Primary results from the STEP Young trial
- In the Phase 3 STEP Young trial, 40.4% of children who received weekly semaglutide moved below the obesity body mass index (BMI) threshold after 68 weeks of treatment.
- In the placebo group, 0% (none) of the participants achieved a BMI below the obesity cutoff during the same 68-week period.
- The study evaluated 165 children aged 6 to under 12 years old, with more than 85% starting the trial with severe obesity.
- Both treatment arms received lifestyle counseling that included a reduced-calorie diet and increased physical activity.
- Novo Nordisk (NYSE: NVO) announced plans to present full clinical data at ObesityWeek 2026 in Washington, D.C., scheduled for November 14-17, 2026.
| Finding | Plain-English meaning |
|---|---|
| 40.4% of semaglutide participants fell below the obesity threshold | Four out of ten children who received the weekly injection lowered their body mass index enough to no longer qualify as having obesity after 68 weeks. |
| 0% of placebo participants reached a BMI below the obesity threshold | No children who received only lifestyle counseling without active medication dropped below the obesity boundary during the trial. |
| Over 85% of trial participants entered with Class II or Class III severe obesity | Most children in the study started with high levels of excess body weight, corresponding to adult BMI values of 35 or higher. |
Key metrics from the pediatric trial
| Variable | Value reported in research brief |
|---|---|
| Clinical trial name | STEP Young (Phase 3) |
| Study size | 165 children |
| Age bracket | 6 to under 12 years old |
| Severe obesity rate at baseline | Greater than 85% (Class II or Class III) |
| Active regimen | Subcutaneous semaglutide once weekly (1.7 mg or 2.4 mg max) |
| Treatment duration | 68 weeks |
| Primary outcome success (semaglutide) | 40.4% reached BMI below obesity threshold |
| Primary outcome success (placebo) | 0% reached BMI below obesity threshold |
Understanding GLP-1 receptor agonists in pediatric health
Pediatric healthcare providers face a growing challenge when treating severe childhood obesity. Standard lifestyle management, such as diet modifications and physical activity routines, remains the baseline approach. Yet, metabolic adaptations often make it difficult for children with high initial body weights to maintain significant long-term reduction through lifestyle steps alone. Severe obesity in children is defined relative to adult BMI benchmarks. Class II severe obesity matches an adult BMI of at least 35, whereas Class III severe obesity corresponds to an adult BMI of 40 or higher.
The drug evaluated in the trial, semaglutide, is a glucagon-like peptide-1 (GLP-1) receptor agonist. GLP-1 is a naturally occurring gut hormone involved in appetite regulation and blood sugar control. Semaglutide works as an analogue of this hormone, binding to central nervous system receptors that govern hunger and food intake. Think of GLP-1 signaling as a dial that turns down appetite signals after eating. By activating these pathways, the medication helps reduce overall calorie intake by increasing sensations of fullness.
In adult clinical care, semaglutide is already used at various doses for type 2 diabetes and chronic weight management. Applying GLP-1 therapy to younger pediatric populations requires careful evaluation because growing children undergo ongoing bone, muscle, and organ development.
Analyzing the STEP Young trial design and efficacy
The Phase 3 STEP Young clinical trial examined the safety and efficacy of semaglutide specifically in younger children. The trial enrolled 165 children aged 6 to under 12 years old. At enrollment, more than 85% of these young participants were classified as having severe obesity (Class II or Class III).
Participants were randomly assigned to receive either once-weekly subcutaneous (under-the-skin) injections of semaglutide or a matching placebo injection. Depending on baseline body weight, children in the active group were escalated to a maximum weekly dose of either 1.7 mg or 2.4 mg. Both groups received structured lifestyle interventions consisting of a reduced-calorie diet and regular exercise recommendations throughout the 68-week period, which spans approximately 1.3 years.
By week 68, 40.4% of children in the semaglutide group reduced their BMI percentile into a category below the clinical obesity threshold. Meanwhile, 0% of children in the placebo group achieved this outcome.
Ania M. Jastreboff, Professor of Medicine and Pediatrics at Yale and Director of the Yale Obesity Research Center, contextualized the findings: “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.”
