Retatrutide (LY3437943)
Retatrutide: What The Studies Actually Say
You have seen 28% and 30%. Nobody outside the company ever checked those numbers. Here is what the published trial actually found.
Updated 20 September 2026
Before you read this
This page explains what published studies found. That is all it is. It is not medical advice, and it is not instructions for using anything. Nothing here is meant to find, treat, cure or stop any illness. The compounds discussed on this site, retatrutide included, are not approved by the FDA for use in people. Research compounds are sold for laboratory use only — not for use in humans or animals. A study tells you what happened to the people in it. It does not tell you what would happen to you. What you do with what you read here is your responsibility, so talk to a doctor first. This page is published by Ascend Vials, which sells research compounds.
Read the full guide
Confirm you have read the notice above and enter an email address. We will send you a link back to this guide, and sometimes an email when we publish a new one. You can unsubscribe any time.
Most of what you have heard about retatrutide came from a press release, not a study.
Here is what the actual research found. Every claim has a link. Read them yourself.
The 30-second version
- The best published study showed 24% average weight loss in 48 weeks at the top dose.
- On paper it beats Wegovy and Zepbound — but in a much smaller, shorter study.
- The famous bigger numbers — 28%, 30% — are company press releases, not published studies.
- About 1 in 6 people quit at the top dose because of how it made them feel.
- It is not approved anywhere. Lilly plans to ask the FDA in early 2027.
- Nothing sold online has been shown to match what the trials used. No study has checked.
The numbers, from the real study
The best published study followed 338 adults for 48 weeks. About 1 in 5 got a fake shot so the results could be compared. New England Journal of Medicine, 2023
At the top dose, 93% of people lost more than a tenth of their body weight. Blood pressure and blood sugar improved. So did most cholesterol numbers — but HDL, the good kind, did not change. Of the people who started with prediabetes, 72% had normal blood sugar at the end. On the fake shot, 22% did too. One reading is not a cure, and nobody followed them after the study stopped.
Everyone in the study also met with a dietitian.
How it compares to Ozempic and Mounjaro
You know them as Ozempic and Mounjaro. For weight loss the approved versions are called Wegovy and Zepbound — same drugs, different names. Those are the versions that were studied. Here are the real published numbers.
| Retatrutide | Wegovy | Zepbound | |
|---|---|---|---|
| Weight loss | −24.2% | −14.9% | −20.9% |
| Study length | 48 weeks | 68 weeks | 72 weeks |
| People studied | 338 | 1,961 | 2,539 |
| Quit from side effects (top dose) | 16% | 7% | 6% |
| FDA approved | No | Yes, 2021 | Yes, 2023 |
Read the whole table. Everything under that first number matters just as much.
Retatrutide's number is the biggest. It also comes from a study with 338 people, while the other two had nearly 2,000 and over 2,500. It ran 48 weeks against their 68 and 72. And it is an earlier stage of testing — the stage before the big trials that decide whether a drug gets approved.
These were also three separate studies, run at different times in different groups of people. Two of them — Zepbound's and retatrutide's — were run by the same company, Eli Lilly. No head-to-head trial of these drugs has ever been published. Two are running right now. Neither has reported. So this table shows what each one did in its own study — not what would happen if they competed.
Sources: STEP 1, NEJM 2021 · SURMOUNT-1, NEJM 2022 · Retatrutide, NEJM 2023
The famous numbers were never checked by anyone
You have seen bigger figures. 28%. 30%. Those came from Eli Lilly press releases, not studies. No journal has published them. No outside scientist has reviewed them.
Only one late-stage study has been published. It ran 40 weeks in people with type 2 diabetes and showed 11% to 15% weight loss. Lancet, 2026
So the honest line is this: the longest published, peer-reviewed research is 48 weeks. Everything past that is a company talking about itself. It may turn out to be true. It just has not been checked yet.
What it is
Retatrutide is a lab-made peptide from Eli Lilly.
It works on three body receptors at once: GIP, GLP-1 and glucagon. Semaglutide — the drug in Ozempic and Wegovy — works on one. Tirzepatide — the drug in Mounjaro and Zepbound — works on two. That third one is the whole idea — it is meant to make the body burn more energy, not just eat less.
