Retatrutide is the most searched-for peptide in the United States right now, and it isn't close. Over the past three months it has pulled roughly ten times the search interest of BPC-157, and it now sits level with semaglutide, a drug that has been on pharmacy shelves for years. Retatrutide is on no shelf anywhere. It is not approved, it cannot be lawfully bought, and the company that makes it spent August suing the people selling it.
So what is it, what has actually been proven, and what does the community's version of it have to do with the trials? Let's dive in.
TLDR
What is retatrutide? An investigational once-weekly injectable peptide from Eli Lilly (code LY3437943) that activates three receptors at once: GIP, GLP-1, and glucagon. The glucagon arm is what separates it from every approved drug in the class.
Results: In the published Phase 2 obesity trial, mean weight loss at 48 weeks was 24.2% on 12 mg. Lilly's unpublished Phase 3 toplines report 20.8% to 28.7% at 68 to 80 weeks. Only one Phase 3 trial has been published in a journal, and it was in people with type 2 diabetes.
Dosage: The trials started at 1 to 2 mg once weekly and stepped up every four weeks to 4, 9, or 12 mg. Community protocols run lower and slower. No evidence-based dosing guideline exists outside a trial.
Safety: Nausea, vomiting, and other GI effects are common and dose-related. Heart rate goes up. A skin-sensitivity signal is specific to this compound. Six cases of acute liver injury from products labelled as retatrutide have been recorded by an Australian health department, with a contaminant suspected rather than the molecule.
Legal Status (September 2026): Not approved anywhere. Lilly plans to file with the FDA in Q1 2027. Cannot be compounded under US federal law. Not on the WADA Prohibited List, though GLP-1 receptor agonists are on WADA's 2026 Monitoring Program.
What Is Retatrutide, and Why Is Everyone Suddenly Searching for It?
Retatrutide is a single lab-made peptide chain, built to survive in the body for about six days. Non-natural amino acids in the sequence resist the enzymes that would otherwise chew it up, and a fatty acid tail attached at position 17 binds to albumin in the blood, which is what stretches the half-life far enough for once-weekly injection (Urva et al., 2022, The Lancet, PMID 36354040).
Semaglutide hits one receptor. Tirzepatide hits two. Retatrutide hits three.
The reason it's everywhere right now comes down to three things that landed on top of each other this summer.
In May, Lilly announced the headline Phase 3 obesity result: 28.3% average weight loss at 80 weeks on the top dose. In July, two more Phase 3 trials read out and Lilly said it would file for FDA approval in the first quarter of 2027. And on August 12, Lilly filed six lawsuits against US businesses selling it, including four research-use-only peptide vendors, and said it had reported more than 200 entities to the FDA, the Department of Justice, and state attorneys general.
Weight-loss numbers nobody has seen before, a drug you can't legally get, and a manufacturer going to court over the vials being sold anyway. That's the whole story of why the search graph looks the way it does.
How Does Retatrutide Work?
One molecule, three receptors, and they do different jobs.
The GLP-1 and GIP receptor activity does what the approved drugs already do: slows stomach emptying, blunts appetite, and improves how the body handles glucose. Most of the weight loss from semaglutide and tirzepatide comes from people simply eating less.
The glucagon receptor arm is the new part. In obese animals, adding glucagon activity increased energy expenditure on top of the intake reduction from the other two receptors, and that is the design case for the third receptor (Coskun et al., 2022, Cell Metabolism, PMID 35985340). Retatrutide burns more as well as eats less, at least in mice.
It is not equally strong at all three. Measured against each receptor's natural hormone, retatrutide is roughly 0.3 times as potent as glucagon at the glucagon receptor, 0.4 times as potent as GLP-1 at the GLP-1 receptor, and 8.9 times as potent as GIP at the GIP receptor. It is heavily weighted toward GIP, with comparatively modest activity at the other two, and that balance was chosen deliberately.
Wait, doesn't glucagon raise blood sugar?
Yes. That's the obvious objection, and it deserves a straight answer.
Glucagon is the hormone that tells your liver to release glucose. Deliberately activating its receptor in a drug meant to lower blood sugar looks like a contradiction. In practice, the glucose-lowering from the GLP-1 and GIP arms more than covers it. No clinically significant hypoglycemia was reported at any dose in the Phase 2 obesity trial (Jastreboff et al., 2023, NEJM, PMID 37366315), and no severe hypoglycemia in either diabetes trial (Rosenstock et al., 2023, The Lancet, PMID 37385280; Bajaj et al., 2026, The Lancet, PMID 42250575).
