What Is GLP-3 RT? Why "GLP-3" Is a Label for Unapproved Retatrutide

Written by Olha Orlyk. Updated October 24, 2026.

"GLP-3" is not a hormone, a drug class, or an approved medicine. It is a nickname that peptide sellers and social media use for retatrutide, Eli Lilly's experimental triple-hormone weight-loss drug, and "GLP-3 RT" is simply the product name those sellers put on vials of unapproved retatrutide sold "for research use only." The real drug exists and has produced the largest weight loss ever seen in a trial, about 29% at 68 weeks, but as of October 2026 it is not approved anywhere, and the only legal way to take it is inside a clinical trial.

This guide explains where the "GLP-3" name came from, what retatrutide actually is, why the vials sold online are a different thing from the drug in Lilly's trials, what FDA has done about them, and what to watch for as the real product moves toward approval.

Weight-loss drugs are usually described by the gut hormones they imitate. Ozempic and Wegovy copy one hormone, GLP-1. Zepbound and Mounjaro copy two, GLP-1 and GIP; some people loosely call tirzepatide a "GLP-2," which is also wrong, because GLP-2 is a real and unrelated gut hormone. Retatrutide copies three: GLP-1, GIP and glucagon. By the same loose logic, it became "GLP-3" on TikTok, Reddit and vendor sites. Scientists call it a triple agonist, or "triple G."

The name stuck because it is catchy and sounds like a natural upgrade: GLP-1, GLP-2, GLP-3. It is also useful to sellers, because searching "GLP-3" leads to their product pages rather than to Lilly's trial results or FDA's warnings. If you have seen "GLP-3 RT," "RT3" or "Reta" on a vial, you are looking at retatrutide marketed around the regulatory system, not a new molecule.

Retatrutide is a single peptide, developed by Eli Lilly, that activates three receptors at once: GLP-1 (which lowers appetite and slows digestion), GIP (which adds appetite suppression and improves how fat is handled) and glucagon (which raises energy expenditure and helps the liver burn fat). It is given as a once-weekly injection in the trials. Our what is retatrutide guide covers the biology in depth.

The glucagon piece is what makes it different from everything on the market. Glucagon on its own raises blood sugar, which is why earlier glucagon-based drugs failed; combining it with GLP-1 and GIP balances that out while keeping the extra calorie burn. The result in trials has been weight loss beyond what tirzepatide achieves, with a trade-off in side effects that is still being worked out.

In TRIUMPH-4, nearly a quarter of people on the 12 mg dose lost 35% or more of their body weight, and knee pain fell by about three-quarters. The flip side: about 18% of people on 12 mg stopped because of side effects, versus 4% on placebo, mostly nausea, vomiting and diarrhea. That is a higher dropout rate than tirzepatide's trials showed, and it is why Lilly is testing slower dose increases. We track every readout in approval watch and compare the numbers with Zepbound in retatrutide vs tirzepatide.

No. As of October 2026, retatrutide is not approved by FDA or any other regulator. The three main obesity trials (TRIUMPH-1, 2 and 3) reported in May and July 2026, and Lilly has said it will submit a Biologics License Application in the first quarter of 2027 once manufacturing data are complete; a standard review would put a decision in late 2027 or 2028. Until then there is no pharmacy, no prescription and no legal retail product. Any website selling "retatrutide" or "GLP-3 RT" to the public is selling an unapproved drug.

FDA has issued warning letters to companies selling retatrutide and other peptides, including a March 2026 letter to a California seller that marketed retatrutide as "GLP-1-R Peptide" and tirzepatide as "GLP-2 Peptide" with research-use disclaimers. FDA's position in those letters is that the products are unapproved new drugs and that the disclaimer does not change their intended use when the website describes effects on appetite and fat loss. Public Citizen's June 2026 report counted 14 FDA warning letters to retatrutide sellers since 2024, found that 11 of those companies were still advertising peptides as of May 2026, and reported 14 hospitalizations linked to retatrutide in FDA's adverse event database.

The pattern is the same one seen with compounded and gray-market semaglutide and tirzepatide: enforcement is slow, sellers rebrand, and influencers with large followings act as affiliates. The difference with retatrutide is that there is no approved version at all to fall back on, so every vial in circulation is unverified.

Our side effects page lists what the trials have reported. None of it has been studied in self-injected vendor product.

If you want the real drug rather than a vial with a made-up name, the only route today is a clinical trial. We explain how to find one, what you risk, and what to use until approval in how to get retatrutide legally.

"GLP-3 RT" is a marketing name for unapproved retatrutide, not a new hormone or an upgrade you can buy. The real drug is remarkable in trials, with weight loss near 29% at 68 weeks, and it may well be approved in 2027. The vials sold online today are not that drug in any verifiable sense, FDA has said selling them is illegal, and people have been hospitalized. If you want retatrutide, the honest routes are a clinical trial now or a prescription later. For what the trial data actually show, start with what is retatrutide and the big weight loss headline.

This article is for information only and is not medical advice. Retatrutide is not approved for any use; do not buy or inject unapproved products.