Tirzepatide produced 13.6% and 17.5% weight loss in Chinese obesity trial

In a 52-week phase 3 trial in China, adults with obesity or overweight who took once-weekly tirzepatide injections lost an average of 13.6% of their body weight on the 10 mg dose and 17.5% on the 15 mg dose, compared with 2.3% for those who received placebo, according to results published in JAMA ^[1]. Everyone in the trial also received a lifestyle intervention ^[1].

Tirzepatide is the active ingredient in Mounjaro, which is used for type 2 diabetes, and Zepbound, which is used for weight loss in the United States.

The trial, called SURMOUNT-CN, ran at 29 centers in China from September 2021 to December 2022 and enrolled 210 adults ^[1]. Participants were 18 or older and had a body mass index of at least 28, or at least 24 along with at least one weight-related health condition ^[1]. People with diabetes were excluded ^[1]. Participants were assigned in equal groups to 10 mg tirzepatide (70 people), 15 mg tirzepatide (71 people) or placebo (69 people) ^[1].

At the start, participants averaged 36.1 years of age, 49.0% were female, average body weight was 91.8 kg and average BMI was 32.3 ^[1]. Nearly all of them — 201 of 210, or 95.7% — completed the 52 weeks ^[1].

The average body weight change at week 52 was -13.6% (95% CI, -15.8% to -11.4%) with 10 mg tirzepatide, -17.5% (95% CI, -19.7% to -15.3%) with 15 mg and -2.3% with placebo ^[1]. The difference from placebo was -11.3 percentage points for the 10 mg dose and -15.1 percentage points for the 15 mg dose, both with P values below .001 ^[1].

The share of participants who lost at least 5% of their body weight was 87.7% on 10 mg tirzepatide, 85.8% on 15 mg and 29.3% on placebo ^[1].

The most frequent treatment-emergent side effects with tirzepatide were gastrointestinal ^[1]. Most were mild to moderate, and few events led to treatment discontinuation, a rate the authors put at under 5% ^[1]. The authors concluded that tirzepatide produced statistically significant and clinically meaningful weight reduction with an acceptable safety profile in this population ^[1].

Two of the authors reported being employees and shareholders of Eli Lilly and Company during the study; no other disclosures were reported ^[1]. A correction notice for the trial report, titled "Errors in Figure, Results, and End Matter," was published in JAMA on August 20, 2024 ^[1]. The notice itself does not spell out what was corrected ^[1]. JAMA also published two companion opinion pieces, one titled "Tirzepatide—New Evidence for the Treatment of Obesity From China" and another on the implications for the global obesity epidemic ^[1].

Why it matters for patients

The results give a concrete sense of what a year on tirzepatide produced in a controlled trial: roughly one in seven body weight lost at the lower dose studied, and closer to one in six at the higher dose, with placebo participants on a lifestyle program losing about 2% ^[1]. Trial averages are not predictions for any one person, and the trial did not test the lower starter doses that US patients typically begin with, only 10 mg and 15 mg ^[1].

Because the trial enrolled only Chinese adults and excluded people with diabetes, whether the same results would appear in other groups has not been established from this study ^[1]. The report covers 52 weeks of treatment; what happened after treatment ended, and whether weight was maintained, has not been reported from this trial ^[1].

What happens next

No dated milestones for this trial have been disclosed. The study is registered as NCT05024032 ^[1]. Whether the findings lead to regulatory action in China, to changes in US product labeling, or to further trials has not been announced ^[1].