The trials answered the objection. The theory didn't.
Retatrutide vs Tirzepatide vs Semaglutide: What's Actually Different
| Compound | Receptors | Status | Best published weight loss |
|---|---|---|---|
| Semaglutide | GLP-1 | Approved | ~15% at 68 weeks (STEP 1) |
| Tirzepatide | GIP + GLP-1 | Approved | ~21% at 72 weeks (SURMOUNT-1) |
| Retatrutide | GIP + GLP-1 + glucagon | Investigational | 24.2% at 48 weeks (Phase 2) |
Here's the caveat that gets dropped in almost every comparison you'll read: no randomized trial has ever compared retatrutide head-to-head against semaglutide or tirzepatide. Every "retatrutide beats tirzepatide" claim is built by putting numbers from separate trials, with different populations, durations, and endpoints, next to each other.
The closest thing to a fair comparison is a 2025 network meta-analysis pooling 19 trials and 29,506 adults (Sinha and Ghosal, 2025, Obesity, PMID 40685589). It ranked retatrutide with the highest odds of reaching 15% weight loss. It also ranked it with the highest adverse-event risk of any drug in the analysis. Those two findings travel together, and anyone quoting the first without the second is selling something.
(For the approved comparators, see our tirzepatide and semaglutide library entries.)
What the Phase 3 Data Actually Shows
This is where retatrutide coverage goes wrong most often, so we're going to be precise about it.
There is a difference between a trial that has been published in a peer-reviewed journal and a trial whose results have been announced in a company press release. The first can be inspected by anyone. The second is the sponsor's summary of its own unpublished data. It isn't dishonest, but it isn't peer review either.
What has been published
Phase 2, obesity (Jastreboff et al., 2023, NEJM, PMID 37366315). 338 adults with obesity and no diabetes, 48 weeks, placebo-controlled.
| Dose | 24 weeks | 48 weeks |
|---|---|---|
| Placebo | −1.6% | −2.1% |
| 1 mg | −7.2% | −8.7% |
| 4 mg | −12.9% | −17.1% |
| 8 mg | −17.3% | −22.8% |
| 12 mg | −17.5% | −24.2% |
At 12 mg, every single participant lost at least 5% of body weight, 93% lost at least 10%, and 83% lost at least 15%. Weight was still falling at week 48 in the higher-dose groups, which is why Phase 3 was designed to run 80 weeks.
Phase 2, type 2 diabetes (Rosenstock et al., 2023, The Lancet, PMID 37385280). 281 adults, 36 weeks, with dulaglutide as an active comparator. Weight fell 16.9% on 12 mg against 2.0% on dulaglutide. Against an actual GLP-1 drug rather than placebo, the gap was roughly eightfold.
Phase 2a liver-fat substudy (Sanyal et al., 2024, Nature Medicine, PMID 38858523). In 98 participants with fatty liver disease, liver fat fell 82.4% at 24 weeks on 12 mg. 86% of that group reached a normal liver-fat level. Placebo: none.
Phase 3, type 2 diabetes (Bajaj et al., 2026, The Lancet, PMID 42250575). This is the only Phase 3 trial in a journal. 537 adults, 40 weeks. HbA1c fell 1.94 points on 12 mg against 0.81 on placebo; weight fell 15.3% against 2.6%. Discontinuation for side effects ran 2 to 5%.
What has not been published
The four TRIUMPH obesity trials, the ones producing the numbers everybody quotes.
| Trial | Population | Reported result | Status |
|---|---|---|---|
| TRIUMPH-4 | Obesity + knee osteoarthritis | −28.7% at 68 weeks, 12 mg | Topline, Dec 2025 |
| TRIUMPH-1 | Obesity, no diabetes | −28.3% at 80 weeks, 12 mg | Topline, May 2026 |
| TRIUMPH-2 | Obesity + type 2 diabetes | −20.8% at 80 weeks | Topline, Jul 2026 |
| TRIUMPH-3 | Severe obesity + cardiovascular disease | −22.6% at 80 weeks | Topline, Jul 2026 |
In TRIUMPH-1, Lilly also reported that 45.3% of participants on 12 mg lost at least 30% of their body weight. That is an extraordinary figure. It is also, as of today, a figure in a press release.
The 28% number is real in the sense that Lilly reported it. It is unverified in the sense that nobody outside Lilly has seen the methods, the full safety tables, or the dropout analysis. Until the papers appear, treat it as a strong company claim, not as settled evidence.
