Retatrutide: The Triple Agonist and What the TRIUMPH Trials Show

Retatrutide is an investigational weekly injection that works on three gut and metabolic hormone pathways at once, which is why scientists call it a triple agonist. Most current drugs are simpler. Semaglutide (Ozempic, Wegovy) copies one hormone, GLP-1, which slows digestion and calms appetite. Tirzepatide (Mounjaro, Zepbound) copies two, GLP-1 and GIP. Retatrutide copies those two and adds a third, glucagon.

That third target is the interesting part. Glucagon can raise the body's energy burn and help the liver release stored fat. Pairing it with GLP-1 and GIP appears to combine strong appetite control with a modest bump in metabolism. The result in trials has been larger weight loss than researchers had seen before.

Retatrutide was developed by Eli Lilly, the same company behind tirzepatide. As of 2026 it is still being studied and is not yet approved by the U.S. Food and Drug Administration (FDA). That means it is not available by prescription outside of clinical trials. If you are weighing your current options, our guide to [tirzepatide vs semaglutide](/blog/tirzepatide-vs-semaglutide-which-works-better-2026) covers the two approved medications people ask about most.

In the Phase 3 TRIUMPH-1 trial, adults with obesity lost an average of 28.3% of their body weight at 80 weeks, rising to as much as 30.3% at 104 weeks on the 12 mg dose, while the placebo group lost only 3.9% (TRIUMPH-1, 2026). Lower doses still worked well: about 17.6% at 4 mg, 23.7% at 9 mg, and 25.0% at 12 mg at the 80-week mark.

An earlier Phase 3 readout, TRIUMPH-4, reported a 28.7% reduction at 68 weeks on the 12 mg dose (TRIUMPH-4, 2025). To put that in context, tirzepatide's landmark SURMOUNT-1 trial produced about 20.9% at the top dose, and semaglutide's STEP 1 trial produced about 14.9%. Retatrutide's numbers are the highest yet reported in a randomized Phase 3 trial for this drug class.

These figures describe averages, not guarantees. Individual results vary with dose, diet, activity, and how long someone stays on treatment. Weight loss also tends to slow over time, which is normal and something we explain in our guide to [weight loss plateaus](/blog/glp1-weight-loss-plateau-why-stalls-happen-and-how-to-break-them).

Weight was not the only thing that changed. In TRIUMPH-4, participants reported a 75.8% reduction in osteoarthritis knee pain, an LDL ("bad") cholesterol drop of roughly 20%, and a 72% reversal rate of prediabetes back to normal blood sugar (TRIUMPH-4, 2025). Because glucagon also acts on the liver, researchers are studying whether retatrutide can reduce liver fat in people with fatty liver disease.

These secondary findings matter because obesity rarely travels alone. It often comes bundled with joint pain, high cholesterol, and rising blood sugar. A single medication that nudges several of those at once could simplify care, though longer trials are needed to confirm the benefits hold and are safe over years, not just months.

Seven additional TRIUMPH trials are scheduled to report in 2026, including TRIUMPH-2 (obesity with type 2 diabetes) and TRIUMPH-3 (obesity with established cardiovascular disease). A separate diabetes trial, TRANSCEND-T2D-1, published in March 2026, showed about 16.8% weight loss at 40 weeks in people with type 2 diabetes on the 12 mg dose.

The side effects reported so far look similar to other GLP-1 medications, and most are digestive. The most common are nausea, diarrhea, constipation, and vomiting, especially when the dose is being increased. In trials these were usually mild to moderate and tended to ease as people's bodies adjusted over several weeks.

Because retatrutide adds glucagon activity, researchers watched closely for changes in heart rate and blood sugar. Small increases in heart rate have been seen with the whole drug class, and this is one reason the medication is still being studied carefully. As with other GLP-1 drugs, slow dose increases (called titration) help reduce stomach upset.

Many side effects overlap with what people already experience on approved medications, so the strategies are similar: eat smaller protein-forward meals, stay hydrated, and go slow. If you are on a current GLP-1 and struggling, our articles on [managing GLP-1 constipation](/blog/glp1-constipation-why-it-happens-and-how-to-fix-it) and [GLP-1 fatigue](/blog/glp1-fatigue-why-youre-tired-and-how-to-boost-energy) offer practical, everyday tips that will likely apply to newer drugs too.

There is no confirmed launch date. Retatrutide is still moving through Phase 3 testing, the final research stage before a company can ask the FDA for approval. With strong TRIUMPH-1 and TRIUMPH-4 results in hand and more trials reporting through 2026, Eli Lilly is expected to file for approval, but the FDA review process itself takes time.

Even after approval, real-world access depends on manufacturing capacity, insurance coverage, and pricing, the same hurdles that have shaped availability of current drugs. Compounded versions are not a shortcut here; retatrutide is investigational, so any product claiming to be retatrutide sold outside a clinical trial should be treated with strong caution.

If you are curious whether a pill might come first, the landscape is shifting quickly. Our explainer on [orforglipron, the first oral GLP-1](/blog/orforglipron-first-oral-glp1-pill-explained) covers a different approach that could reach pharmacies on its own timeline. The bigger picture: the next few years will bring more options, not fewer.

On the trial numbers alone, retatrutide's weight-loss results are higher than both Zepbound (tirzepatide) and Wegovy (semaglutide), but there is an important catch: those other drugs are approved and available now, while retatrutide is not. Trial averages also come from carefully selected participants and cannot be directly compared across studies without caution.

Here is a simple way to think about it. Semaglutide targets one hormone, tirzepatide targets two, and retatrutide targets three. In general, adding targets has produced larger average weight loss in trials, but it may also mean more to learn about long-term safety. Approval and time in the real world are what turn promising trial data into a trusted everyday option.

For now, the practical choice for most people is between medications already on the market. Our comparisons of [Wegovy vs Zepbound](/blog/wegovy-vs-zepbound-which-wins-for-weight-loss-2026) walk through effectiveness, cost, and side effects for the options you can actually get today.