-to-head, and cross-trial comparisons flatter whichever drug had the more favorable population. TRIUMPH-5 (NCT06662383) is the direct comparison against tirzepatide, and it hasn’t read out. Until it does, “better than Zepbound” is a strong inference, not a result.

Foundayo is a different product for a different patient. It’s Lilly’s oral GLP-1, aimed at people who won’t inject, and its weight loss sits below the injectables. Nobody picks Wegovy over retatrutide for the ceiling. They pick it because a pharmacy will fill it this week.

One practical note for people switching. Coming off Mounjaro or Zepbound, community practice lands at 2 to 4mg of retatrutide rather than restarting at the bottom. People with no GLP-1 history are the 0.5 to 1mg crowd. The trial protocol started everyone at 2mg.

Retatrutide Dosage and Reconstitution

Once weekly, same day each week, subcutaneous. The half-life is about six days, which is what makes weekly dosing work. Phase 3 started at 2mg and stepped up every four weeks: 2, 4, 6, 9, then 12. The forum chart most people screenshot runs 1, 2, 4, 8, 12, with a 0.5mg entry rung for anyone nervous about the gut. Hold a rung if nausea hasn’t settled. Stepping up on schedule regardless of how you feel is how people ended up in the discontinuation column.

None of this is approved dosing. It’s what the trials did and what the community copies. The maximum-tolerated-dose logic from the trials applies: 9mg did nearly as well as 12mg in TRIUMPH-1 (25.9% vs 28.3%) with fewer dropouts (6.9% vs 11.3%), so plenty of people never need the top rung.

Reconstitution math for 12mg, 24mg, and 60mg vials

Add 3 mL of bacteriostatic water to any of the three sizes and the numbers stay clean. On a U-100 insulin syringe, 100 units is 1 mL.

Which size to buy depends on where you are on the ladder. The forum ladder uses 12mg total across weeks 1 to 8 (four weeks at 1mg, four at 2mg), so a 12mg vial covers that phase exactly and gets used up inside the stability window. The 60mg vial covers the full 16-week forum ladder (60mg total) or five weeks at 12mg maintenance, and it’s the one to buy once you’re past 4mg.

The 24mg sits between them. At $459 with the code, the 60mg works out to about $7.65 per milligram, against $12.75 for the 12mg at $153.

Storage and handling

Unmixed, the freeze-dried powder keeps for months in the refrigerator and longer in the freezer, kept dark. A few days at room temperature in transit doesn’t hurt it. Once you add bacteriostatic water, refrigerate at 2 to 8 C, never freeze it, and treat four weeks as the working window. Draw your dose and put the vial straight back. If it goes cloudy or grows particles, it’s done.

Inject subcutaneously into the fat of the abdomen (two inches from the navel), the outer thigh, or the upper arm, with a 29 to 31 gauge insulin syringe. Rotate sites week to week. Same day each week, any time of day, with or without food.

Who it’s for, and who should wait

The trial populations were adults with obesity, or overweight plus a weight-related condition, and the people who did best were the ones who tolerated the full ladder. Anyone who’s already on tirzepatide and losing steadily has little reason to switch before TRIUMPH-5 reads out.

Anyone with the class contraindications in the side-effects section shouldn’t be on any of these drugs. And anyone who wants a labeled product with a prescriber behind it should wait for 2027 or 2028, because that’s when this stops being a research chemical.

How Long Does Retatrutide Take to Work?

Appetite usually changes in the first two to four weeks, often within days of the first injection. Scale weight is a months-long slope. Phase 2 already showed double-digit percentage loss by week 24 at the higher doses, TRIUMPH-1 kept falling through week 80, and the BMI 35+ extension was still adding loss at week 104.

If the question is “will I feel it this week,” the answer is yes, in the gut and at the fork. If the question is “when do I hit the 70-pound headline,” that took 80 weeks at the top dose in a supervised trial, and half the arm didn’t get there.