One more gap worth naming: every published retatrutide trial was funded by Eli Lilly, and Lilly employees are co-authors on all of them. That's normal at this stage of development. It's still a limitation.
Retatrutide Dosage: What the Trials Used vs What the Community Does
Let's be clear about what exists. There is a trial titration schedule, which is documented. And there is community practice, which is a set of protocols people have converged on without any validation. They are not the same thing, and neither is a guideline.
The trial schedule
Phase 2 tested 1, 4, 8, and 12 mg once weekly. Phase 3 narrowed that to 4, 9, and 12 mg. Every schedule started low and escalated: in TRIUMPH-1, participants began at 2 mg weekly and stepped up every four weeks until they reached their assigned dose.
The escalation matters more than it looks. The Phase 2 obesity trial ran two of its dose groups twice, once starting at 2 mg and once starting at 4 mg. Gastrointestinal side effects were partially mitigated by the lower starting dose (Jastreboff et al., 2023). How fast you get to a dose changes how well you tolerate it, independently of the dose itself.
What the community reports
Community protocols are conservative compared to the trials, and that's probably the right instinct given what's in the vials. Commonly reported starting doses are 0.5 to 1 mg once weekly, held for three to four weeks before stepping up, with most people describing a ceiling of 4 to 8 mg rather than the trial maximum of 12 mg.
A 2026 preprint analysed self-reported side effects from 13,589 Reddit users taking unapproved retatrutide (Sehgal et al., 2026, medRxiv). It's not peer reviewed, and it measures what people write, not what was in their syringe. But it's the only dataset of any size that exists on community use, and it's worth knowing it's there.
None of this is a recommendation. It's a description of what people are doing, in a situation where no validated protocol exists outside a clinical trial.
Reconstitution math
This is the practical question behind one of the fastest-rising retatrutide searches right now ("how much bac water for 30mg retatrutide"), so here is the arithmetic.
Retatrutide on the gray market is typically sold as 10 mg, 20 mg, or 30 mg of lyophilized powder. The concentration you end up with is the vial strength divided by the volume of bacteriostatic water you add.
| Vial | BAC water added | Concentration | 1 mg dose on a U-100 syringe |
|---|---|---|---|
| 10 mg | 2 mL | 5 mg/mL | 0.2 mL = 20 units |
| 20 mg | 2 mL | 10 mg/mL | 0.1 mL = 10 units |
| 30 mg | 3 mL | 10 mg/mL | 0.1 mL = 10 units |
At 10 mg/mL, a 2 mg dose is 20 units and a 4 mg dose is 40 units. Double-check your own vial and water volume with our reconstitution calculator and dosage calculator rather than trusting a table.
Two handling notes from the FDA's guidance on this drug class: a multi-dose vial should be discarded 28 days after first puncture regardless of what the seller's instructions say, and an injectable that arrives warm should not be used.
Retatrutide Side Effects: What the Trials Recorded
Gastrointestinal effects
Common, dose-related, and the main reason people quit. In the Phase 2 obesity trial, nausea reached 60% in the highest-exposure group against 11% on placebo. Vomiting hit 26% against 1%. Diarrhea 20%, constipation 16%. Discontinuation due to side effects ran between 6% and 16% across the retatrutide groups, against zero on placebo (Jastreboff et al., 2023).
Heart rate
Heart rate rose in a dose-dependent way, peaked around week 24, then declined by week 48. A composite category covering arrhythmias and conduction disorders was recorded in 6% of participants overall, reaching 14% in one dose group. This is the finding most plausibly tied to the glucagon arm, since both GLP-1 and glucagon receptor activity raise heart rate. It is also the finding a 48-week trial in 338 people is least equipped to characterise.
Skin sensitivity
An unusual one, and specific to this compound. Cutaneous hyperesthesia and skin-sensitivity events were reported in 7% of retatrutide recipients against 1% on placebo. None were serious, none had visible skin findings, and none led to discontinuation. There is no established mechanism. If you're on it and your skin feels strange, this is why.
Pancreas, gallbladder, and liver
One serious case of acute pancreatitis in the 12 mg group and three biliary events across the Phase 2 obesity trial. Small numbers in a small trial, so they neither establish nor rule out a class effect. Transient liver-enzyme elevation above three times normal occurred in 1% of participants, and mean liver enzymes were unchanged or lower at 48 weeks.
