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Efficacy and Safety of Once-Weekly Semaglutide in Pediatric Patients Aged 6 to 11 Years With Obesity: Topline Findings From the STEP Young Trial
Once-weekly subcutaneous semaglutide (Wegovy; Novo Nordisk) paired with lifestyle modification produced significantly greater reductions in body mass index (BMI) compared with placebo in children aged 6 to 11 years with obesity, according to topline results from the multicenter phase 3 STEP Young trial.
Trial Design and Baseline Characteristics
The STEP Young study represents the first phase 3 clinical trial to assess the safety and therapeutic efficacy of semaglutide in pediatric patients younger than 12 years. The trial evaluated 165 pediatric participants with obesity over a 68-week intervention period. Participants were randomized to receive either once-weekly semaglutide or placebo, administered alongside a reduced-calorie dietary regimen and structured physical activity. Semaglutide was titrated to a maximum weekly maintenance dose of either 1.7 mg or 2.4 mg, determined by patient body weight at trial initiation. The primary clinical end point was percentage change in BMI from baseline to week 68.
Table 1. STEP Young Trial Design and Cohort Baseline Characteristics
| Parameter | Study Specification |
| Study Phase & Name | Phase 3 randomized controlled trial; STEP Young |
| Study Population | Children aged 6 to 11 years with clinical obesity ($N = 165$) |
| Baseline Disease Severity | >85% classified with class 2 or class 3 severe obesity |
| Treatment Arms | Semaglutide subcutaneous injection vs placebo (1:1 randomization) |
| Dosing Strategy | Maximum maintenance dose of 1.7 mg or 2.4 mg weekly (weight-tiered) |
| Co-Interventions | Caloric restriction (reduced-calorie diet) and increased physical activity |
| Treatment Duration | 68 weeks |
| Primary End Point | Percentage change in BMI from baseline to 68 weeks |
Efficacy and Safety Findings
Children treated with semaglutide demonstrated a significantly greater reduction in BMI percentage at 68 weeks compared with those in the placebo cohort. At the completion of the 68-week period, 40.4% of patients in the semaglutide arm had achieved a BMI reduction substantial enough to transition below the clinical threshold for obesity based on standardized age- and sex-specific growth charts. In contrast, 100% of participants receiving placebo remained categorized as having obesity at week 68.
The observed tolerability and adverse-event profile of semaglutide aligned with data established in previous pediatric and adult clinical trials of semaglutide and liraglutide (Saxenda). Reassuringly, the investigators reported no detrimental signals or safety concerns regarding linear growth or pubertal maturation.
Table 2. Comparative Efficacy and Safety Outcomes at Week 68
| Clinical End Point / Metric | Semaglutide + Lifestyle (n=165 total cohort) | Placebo + Lifestyle |
| BMI Percentage Change | Significantly greater reduction vs placebo | Minimal change / inferior to active drug |
| Resolution of Obesity Classification* | 40.4% of participants | 0.0% (100% retained obesity diagnosis) |
| Pubertal & Skeletal Growth Effects | No adverse impact observed | No adverse impact observed |
| Overall Safety & Tolerability Profile | Consistent with prior pediatric/adult GLP-1 RA trials | Consistent with placebo controls |
*Defined as falling below the threshold for pediatric obesity on standardized, age- and sex-specific BMI growth percentiles.
Clinical Implications and Expert Perspectives
These pediatric outcomes build upon data from the landmark STEP TEENS trial, which demonstrated a 16.1% mean BMI reduction at 68 weeks in adolescents aged 12 to 17 years receiving semaglutide 2.4 mg once weekly, a regimen that secured US Food and Drug Administration (FDA) approval in December 2022.
Emphasizing the importance of intervening during early childhood, Dr. Ania M. Jastreboff, professor of medicine (endocrinology) and pediatrics (pediatric endocrinology) at Yale University and director of the Yale Obesity Research Center, observed:
โChildhood obesity is particularly concerning due to both immediate and enduring impacts on health, including a strong predilection to adult obesity and increased risk for the early emergence of obesity-related complications.โ
Dr. Jastreboff further contextualized the clinical magnitude of these findings within this young cohort:
โMost of the children in the STEP Young trial were classified as having severe 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.โ
Complete secondary efficacy metrics, detailed tolerability parameters, and subgroup analyses from the STEP Young trial are scheduled for formal presentation at ObesityWeek in November.
