Mazdutide's US Phase 2 Trial: What a 179-Person Study Shows

What happened / Why it matters

What happened. Mazdutide is an experimental drug and is not FDA-approved as of Nov. 5, 2026. The only US trial of it with published results that we found is a phase 2 study, published online in The Lancet Diabetes & Endocrinology on Aug. 21, 2026 and now in the journal’s November print issue. This is not a new result. We are looking at it because the drug’s other evidence comes from China, and because “mazdutide” is being sold online. ClinicalTrials.gov lists other Eli Lilly studies of mazdutide with US sites, including phase 1 studies and a phase 2 trial in alcohol use disorder, with no results posted that we found.

Why it matters. Most of what has been reported about mazdutide comes from phase 3 trials in Chinese adults. The US trial is smaller and earlier-stage, and it is the only published evidence in a US population that we found. It is an analysis of what that one trial can and cannot tell a reader. It is not medical advice.

What did the US trial do?

According to the abstract and the registry entry:

• Design. A phase 2, double-blind, placebo-controlled trial at 24 centers in the US, lasting 48 weeks. Participants were randomly assigned to placebo or to one of three mazdutide dose groups, given as a weekly injection. The dose groups are the trial’s design, not a recommendation.
• Who. 179 adults aged 18 to 75 with obesity, or with overweight plus a weight-related condition, and no type 2 diabetes. The average age was 47.7 and 66% were women.
• Main measure. The percentage change in body weight at 32 weeks, using the efficacy estimand (a hypothetical analysis).
• Funding. Eli Lilly and Company.

What did it find?

In a 179-person phase 2 trial in the US, funded by Eli Lilly, weight fell 7.3% to 18.1% at 32 weeks across doses, compared with 0.9% on placebo. These are efficacy-estimand results, which assume people stayed on treatment.

By dose group, the average weight change at 32 weeks was −7.3% in the lowest group, −15.6% in the middle group and −18.1% in the highest group, versus −0.9% on placebo. Differences from placebo ranged from −6.5 to −17.2 percentage points. The abstract says additional weight reductions were seen at 48 weeks but gives no figures, and we do not report any.

The study was published online in August 2026.

What about side effects and dropouts?

The most common adverse events were gastrointestinal and mostly mild to moderate, according to the abstract. At the highest dose, 20% of participants stopped treatment because of side effects, mostly gastrointestinal.

That number is about stopping the study drug. The registry entry reports a different measure, people who left the study because of adverse events, and the two should not be read as the same figure. We do not compare them here.

Why is this the only published US evidence?

The phase 3 trials we found were run in China, in Chinese adults. GLORY-1 (New England Journal of Medicine) enrolled adults in China, and GLORY-2 (JAMA) did the same. Results in one population do not automatically carry over to another. The US phase 2 trial is small. According to FDA, phase 2 studies look at efficacy and side effects in more people, and phase 3 studies aim to show whether a product offers a treatment benefit. We do not compare the US numbers with the China numbers, because the trials differ in design, dose, length and people.

What has FDA said?

Mazdutide is not approved in the US: a search of FDA’s Drugs@FDA data on Nov. 5 found no product listed under that name. We did not verify any approval elsewhere.

FDA has cited “mazdutide” sold online as a research peptide as an unapproved new drug. It did so in warning letters dated March 31, 2026 and Aug. 24, 2026. In those letters, FDA said that “research” labels did not change its conclusion, because evidence on the sellers’ websites established that the products were intended for human use. Products sold online are not the product used in the trials, and FDA has not reviewed them. See our tracker of FDA warning letters on peptides and our guide to what FDA says “research use only” means.

What is still unknown?

Long-term safety, effects on heart health, and how mazdutide compares with approved drugs: we found no published head-to-head trial against another drug. Whether and when a company will seek FDA approval is not something we have found a source for. Anyone considering weight-loss treatment should talk with a licensed clinician about approved options and the evidence for each. We do not link to or recommend sellers.

U.S. status checked Nov. 5, 2026. Based on the trial’s abstract and registry entry; we did not read the full text.