Ozempic and Wegovy changed how doctors talk about obesity treatment. Now, an experimental drug called retatrutide — nicknamed the “Godzilla” of weight-loss drugs by some doctors and patients online for the scale of its effects — is showing results in clinical trials that go well beyond weight loss alone, including real improvements in fatty liver disease and knee osteoarthritis pain. It isn’t approved for use yet, but the trial data released so far explains why it’s generating so much attention.
Key Takeaways
- In an 80-week Phase 3 trial of nearly 2,340 adults with obesity, the highest dose of retatrutide produced an average weight loss of 28.3%, compared to 2.2% on placebo — and extended data through 104 weeks showed up to 30.3% loss.
- A separate Phase 3 trial in adults with knee osteoarthritis and obesity found retatrutide reduced knee pain scores by about 74-76%, versus 40% with placebo, and left roughly 1 in 7 patients completely pain-free at 68 weeks.
- Retatrutide works by activating three hormone receptors at once (GLP-1, GIP, and glucagon) rather than the one or two targeted by earlier drugs like semaglutide (Ozempic/Wegovy) or tirzepatide (Mounjaro/Zepbound) — which researchers believe is why its effects are larger.
- Side effects are common and follow the same pattern as other drugs in this class: nausea, diarrhea, and constipation affected roughly a quarter to over 40% of participants depending on dose, and 4-11% of people discontinued the drug due to side effects.
- Retatrutide has not been approved by any regulatory agency. It’s legally available only through Eli Lilly’s clinical trials — anything sold outside that channel is unverified and potentially unsafe.
What the weight-loss trial actually found
The trial, known as TRIUMPH-1, randomized 2,339 adults with obesity or overweight (without diabetes) to one of three retatrutide doses or a placebo. After 80 weeks, participants on the highest 12 mg dose lost an average of 70.3 pounds (28.3% of body weight), compared to just 5.5 pounds (2.2%) on placebo. A smaller group of participants with higher starting BMI continued treatment to 104 weeks and reached an average loss of 85 pounds, or 30.3% of body weight — among the largest average weight-loss figures reported in a Phase 3 obesity drug trial to date.
Why it may work better than earlier drugs
Semaglutide (the active ingredient in Ozempic and Wegovy) targets one hormone receptor, GLP-1. Tirzepatide (Mounjaro and Zepbound) targets two, GLP-1 and GIP. Retatrutide adds a third: it also activates glucagon receptors, which play a role in fat burning and energy use. As one researcher put it, the point isn’t simply a stronger version of the same drug — it’s that multiple mechanisms are working together rather than one mechanism being pushed harder.
The osteoarthritis findings
A separate Phase 3 trial, TRIUMPH-4, tested retatrutide specifically in 445 adults with both obesity and knee osteoarthritis. Using a standard pain-scoring tool, the 9 mg and 12 mg doses reduced knee pain scores by about 74-76% over 68 weeks, compared to roughly 40% with placebo. In a follow-up analysis, 12-14% of patients on retatrutide were completely free of knee pain by the end of the trial, compared to about 4% on placebo. Researchers believe this reflects the direct effect of significant weight loss on joint load, rather than a separate action on the joint itself — but the size of the effect is notable regardless of mechanism.
Separately, in a smaller trial focused on fatty liver disease, 86% of participants on the highest dose reached normal liver fat levels after about five and a half months — a result researchers link to glucagon’s role in reducing fat stored in the liver specifically.
The side effects are real and worth knowing
Across the trials, the most common side effects were gastrointestinal: nausea affected roughly 29-43% of participants depending on dose and trial, with diarrhea, constipation, and vomiting also common. A skin-related side effect called dysesthesia (an altered, sometimes unpleasant sensation) occurred in up to about 21% of treated patients in the osteoarthritis trial, compared to under 1% on placebo. Discontinuation due to side effects ranged from about 4% at the lowest dose to over 11% at the highest dose in the weight-loss trial — meaningfully higher than the roughly 5% seen with placebo.
What’s not known yet
Retatrutide remains investigational — it has not been approved by the FDA or any other regulatory agency, and it’s only legally available through Eli Lilly’s clinical trials. Longer-term safety data beyond about two years isn’t yet available, and researchers are candid that the full risk profile of a drug with this many combined effects isn’t completely understood yet. There’s also a real safety concern around unverified versions of the drug being sold outside of legitimate trials or pharmacies — those products carry unknown risks since they aren’t manufactured or tested to any confirmed standard.
Sources: Eli Lilly and Company, TRIUMPH-1 Phase 3 trial results; Eli Lilly and Company, TRIUMPH-4 Phase 3 trial results on osteoarthritis; BBC Science Focus, “The most powerful weight-loss drug ever tested has arrived”.
This article is for informational purposes and isn’t a substitute for medical advice. Retatrutide is not currently approved for use outside of clinical trials; talk to your doctor about approved weight-loss treatment options.