Semaglutide Phase 3 Trial: 40% of Children With Obesity Achieve Non-Obese BMI

In a Phase 3 clinical trial, 40.4% of children aged 6 to 11 who received weekly semaglutide injections alongside lifestyle changes were no longer classified as clinically obese after 68 weeks. The STEP Young trial results, announced by Novo Nordisk on September 7, 2026, demonstrated that the GLP-1 receptor agonist successfully reduced body mass index (BMI) below the obesity threshold for two out of five treated children, compared to zero percent in the placebo group.[1][2][3][4]

The multinational trial enrolled 165 children, the vast majority of whom entered the study with severe weight conditions. More than 85% of the participants began the trial with class II or class III severe obesity, which corresponds to an adult BMI of 35 or 40.

"Most of the children in the STEP Young trial were classified as having severe (class II or III) obesity at baseline, yet treatment with semaglutide resulted in a BMI percentile category below the obesity threshold in approximately 40% of the children within about a year of treatment," said Dr. Ania M. Jastreboff, Director of the Yale Obesity Research Center.[2][3]

Throughout the 68-week study, all participants received standard lifestyle modification support, including a reduced-calorie diet and increased physical activity. Children in the active treatment arm received a maximum once-weekly subcutaneous dose of either 1.7 milligrams or 2.4 milligrams of semaglutide, calibrated to their starting body weight. The placebo group, which received the exact same dietary and exercise interventions, saw none of its participants drop below the obesity threshold.[1][2][4][5]

Treating young children with GLP-1 medications has historically raised questions about potential impacts on physical maturation. However, Novo Nordisk reported that the safety and tolerability profile matched previous trials in adults and older adolescents. Crucially, investigators identified no new safety concerns related to growth or pubertal development during the 68-week period.[2][3]

"We are encouraged by the positive STEP Young results and semaglutide's potential to help children living with obesity who need medical treatment, alongside lifestyle changes, to better manage their obesity," said Martin Holst Lange, Novo Nordisk's chief scientific officer. The company plans to present the detailed dataset at the ObesityWeek conference in Washington, D.C., in November 2026. The results mark a significant expansion of the target demographic for semaglutide, which is already prescribed widely for adults and older teens.[1][3][5]

Despite the clinical success, Novo Nordisk's stock dipped nearly 2% following the announcement, as the positive pediatric data arrived alongside news of two unrelated trial cancellations in the company's broader pipeline. The clinical validation arrives as clinicians increasingly look for effective interventions for severe pediatric obesity, a condition that has historically proven highly resistant to diet and exercise alone.[1][5][6]

Childhood obesity strongly predicts adult obesity, bringing early onset of cardiovascular disease, type 2 diabetes, and shortened life expectancy. By demonstrating that pharmacological intervention can effectively reverse severe obesity classification before adolescence, the STEP Young trial provides a new evidence base for treating pediatric obesity aggressively. For parents and pediatricians, these findings suggest that medical intervention may soon be a viable option when lifestyle changes alone prove insufficient.[2][3][5]

The data will now form the basis of regulatory submissions as Novo Nordisk seeks to expand semaglutide's label to include children as young as six. Until those approvals are granted, the medication remains officially off-label for this youngest cohort, leaving clinicians to weigh the striking 68-week efficacy against the long-term realities of initiating chronic weight-management therapy in elementary-school-aged patients.[1][4][5]