Retatrutide Side Effects

The side-effect profile is the GLP-1 class profile with the volume turned up. In TRIUMPH-1 at 12mg, nausea hit 42.4% (placebo 14.8%), diarrhea 32.0% (13.5%), constipation 26.1% (10.9%), and vomiting 25.3% (4.8%). Almost all of it clustered after a dose step-up and eased within a couple of weeks.

The number that matters most is who quit. Discontinuation for adverse events in TRIUMPH-1 was 4.1% at 4mg, 6.9% at 9mg, and 11.3% at 12mg, against 4.9% on placebo. TRIUMPH-2 at 12mg was 7.7%. TRIUMPH-3, the cardiovascular population, was 13.5%. That’s the price of the 28% number, and it’s the argument for the slow ladder.

Two effects are specific to this molecule. Resting heart rate drifted up, peaked around week 24, then eased, which traces to the glucagon receptor. And dysesthesia, an odd skin or nerve buzzing, showed up more than with pure GLP-1s. Mild urinary tract infections were also reported. None of those commonly ended trial participation.

The class cautions apply in full. Personal or family history of medullary thyroid carcinoma or MEN2, a prior serious reaction to a GLP-1 drug, and pregnancy are hard stops. A history of pancreatitis, significant gastroparesis, active gallbladder disease, or impaired kidney function is a conversation with a clinician, not a forum poll.

Retatrutide also falls under WADA’s S0 category for non-approved substances, so tested athletes should treat it as prohibited.

FDA Status, Cost, and When Retatrutide Will Be Available

Retatrutide is not FDA-approved and has no trade name. In its July 23, 2026 release, Lilly said it plans to submit a Biologics License Application in the first quarter of 2027. If that holds and the FDA takes a standard review, a decision lands in late 2027 or 2028. There is no commercial price because there is no commercial product.

Compounding pharmacies cannot make it. Compounding a drug requires either an approved product in shortage or a substance on the FDA’s bulk list, and retatrutide is neither. The FDA sent warning letters in September 2025 to sellers marketing it with treatment claims. Anything sold as “compounded retatrutide” is operating outside those rules.

Research vials are a separate market with separate rules. They’re sold for laboratory use, priced per milligram rather than per month, and they come with a certificate of analysis instead of a label. That’s the $170-to-$510 conversation in the next section, not a list price from Lilly.

Where to Buy Retatrutide (GLP-3 R) as a Research Peptide

No chromatogram, no purchase. With a 39-amino-acid peptide there’s a lot of room for a bad synthesis, and the research market has more sellers than labs. Two things make a listing trustworthy. The identifiers match retatrutide (CAS 2381089-83-2, 39 amino acids, triple agonist), and a lot-specific COA from a named lab is on the page.

Paramount Peptides lists it as GLP-3 R, with the CAS number and sequence on the page. They’ve synthesized their own peptides in Irvine, California for over 12 years, which for a molecule this long is the difference between a lab that ran the chemistry and a reseller that opened a box. Purity is 99% or better by HPLC, the COA loads when you select a dose, and if a vial ever fails HPLC at a licensed lab they refund the order and your $100 testing fee.

Three sizes, public pricing, standard card checkout: 12mg for $170, 24mg for $340, 60mg for $510. Code BRAINFLOW takes 10% off any of them, and orders over $300 ship free, which the 24mg and 60mg both clear.

Retatrutide FAQ

Is retatrutide FDA approved?

No. Lilly plans to file a BLA in the first quarter of 2027, which puts a decision in late 2027 or 2028. It has no brand name and no pharmacy availability.

Is retatrutide a GLP-1?

Partly. It activates the GLP-1 receptor plus GIP and glucagon receptors. Calling it “a GLP-1” describes one third of the molecule. The glucagon activity is what makes it different.

Is retatrutide the same as Ozempic or Mounjaro?

No. Ozempic is semaglutide, a single GLP-1 agonist. Mounjaro is tirzepatide, a GIP plus GLP-1 dual agonist. Retatrutide adds glucagon on top of both, and unlike either of them it isn’t approved.