In the studies people got one shot a week. That is because the body clears only about half of one dose in six days. Source
The part that makes it different was only shown in mice
That burn-more-energy part has never been tested in a person. It comes from a study in mice. The human studies measured weight, body fat, blood sugar and liver fat. They never checked whether the body was burning more energy. So the one thing that is supposed to set this drug apart from the others is still an idea. Source
What to expect
Stomach problems are the main story, and they climb with the dose.
| Placebo | 12 mg | |
|---|---|---|
| Nausea | 11% | 45% |
| Throwing up | 1% | 19% |
| Allergic-type reaction | 3% | 13% |
| Irregular heartbeat | 3% | 11% |
| Stopped because of side effects | 0% | 16% |
Most of it was mild to moderate and settled down over time. The irregular heartbeats were mild or moderate too, apart from one serious case in a person who was also taking an anti-nausea drug. Still, at the top dose about one in six people stopped because of side effects. In the later unpublished results that figure reached 18%.
One thing you will not hear elsewhere: people also reported tingling, burning or unusual skin sensitivity. In the published 48-week study it hit 13% at the top dose, against 1% on placebo. New England Journal of Medicine, 2023 The unpublished later results put it as high as 21%. It does not show up this way with semaglutide or tirzepatide, and no one has published an explanation for it.
What is still unknown
Retatrutide is not an approved medicine anywhere. Lilly plans to ask the FDA for approval in early 2027, so there is no official label yet, and these gaps are still open:
- Nothing published past 48 weeks. The two-year number is a press release.
- The heart outcomes study is not finished.
- Nothing published on pregnancy, teenagers, or type 1 diabetes.
- Nothing published on what happens after you stop.
What is in the bottle is not what was studied
One more thing.
Every retatrutide result on this page came from Lilly's own drug. Made in a pharmaceutical plant. Given under a doctor's care. Checked at every step.
No study has ever shown that a product sold online as "retatrutide" is the same thing. Not the same purity. Not the same strength. Not even proof it is the same molecule. Researchers in Australia have started testing what is actually in these bottles. Source
Here is what that can cost. Doctors published the case of a man with type 1 diabetes who bought a product sold as retatrutide online and injected it. He ended up in hospital with dangerous acid levels in his blood and kidney damage. He also had a stomach infection at the time, so the doctors could not prove the peptide caused it — because nobody knew what was in the vial. Cureus, 2026
There is one legal way to get the real thing. Lilly runs a registered early-access program, and a doctor can apply to it for a patient. It is open now. Whether anyone is accepted is up to the program, not up to us. Trial record · BMJ, 2026
So take every number on this page for what it is. It describes Lilly's drug. It describes nothing else.
How to check a number yourself
You are going to see more numbers about this drug. In a reel. In a comment. On somebody's store page.
Here is how to tell a real one from a marketing one. Five questions. About ten seconds each.
1. Is there a link to a study?
A real number comes from a paper you can open. No link means it is a claim, not a result. Search the drug name on pubmed.gov yourself. If nothing comes back, nothing was published.
There is a softer version of this trick. A published study went through a journal and outside reviewers. An announcement went through a communications team. Both can be true. Only one has been checked.
2. How big was it, and how long did it run?
Small studies swing. The best published retatrutide study had 338 people and ran 48 weeks. The Zepbound study had 2,539 people and ran 72. Same kind of headline. Very different weight behind it.
And a number is only true for as long as the study ran. Anyone quoting a two-year figure is quoting a press release.
3. Was there a group that got nothing?
The fake shot is the whole point. People lose weight just from being watched — the fake-shot group here lost 2.1%. Without that group, nobody can tell how much of the number was the drug.
4. How many people quit?
Every headline leads with weight lost. The number that tells you how the drug felt to take is further down: how many people stopped because of side effects. On this page it is 16% at the top dose, against 0% on placebo. Look for that line every time. It is almost never in the headline.
5. Who paid for it?
Almost every trial of a new drug is paid for by the company that sells it. That is normal. It matters more when that company is the only one who has seen the data.
Now run those five on this page
Every number above links to the paper it came from. The study sizes are in the table. So are the lengths. The fake-shot row is in the chart. The quit rate is in the side-effect table. And you were told more than once which figures are press releases and not studies.
The famous ones — 28%, 30% — have no link, because there is no paper to link to. Those trials are finished. The papers are not out.
That is the whole difference: a number you can check, and a number you are asked to believe.
This page has a date on it, near the top. When those papers publish, this page changes.
Read the studies yourself
- Phase 2 obesity trial, NEJM 2023 — the main one
- Phase 3 diabetes trial, Lancet 2026 — the only published late-stage study
- Phase 1b, Lancet 2022 — where the six-day number comes from
- Liver fat study, Nature Medicine 2024 — free to read
- Official trial record
The amounts above describe what a clinical trial gave to enrolled patients under a doctor's care. This is not advice, a plan, or instructions. Retatrutide is not an approved medicine. Research compounds are not for human or animal use.