Tirzepatide produced large weight loss in Japanese adults with obesity in a phase 3 trial
New phase 3 results show how much weight Japanese adults lost on tirzepatide over 72 weeks, adding data from a population where evidence had been limited.
Japanese adults with obesity disease who received tirzepatide lost far more weight than those who received a placebo over 72 weeks, according to a phase 3 trial published in The Lancet Diabetes & Endocrinology. The estimated treatment difference relative to placebo in body weight change at week 72 was -16.1% at the 10 mg dose and -21.1% at the 15 mg dose, both with p values below 0.0001 [1].
The trial tested tirzepatide, the molecule sold in the United States as Mounjaro and Zepbound [1].
Who was in the trial
The study, called SURMOUNT-J, screened 413 people and randomly assigned 267 between May 10, 2021, and June 24, 2023 [1]. After one study site was excluded, the main analysis covered 225 participants: 133 men (59%) and 92 women (41%), with a mean age of 50.8 years (SD 10.7). They were divided into three groups - 73 on tirzepatide 10 mg, 77 on tirzepatide 15 mg and 75 on placebo - and 192 people (85%) completed both the study and its treatment [1]. The drug was given as a once-weekly injection under the skin alongside lifestyle changes [1].
Participants had "obesity disease" as the Japanese Society for the Study of Obesity defines it: a BMI of at least 25 kg/m2 with excessive fat accumulation [1]. To enter the trial, however, people needed a BMI of at least 27 kg/m2 plus two or more obesity-related health disorders, or a BMI of at least 35 kg/m2 plus at least one such disorder. People with diabetes were excluded [1].
The two main measures were the mean percent change in body weight and the share of participants who lost at least 5% of body weight at week 72 [1]. On the second measure, 67 of 71 people (94%) on 10 mg and 73 of 76 (96%) on 15 mg lost at least 5%, compared with 15 of 75 (20%) on placebo. Both comparisons were statistically significant, with p values below 0.0001 [1]. Cardiometabolic and body composition measures also improved with tirzepatide, the authors reported [1].
Side effects and funding
Treatment-emergent adverse events were reported more often with tirzepatide - 61 people (84%) on 10 mg and 66 (86%) on 15 mg - than with placebo, at 52 people (69%). Gastrointestinal symptoms were the most common [1]. Discontinuations because of adverse events were infrequent: 3 (4%) on placebo, 1 (1%) on 10 mg and none on 15 mg [1].
The authors concluded that in Japanese adults with obesity disease, tirzepatide "provided clinically a meaningful reduction in bodyweight compared with placebo over 72 weeks, with a safety profile consistent with that observed in global populations" [1]. The trial was funded by Eli Lilly and Company, and the published conflict-of-interest statement lists authors with consulting fees, lecture honoraria or employment at Lilly and other drugmakers [1].
Why it matters for patients
The trial addresses a group in which tirzepatide data had been limited. Its background section notes that data on the drug in Asian patients with obesity are sparse [1], so these results add evidence that the weight-loss effect seen in global trials also appears in Japanese participants, with a similar safety pattern [1].
How obesity is defined matters for who gets treated. Japan uses a lower BMI cutoff than the United States does, and SURMOUNT-J used its own entry thresholds on top of that [1]. Someone comparing these results with US trial data should note that the participants were selected by different criteria and that everyone in the study also received lifestyle modification [1].
The findings do not describe tirzepatide's weight effects in people with type 2 diabetes, since diabetes was an exclusion [1]. They also reflect an efficacy analysis, which estimates the treatment effect among participants rather than counting everyone who dropped out, and 15% of participants did not complete the study and treatment [1].
Several things remain unstated. Whether these results will lead to new regulatory submissions, approvals or label changes in Japan or elsewhere has not been reported [1]. Weight change after stopping the drug, and outcomes beyond 72 weeks, are not covered in this report [1].
What happens next
No next milestone has been disclosed. The trial is registered with ClinicalTrials.gov as NCT04844918 [1], and results were published with an accompanying commentary in The Lancet Diabetes & Endocrinology [1].
Sources
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