The liver-injury alert you need to know about
On June 19, 2026, the Chief Health Officer of Victoria, Australia issued a health alert recording six cases of acute liver injury since January in people who had used unapproved products labelled as retatrutide, bought online and through social media. Presentation was fatigue, jaundice, abdominal pain, dark urine, and abnormal bruising.
Read it carefully. The alert says the toxicity is possibly associated with a contaminant in the products, not with retatrutide itself, and the contaminant had not been identified at the time of the alert. So: six confirmed liver injuries, a suspected contaminant, and no published chemistry. Anyone citing this as proof that retatrutide damages the liver is overreading it. Anyone dismissing it because the contaminant wasn't named is underreading it.
The trial safety record describes the molecule. The health alert describes what's in an unverified vial. Those are two different things, and the second one is what you'd actually be injecting.
What happens when you stop?
Nobody knows. There is no retatrutide withdrawal or maintenance trial, of the kind that exists for semaglutide (STEP 4) and tirzepatide (SURMOUNT-4). Both of those showed substantial regain after stopping. Expecting the same from retatrutide is reasonable. It is not a finding.
Why Eli Lilly Is Suing Peptide Vendors
On August 12, 2026, Lilly filed six lawsuits in US federal courts against businesses selling retatrutide: a Texas compounding pharmacy, a California med-spa chain, and four Texas online peptide sellers. It's the first time Lilly has gone after research-use-only vendors directly rather than compounders and telehealth companies.
The numbers in the announcement are the useful part. Lilly said it has reported more than 14,000 websites, ads, social posts, and product listings across more than 100 countries, and referred more than 200 individuals and entities to the FDA, the DOJ, state attorneys general, and licensing boards. Lilly obviously has a commercial interest in this, and that belongs next to the quote. It doesn't change the underlying facts, which come from the regulator.
Why "research use only" doesn't protect anyone
The FDA has stated plainly that retatrutide cannot be used in compounding under federal law, is not a component of any approved drug, and has not been found safe and effective for any condition. There is no shortage-list loophole, because a shortage is a shortage of an approved product, and retatrutide has never been approved.
The RUO label has now been tested against the FDA and lost. In a March 2026 warning letter to a peptide vendor, the agency wrote that despite the "research use only" labelling, the seller's own product copy about appetite suppression, insulin sensitivity, and fat oxidation established that the products were intended as drugs for human use. The disclaimer and the sales pitch sat on the same page, and the FDA read the page as a whole.
The agency has also added retatrutide to Import Alert 66-80, which lets it detain shipments of GLP-1 active ingredients at the border without physical examination. That tells you where the powder is coming from: bulk API from overseas manufacturers, screened at the manufacturer level, not the vial level.
The Lilly-FDA dispute you haven't heard about
There's a second legal thread. Lilly and the FDA have been arguing since 2024 over whether retatrutide is a biologic or a small-molecule drug. It sounds academic. It isn't: a Biologics License Application comes with 12 years of market exclusivity, a standard New Drug Application with five. That dispute is coming to a head as the Q1 2027 filing approaches, and it will shape how long Lilly holds the market once it's approved.
For the full enforcement record, the warning-letter table, and what a certificate of analysis can and can't tell you, see our retatrutide sourcing and quality page.
The Honest Take
Retatrutide is probably the most effective weight-loss compound ever tested in humans. The published Phase 2 data is strong, the mechanism is coherent, and the unpublished Phase 3 numbers, if they hold up in print, are unlike anything else in the class.
It is also a drug with no approved product, no reference standard, one manufacturer that doesn't sell it, and a gray market that has already produced six liver injuries from a contaminant nobody has identified. The trial record and the black-market record are describing different things, and only one of them is available to you.
If you're waiting for it: the FDA filing is Q1 2027, which puts a decision somewhere in late 2027 or 2028. If you're not waiting: understand that every safety figure in this article was measured on a molecule you can't get, not on the one in the vial.
FAQ
What is retatrutide?
An investigational once-weekly injectable peptide from Eli Lilly that activates the GIP, GLP-1, and glucagon receptors. It's in Phase 3 trials and not approved anywhere.
How much weight do people lose on retatrutide?
In the published Phase 2 trial, 24.2% at 48 weeks on 12 mg. Lilly's unpublished Phase 3 toplines report 20.8% to 28.7% at 68 to 80 weeks.
Is retatrutide better than tirzepatide?
Nobody knows. No head-to-head trial has been run. Indirect comparisons favour retatrutide for weight loss and also rank it highest for adverse events.
