Retatrutide: The ‘GLP-3’ Weight-Loss Drug That Beats Ozempic — and Why to Be Careful

The experimental “GLP-3” helped trial participants lose around 28% of their body weight — but the versions currently sold online are unapproved and potentially dangerous.

The success of GLP-1 weight-loss drugs such as Ozempic and Wegovy has sparked a pharmaceutical gold rush, with companies racing to develop medications that produce even greater weight loss. One of the most closely watched is Eli Lilly’s retatrutide, an experimental injection sometimes nicknamed the “GLP-3.”

Its results have been striking, approaching the weight loss sometimes seen after bariatric surgery. But retatrutide is still being studied and has not been approved by the Food and Drug Administration (FDA). That hasn’t stopped unregulated sellers from marketing supposed versions of “reta” online — products whose ingredients, potency, and purity cannot be reliably verified. Here’s what the research shows and why taking the drug outside a legitimate clinical trial is such a risk.

What You Should Know About Retatrutide

To understand how retatrutide works, it helps to start with familiar GLP-1 medications. Semaglutide — the active ingredient in Ozempic and Wegovy — activates receptors for glucagon-like peptide-1 (GLP-1), a gut hormone that reduces appetite and promotes fullness by slowing the rate at which food leaves the stomach. It also helps regulate blood sugar by stimulating insulin release when glucose levels are elevated and limiting glucagon release, a hormone that raises blood sugar.

Tirzepatide, sold as Zepbound for weight management, activates GLP-1 receptors along with receptors for glucose-dependent insulinotropic polypeptide, or GIP, another hormone involved in appetite and blood-sugar regulation.

Retatrutide goes one step further, as it’s a triple agonist. That is, a drug that activates three types of receptors — targeting GLP-1, GIP, and glucagon receptors. The first two primarily help people eat less, while glucagon-receptor activity may also increase energy expenditure. In other words, retatrutide may reduce the calories coming in while helping the body use more energy. That three-pronged action explains its informal “GLP-3” nickname, though GLP-3 is not an actual hormone or medical drug class.

In Eli Lilly’s December 2025 TRIUMPH-4 Phase 3 trial, participants receiving the highest dose lost an average of 28.7% of their body weight over 68 weeks. That approaches the roughly 30% weight loss associated with some forms of bariatric surgery and exceeds the average results reported in major trials of semaglutide and tirzepatide — though the drugs have not yet been compared in a head-to-head trial.

Going Deeper on the Black-Market Problem

Retatrutide is not FDA-approved and is not legally available outside clinical trials. That means any vial sold online as compounded, “research-grade,” or black-market “reta” is an unapproved product whose identity, concentration, purity, and sterility cannot be reliably verified. Because these products sit entirely outside regulatory oversight, there’s no guarantee of what’s actually in the vial — unknown ingredients, contaminants, or impurities are all possible.

“There are, like, seven active Phase 3 trials with results expected in 2026 and 2027,” Kevin Gendreau, MD, an obesity physician at Signature Healthcare in Brockton, Massachusetts, told Super Age. “So the dosing is really unsure, and the purity of these compounds is also in question because there’s no batch testing of the drug.”

The risks go beyond receiving a contaminated or incorrectly dosed injection. Retatrutide is powerful enough to produce substantial changes in weight, blood pressure, blood sugar, and cholesterol, which may cause dangerous interactions with medications a person is potentially taking. Losing weight rapidly can also mean losing muscle and potentially bone, particularly without sufficient protein, strength training, and clinical monitoring.

The drug itself can cause side effects, too. In Lilly’s Phase 3 trials, the most common were nausea, diarrhea, constipation, and vomiting; some participants also experienced altered or unpleasant skin sensations. The drug also nudges heart rate up slightly, though trials haven’t tied that to adverse cardiovascular events. Online users have reported other symptoms, including sulfur-tasting burps and emotional blunting, but those reports do not prove that retatrutide caused them.

If retatrutide is eventually approved, it may become an important medical option for people with obesity. The danger is taking an unfinished treatment without a verified product, a regulated dose, or a clinician managing the risks.

The Takeaway

Retatrutide’s weight-loss results are admittedly striking, but an unapproved injectable bought online is a gamble with your health. Anyone considering a GLP-1-class medication should work with a qualified clinician who can oversee dosing, manage side effects, and help preserve muscle through adequate protein and strength training.

Bottom Line

Phase 3 data suggest retatrutide may produce greater average weight loss than current medications such as semaglutide and tirzepatide. What remains unclear is its full side-effect profile, long-term safety, and approval timeline as additional trials report results through 2026 and 2027. Until the drug is approved, avoid black-market or “research-use” versions and discuss regulated options with a qualified medical provider.