STEP TEENS published: semaglutide cuts BMI 16.1 percent in adolescents

The New England Journal of Medicine published STEP TEENS, a 68-week randomized, double-blind, placebo-controlled trial of once-weekly semaglutide 2.4 mg in 201 adolescents aged 12 to under 18 with obesity. Mean body-mass index fell 16.1 percent with semaglutide compared with a 0.6 percent increase with placebo ^[1].

Participants had a BMI in the 95th percentile or higher, or a BMI in the 85th percentile or higher plus at least one weight-related condition. All but one participant met the criteria for obesity. They were randomly assigned 2 to 1 to semaglutide or placebo for 68 weeks, and both groups also received a lifestyle intervention. Of the 201 who were randomized, 180 (90 percent) completed treatment ^[1].

The primary endpoint was percentage change in BMI at week 68. The estimated difference between groups was 16.7 percentage points in favor of semaglutide (95 percent confidence interval, -20.3 to -13.2; P<0.001) ^[1]. The secondary confirmatory endpoint was weight loss of at least 5 percent: 95 of 131 participants (73 percent) in the semaglutide group reached that mark versus 11 of 62 (18 percent) on placebo, an estimated odds ratio of 14.0 (95 percent CI, 6.3 to 31.0; P<0.001) ^[1].

Note that some summaries of the trial cite 77 percent versus 20 percent for a BMI reduction of at least 5 percent. The published abstract reports the 73 percent versus 18 percent figures for weight loss of at least 5 percent, which is the endpoint the investigators designated as confirmatory ^[1]. The two measures are not the same thing, and the abstract does not give a figure for the share hitting a 5 percent BMI reduction.

What else the trial measured

Beyond weight, the semaglutide group had greater improvements than placebo in waist circumference, glycated hemoglobin, lipids (except HDL cholesterol), and alanine aminotransferase, a liver enzyme ^[1].

Side effects followed the pattern seen in adult trials. Gastrointestinal adverse events occurred in 62 percent of the semaglutide group versus 42 percent on placebo. Five participants (4 percent) on semaglutide developed gallstones, compared with none on placebo. Serious adverse events were reported in 15 of 133 participants (11 percent) on semaglutide and 6 of 67 (9 percent) on placebo ^[1].

The trial was funded by Novo Nordisk and is registered as NCT04102189 ^[1].

Why it matters for patients

Before STEP TEENS, as the authors put it, "assessment of the drug in adolescents has been lacking" ^[1]. This trial is the evidence base for using semaglutide 2.4 mg in younger patients, and Wegovy's current prescribing information lists an indication to reduce excess body weight and maintain weight reduction long term in adults and pediatric patients aged 12 years and older with obesity, in combination with a reduced-calorie diet and increased physical activity ^[2].

For families, two details of the trial design matter. First, everyone in the study received a lifestyle intervention, so the comparison is medication plus lifestyle support versus lifestyle support alone ^[1]. Second, the results describe average change over 68 weeks; the published figures also show a follow-up period after treatment stopped, and individual results in the waterfall plots varied widely ^[1].

The safety profile is not trivial. Nearly two in three teens on semaglutide had a gastrointestinal side effect, and gallstones appeared only in the semaglutide group ^[1]. Wegovy's label carries a boxed warning about thyroid C-cell tumors seen in rodents, and it is contraindicated in people with a personal or family history of medullary thyroid carcinoma or with multiple endocrine neoplasia syndrome type 2 ^[2]. The label also flags pancreatitis, gallbladder disease, and severe gastrointestinal reactions among its warnings ^[2].

What this trial does not answer is how long teens would need to stay on treatment, what happens to growth and development over many years, or whether the metabolic improvements translate into fewer health problems in adulthood. Those questions were not addressed in the 68-week results ^[1].

What happens next

The NEJM paper later drew published correspondence, with letters and an author reply appearing in the March 23, 2023 issue ^[1]. Wegovy's label has since been revised multiple times, including changes to indications in August and December 2025 and to dosage and administration through March 2026 ^[2]. Coverage and cost for adolescents were not addressed by this trial and remain a separate question for each insurer.