Semaglutide improves BMI category in children aged 6 to 11 years in phase 3 trial

Novo Nordisk reported that once-weekly subcutaneous semaglutide, added to lifestyle modification, reduced body mass index (BMI) more than placebo among children aged 6 to younger than 12 years with obesity in the phase 3 STEP Young trial. At 68 weeks, 40.4% of semaglutide-treated participants were below the obesity threshold, compared with 0% receiving placebo.¹

“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 Ania M. Jastreboff, MD, PhD, professor of medicine and pediatrics at Yale and director of the Yale Obesity Research Center.

STEP Young was a randomized, double-blind, placebo-controlled, multinational trial involving 165 children with obesity. More than 85% had class II or III obesity at baseline. Participants received semaglutide at a maximum weekly dose of 1.7 mg or 2.4 mg, determined by baseline weight, or placebo. Both groups also received a reduced-calorie diet and increased physical activity.¹

The primary end point was percentage change in BMI from baseline to week 68. Novo Nordisk stated that the trial met this end point, but the topline announcement did not provide the mean BMI changes, between-group treatment difference, confidence intervals, or statistical analysis.

Improvement in BMI classification was a confirmatory secondary end point. The reported 40.4% result was based on the trial product estimand, which estimates the treatment effect if all participants adhered to assigned therapy. Obesity was defined using age- and sex-specific CDC growth charts as BMI at or above the 95th percentile.¹ Additional assessments include anthropometric measures, cardiovascular risk factors, glucose metabolism, and body composition, with follow-up extending to week 104.

Novo Nordisk reported that overall safety and tolerability were consistent with previous pediatric and adult studies of semaglutide and liraglutide, with no new safety concerns involving growth or pubertal development. However, the announcement did not disclose adverse-event frequencies, discontinuations, serious adverse events, or gastrointestinal event rates. These data will be important when assessing benefit-risk balance in younger children.

Semaglutide is a glucagon-like peptide-1 receptor agonist that mimics endogenous GLP-1 activity involved in glucose regulation and body weight. The STEP Young study was conducted as part of postmarketing requirements following phase 3 development of semaglutide 2.4 mg in adults and adolescents.¹ The announcement did not report a new regulatory authorization for children younger than 12 years.

Childhood obesity frequently persists into adulthood and is associated with cardiometabolic, psychosocial, and quality-of-life consequences.²⁻⁴ Current pediatric guidance emphasizes intensive, family-centered health behavior and lifestyle treatment, with pharmacotherapy considered as an adjunct for selected patients rather than a replacement for behavioral care.² Treatment options supported by randomized evidence remain comparatively limited for children in the STEP Young age range.

The findings suggest clinically meaningful movement across BMI categories in a population largely affected by severe obesity. Nevertheless, interpretation remains constrained by the small sample, reliance on company-reported topline findings, absence of numerical primary end point data, and limited information about safety and treatment discontinuation. Durability after treatment cessation and longer-term effects on growth, puberty, metabolic outcomes, and psychosocial health also remain unanswered. Full results are scheduled for presentation at ObesityWeek 2026.

References

1. Novo Nordisk. STEP Young phase 3 data: 40.4% of children living with obesity achieved a BMI below the obesity threshold with semaglutide and lifestyle modification. Published September 7, 2026. https://www.globenewswire.com/news-release/2026/09/07/3357042/0/en/novo-nordisk-step-young-phase-3-data-40-4-of-children-living-with-obesity-achieved-a-bmi-below-the-obesity-threshold-with-semaglutide-and-lifestyle-modification.html

2. Hampl SE, Hassink SG, Skinner AC, et al. Clinical practice guideline for the evaluation and treatment of children and adolescents with obesity. Pediatrics. 2023;151.

3. Kumar S, Kelly AS. Review of childhood obesity: from epidemiology, etiology, and comorbidities to clinical assessment and treatment. Mayo Clin Proc. 2017;92:251-265.

4. Schwimmer JB, Burwinkle TM, Varni JW. Health-related quality of life of severely obese children and adolescents. JAMA. 2003;289:1813-1819.