Retatrutide

Retatrutide (LY3437943) is an investigational once-weekly peptide that activates three receptors — GIP, GLP-1, and glucagon — and is being studied by Eli Lilly for obesity and type 2 diabetes in clinical trials. It is NOT FDA-approved and is not an available medicine. This page is educational only and is not medical advice; any decision about an investigational drug belongs with a licensed clinician.

Important: Retatrutide is a drug still going through human trials, not an approved product and not a settled supplement. Powders sold online as "research chemicals" are not the trial material and are not tested or quality-controlled for human use. WikiPeps does not sell retatrutide, does not say where to obtain it, and does not provide dosing amounts.

What is Retatrutide?#

Retatrutide is a synthetic peptide developed by Eli Lilly under the code name LY3437943. It belongs to the same broad family as semaglutide and tirzepatide but goes a step further: it is a triple agonist that engages three hormone receptors simultaneously — the GIP receptor, the GLP-1 receptor, and the glucagon (GCGR) receptor. Because of that third target, it is sometimes informally called a "GLP-3" or triple-G agonist. It has a long half-life (about 6 days) that, in trials, supports once-weekly subcutaneous dosing.

It is an investigational compound. That means it is still being tested in humans and has not been judged safe and effective by the FDA for any use.

How does Retatrutide work?#

The three receptors retatrutide activates each influence metabolism in a different way:

• GLP-1 receptor: promotes insulin release when blood sugar is high, slows gastric emptying, and increases satiety (feeling full).
• GIP receptor: another incretin pathway that works alongside GLP-1 to influence insulin response and appetite.
• Glucagon receptor: classically raises blood sugar, but sustained low-level activation in this context is thought to increase energy expenditure (calorie burn), which is the feature that distinguishes retatrutide from single- and dual-agonists.

Structural and preclinical work suggests retatrutide is tuned to be relatively more potent at GIP and somewhat less potent at the GLP-1 and glucagon receptors compared with the natural hormones. In animal studies this combination produced greater weight loss than dual agonists, but animal findings do not automatically carry over to humans.

What is Retatrutide studied for?#

Retatrutide has published phase 2 human data and ongoing phase 3 trials (Eli Lilly's TRIUMPH program), but no use is FDA-approved. The table below summarizes the main research themes.

In the phase 2 obesity trial, participants on higher doses experienced large average weight reductions over roughly a year, but this was a 338-person trial of limited duration. Phase 3 trials are designed to confirm whether these effects hold up and are safe over the long term.

Is Retatrutide legal and FDA-approved?#

No — retatrutide is not FDA-approved. It is an investigational drug, meaning it can lawfully be given to humans only within registered clinical trials under regulatory oversight. There is no approved prescription form, no approved brand, and no approved indication.

Because it is not approved, retatrutide cannot legally be sold or prescribed for human use. Vendors that offer it almost always label it "for research use only," which is not the same as being safe, legal, or appropriate to inject. Such products are not subject to the identity, purity, sterility, and potency controls that finished medicines must meet, and buying or self-administering them carries legal, quality, and health risks. WikiPeps does not link to sellers or advise on sourcing.

How is Retatrutide dosed in research?#

There is no validated human dose outside of a clinical trial, and WikiPeps does not publish dosing protocols or amounts. In trials, dosing is selected, titrated, and monitored by investigators under strict protocols; those numbers are not a do-it-yourself guide and do not transfer to unsupervised use of an unregulated powder. Any question about whether retatrutide is appropriate — and at what dose, if ever — belongs with a licensed clinician, ideally in the context of a monitored trial.

How is Retatrutide reconstituted?#

If you have encountered a lyophilized (freeze-dried) vial, reconstitution is simply the laboratory step of dissolving the powder in a sterile diluent; it is not an endorsement of human use. For a careful, general walkthrough of sterile technique and the math involved, see our guide at /learn/guides/how-to-reconstitute-a-peptide. That guide, and the educational overview in this page's structured steps, deliberately avoid human dosing amounts.

What are the safety considerations?#

The most frequently reported adverse events in retatrutide trials were gastrointestinal — nausea, vomiting, diarrhea, and constipation — which were generally mild to moderate, dose-related, and more common when starting or escalating. Trials also observed dose-dependent increases in heart rate. Because activating the glucagon receptor can influence blood sugar and other metabolic parameters, monitoring in trials is close.

Critically, long-term safety in humans is not established, and the unregulated powders sold online add further hazards: unknown purity, contamination, incorrect labeling, and non-sterile handling. Anyone considering an investigational metabolic drug should do so only under medical supervision. This page is not medical advice, and retatrutide is not proven safe or effective for any use in humans outside of controlled trials.

The bottom line#

Retatrutide (LY3437943) is a promising but investigational triple GIP/GLP-1/glucagon agonist that Eli Lilly is studying for obesity and type 2 diabetes. Early human trials reported substantial weight loss and metabolic improvements, but it is not FDA-approved, its long-term safety is unproven, and "research use only" powders are neither the trial product nor a safe substitute. There is no validated human dose, WikiPeps does not provide one, and the right next step for anyone interested is a conversation with a licensed clinician.