How much weight can you lose on retatrutide?

TRIUMPH-1’s 12mg arm averaged 70.3 lb, or 28.3%, at 80 weeks, and 45.3% of that arm lost 30% or more. The BMI 35+ extension averaged 85.0 lb at 104 weeks. In type 2 diabetes the average was 20.8%.

How long does retatrutide take to work?

Appetite changes inside the first few weeks. The headline weight numbers took 80 weeks at the top dose. Expect a steady slope rather than a fast drop.

Retatrutide vs tirzepatide: which is stronger?

Across separate trials, retatrutide’s 28.3% beats tirzepatide’s roughly 21% by a wide margin. The direct comparison, TRIUMPH-5, hasn’t reported, so that’s an inference from different populations rather than a head-to-head result.

What is the retatrutide dosage?

The Phase 3 protocol started at 2mg weekly and stepped every four weeks to 4, 6, 9, and 12mg. Community protocols start lower, at 0.5 to 1mg, and step through 2, 4, 8, and 12. None of it is approved dosing.

What are the worst retatrutide side effects?

Nausea, vomiting, diarrhea, and constipation, worst right after a dose increase. At 12mg in TRIUMPH-1, 42.4% had nausea and 11.3% quit the trial for side effects. Heart rate rises through about week 24, and some people report nerve or skin buzzing.

What is GLP-3 R?

A catalog name for research-grade retatrutide. The “3” refers to three receptors. Confirm the listing shows CAS 2381089-83-2 and a 39-amino-acid sequence before assuming a GLP-3 product is retatrutide.

Where can I buy retatrutide?

Not from a pharmacy, and not compounded. As a research peptide, BrainFlow points readers to Paramount Peptides GLP-3 R, synthesized in-house in California, with the CAS number and COA on the listing, in 12mg, 24mg, and 60mg vials from $170. Code BRAINFLOW takes 10% off. Sold for research use only.

What to Make of Retatrutide in 2026

70.3 lb at 80 weeks is the number that will define this drug. The liver-fat result is the one that will matter more in ten years. The glucagon receptor is the reason both exist, and it’s also the reason one in nine people on the top dose walked away from the trial.

For now it’s a research chemical in the United States, and it will stay one until at least late 2027. If you’re sourcing it that way, buy from a lab that made it, mix milligrams rather than whole vials, climb the ladder slower than you think you need to, and let the gut decide when to step up.

Paramount Peptides GLP-3 R, 12mg, 24mg, and 60mg. Code BRAINFLOW saves 10%.

Sources

• Jastreboff AM, et al. “Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial.” NEJM, 2023. NCT04881760. NEJM
• Sanyal AJ, et al. “Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial.” Nature Medicine, 2024. Nature Medicine
• Eli Lilly. “Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial.” May 21, 2026. TRIUMPH-1, NCT05929066. Lilly
• Eli Lilly. “Lilly’s triple agonist, retatrutide, successful in two additional Phase 3 obesity trials.” July 23, 2026. TRIUMPH-2, NCT05929079; TRIUMPH-3, NCT05882045. Lilly
• Eli Lilly. TRIUMPH-4 knee osteoarthritis topline results, December 2025. NCT05931367.
• ClinicalTrials.gov. TRIUMPH-5, retatrutide versus tirzepatide. NCT06662383.

Retatrutide is investigational and not FDA-approved for any indication. Trial figures are from Lilly’s announcements and peer-reviewed publications as cited. All information here is for educational and research purposes only and is not medical advice.

Research-grade retatrutide is sold for laboratory use only and cannot be legally compounded by a pharmacy. Amounts described come from trial protocols and community reports as context, not as instructions. Consult a qualified healthcare provider before beginning any protocol.

This article contains affiliate links. BrainFlow may earn a commission on qualifying purchases at no additional cost to the reader. We only recommend sources we trust.

Last updated September 2026.