What is the retatrutide dose?
Trials used 4, 9, or 12 mg once weekly, reached by starting at 1 to 2 mg and stepping up every four weeks. There is no validated dose outside a trial.
How much bacteriostatic water for a 30 mg retatrutide vial?
3 mL gives 10 mg/mL, so 1 mg is 10 units on a U-100 insulin syringe. Check your own numbers with the reconstitution calculator.
What are the side effects of retatrutide?
Nausea, vomiting, diarrhea, and constipation are the most common. Heart rate increases. Skin sensitivity was reported in 7% of trial participants. Rare pancreatitis and gallbladder events were recorded.
Does retatrutide cause liver damage?
The trials found no liver-toxicity signal. Six cases of acute liver injury have been linked to gray-market products labelled as retatrutide, with a contaminant suspected rather than the compound.
Is retatrutide legal?
It is not approved for human use in any country and cannot be compounded under US law. Lilly plans to file with the FDA in Q1 2027.
Is retatrutide banned by WADA?
It is not on the 2026 Prohibited List. GLP-1 receptor agonists are on WADA's 2026 Monitoring Program, which means usage is being tracked ahead of any decision.
When will retatrutide be approved?
Lilly has said it will submit to the FDA in the first quarter of 2027. A standard review would put a decision in late 2027 or 2028.
What happens when you stop taking retatrutide?
No study has looked at it. Semaglutide and tirzepatide both show substantial regain after stopping, and there's no reason to expect retatrutide to be different.
Resources
Jastreboff et al. (2023), NEJM, Phase 2 obesity — https://pubmed.ncbi.nlm.nih.gov/37366315/
Rosenstock et al. (2023), The Lancet, Phase 2 type 2 diabetes — https://pubmed.ncbi.nlm.nih.gov/37385280/
Sanyal et al. (2024), Nature Medicine, liver-fat substudy — https://pubmed.ncbi.nlm.nih.gov/38858523/
Bajaj et al. (2026), The Lancet, TRANSCEND-T2D-1 Phase 3 — https://pubmed.ncbi.nlm.nih.gov/42250575/
Coskun et al. (2025), Lancet Diabetes & Endocrinology, body-composition substudy — https://pubmed.ncbi.nlm.nih.gov/40609566/
Coskun et al. (2022), Cell Metabolism, discovery and mechanism — https://pubmed.ncbi.nlm.nih.gov/35985340/
Urva et al. (2022), The Lancet, Phase 1b — https://pubmed.ncbi.nlm.nih.gov/36354040/
Giblin et al. (2026), Diabetes, Obesity and Metabolism, TRIUMPH program design — https://pubmed.ncbi.nlm.nih.gov/41090431/
Sinha and Ghosal (2025), Obesity, network meta-analysis — https://pubmed.ncbi.nlm.nih.gov/40685589/
Sehgal et al. (2026), medRxiv preprint, Reddit self-reports — https://doi.org/10.64898/2026.05.28.26352819
Eli Lilly, press release on Phase 3 results and FDA filing plan (July 23, 2026), via CNBC — https://www.cnbc.com/2026/07/23/eli-lilly-will-file-for-approval-of-retatrutide-obesity-drug-in-2027.html
Eli Lilly, lawsuits and black-market statement (August 12, 2026) — https://investor.lilly.com/news-releases/news-release-details/lilly-calls-online-platforms-payment-companies-and-regulators
NPR, coverage of the six lawsuits (August 13, 2026) — https://www.npr.org/2026/08/13/g-s1-138594/eli-lilly-files-6-lawsuits-against-businesses-selling-black-market-obesity-drug
BioSpace, the Lilly-FDA biologic classification dispute — https://www.biospace.com/fda/lilly-fda-retatrutide-biologic-dispute-comes-to-a-head-as-submission-nears
FDA, concerns with unapproved GLP-1 drugs — https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
Victoria Department of Health, liver-injury alert (June 19, 2026) — https://www.health.vic.gov.au/health-alerts/toxicity-linked-to-unapproved-peptide-product-labelled-retatrutide
ClinicalTrials.gov, TRIUMPH-Outcomes NCT06383390 — https://clinicaltrials.gov/study/NCT06383390
WADA 2026 Prohibited List — https://www.wada-ama.org/en/resources/2026-prohibited-list
WADA 2026 Monitoring Program — https://www.wada-ama.org/en/resources/2026-monitoring-program