Comparing pediatric outcomes to adult clinical benchmarks
To evaluate how these pediatric results compare with adult research, scientific teams look at broader data from the Semaglutide Treatment Effect in People with Obesity (STEP) program. In the STEP 1 adult trial published in The New England Journal of Medicine, 1961 adults with overweight or obesity without diabetes received once-weekly semaglutide (2.4 mg) or placebo for 68 weeks. Adults taking semaglutide achieved a mean body weight change of -14.9%, compared to -2.4% in the placebo group.
Longer adult trials demonstrate how weight trajectories behave over time. In STEP 5, adults taking semaglutide 2.4 mg maintained a mean weight reduction of -15.2% at 104 weeks, compared to -2.6% for placebo. In adult populations with type 2 diabetes evaluated in STEP 2, once-weekly semaglutide 2.4 mg achieved a mean body weight loss of 9.6%, compared to 3.4% in the placebo group.
While adult studies primary endpoints often measure percentage change in total body weight, pediatric studies evaluate BMI percentiles relative to age and sex growth charts. Because children naturally grow in height, BMI percentile shifts provide a standardized measure of weight trajectory during childhood growth spurts.
Evaluating safety profiles and growth markers
Safety monitoring remains a primary focal point in pediatric clinical trials. Analysts evaluated whether continuous weekly GLP-1 administration impacted growth trajectories or physical maturation in young children.
Trial investigators reported no new safety concerns during the STEP Young study. Researchers identified no adverse issues related to childhood growth or pubertal development across the 68 weeks. Overall safety and tolerability matched the established profiles observed in previous pediatric and adult trials of GLP-1 receptor agonists, including semaglutide and liraglutide, an older daily GLP-1 analogue developed by Novo Nordisk.
In adult trials such as STEP 1, gastrointestinal events were the most frequently reported side effects. Symptoms like nausea and diarrhea were generally mild to moderate, transient, and diminished over time. In that adult study, 4.5% of participants receiving semaglutide discontinued treatment due to gastrointestinal side effects, compared to 0.8% in the placebo group. Specific side-effect frequency rates for the STEP Young cohort were not detailed in the preliminary announcement.
What the data cannot answer yet
Public health metrics highlight the scale of early childhood weight management challenges. An estimated 177 million children aged 5 to 19 were living with obesity worldwide in 2025. Projections indicate this number could reach 228 million by the year 2040.
Despite the 40.4% success figure reported in the trial announcement, several key data points remain unreleased. The initial report did not specify the average total percentage of body weight lost by the children or the mean numerical drop in BMI points. Specific rates of gastrointestinal side effects for this 6 to 11 age bracket were also omitted from the early summary. Furthermore, the coverage did not provide trading figures or market movement metrics for Novo Nordisk stock.
The trial evidence demonstrates efficacy over 68 weeks as an adjunct to diet and exercise. However, long-term post-trial maintenance data for this specific age group are not yet available in published literature.
Next scientific milestones and presentation timeline
Novo Nordisk announced that comprehensive trial data will be formally presented at an upcoming medical conference. The company selected The Obesity Society’s ObesityWeek 2026 annual meeting for its full data presentation.
The meeting is set to take place on November 14-17, 2026, in Washington, D.C. The full data set is expected to provide broken-down safety sub-analyses, changes in body composition, and exact metabolic marker changes. The initial coverage did not outline specific target dates for regulatory submissions to the U.S. Food and Drug Administration or European regulatory agencies.
Related Coverage
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Sources:
- Yahoo News, “Novo Nordisk Semaglutide Trial Shows 40.4% of Children Moved Below Obesity BMI Threshold” (https://www.yahoo.com/news/science/articles/novo-nordisk-semaglutide-trial-shows-120847949.html)
- The New England Journal of Medicine, “Once-Weekly Semaglutide in Adults with Overweight or Obesity” (https://www.nejm.org/doi/full/10.1056/NEJMoa2032183)
- PubMed Central, “Semaglutide for the treatment of overweight and obesity: A review” (https://pmc.ncbi.nlm.nih.gov/articles/PMC10092086/)
Disclaimer: This article is for general information only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about any medical condition or before making health decisions.