STEP-TEENS Trial: A Plain-English Overview of What It Established
At a glance
| Detail | Value | |---|---| | Trial name | STEP-TEENS (Semaglutide Treatment Effect in People with Obesity, Adolescents) | | N | 201 | | Population | Adolescents aged 12-17, BMI ≥ 95th percentile (or ≥ 85th with a weight-related comorbidity) | | Intervention | Subcutaneous semaglutide 2.4 mg once weekly | | Comparator | Matched placebo injection once weekly | | Duration | 68 weeks on treatment + 7-week follow-up (75 weeks total) | | Primary endpoint | Change in BMI from baseline to week 68 | | Key result | -16.1% BMI change with semaglutide vs. +0.6% with placebo (estimated treatment difference: -16.7 percentage points; p < 0.001) | | Registration | NCT04102685 |
Why This Trial Was Needed
Before STEP-TEENS, clinicians treating adolescents with severe obesity had very few pharmacotherapy options. Orlistat had marginal efficacy and poor tolerability. Phentermine carried age restrictions. Bariatric surgery worked but carried surgical risk and was often refused by families. The adult STEP program had already demonstrated that semaglutide 2.4 mg produced roughly 15% weight loss in adults, but no one had tested this dose in teenagers. Adolescent obesity prevalence in the U.S. had risen past 20%, and the clinical consequences (type 2 diabetes, hypertension, fatty liver disease) were appearing at younger ages. A rigorous placebo-controlled trial in this age group was overdue.
Who Got Into the Trial
Investigators enrolled 201 adolescents across 45 sites in multiple countries. To qualify, participants had to be 12 to <18 years old with a BMI at or above the 95th percentile for age and sex (the clinical definition of obesity in this age group). Alternatively, those at or above the 85th percentile could enter if they had at least one weight-related comorbidity. Participants were required to have had at least one unsuccessful attempt at weight management. The published trial excluded adolescents with type 1 diabetes, a BMI above 60 kg/m², or those using other weight-loss medications.
Randomization was 2:1, meaning 134 adolescents received semaglutide and 67 received placebo. All participants also received standardized lifestyle intervention: counseling on nutrition, physical activity, and behavioral strategies throughout the 68-week treatment period.
How the Drug Was Given
Semaglutide was escalated over 16 weeks following the same dose-titration schedule used in adults:
| Weeks | Weekly dose | |---|---| | 1-4 | 0.25 mg | | 5-8 | 0.5 mg | | 9-12 | 1.0 mg | | 13-16 | 1.7 mg | | 17-68 | 2.4 mg (maintenance) |
The injection was subcutaneous, given once per week on the same day each week. The gradual ramp exists to reduce gastrointestinal side effects, which are the most common complaint with all GLP-1 receptor agonists.
What Was Measured
The primary endpoint was percent change in BMI from baseline to week 68. In adults, most obesity trials use percent change in body weight. In adolescents, BMI is the standard because teenagers are still growing in height, and raw weight change does not account for normal growth.
Key secondary endpoints included:
- Proportion of participants achieving ≥5% BMI reduction
- Proportion achieving ≥10% BMI reduction
- Change in body weight (kg)
- Change in waist circumference
- Change in BMI z-score (which adjusts for age and sex norms)
The HealthRX STEP-TEENS Results Breakdown
Primary Outcome
The semaglutide group achieved a mean BMI reduction of 16.1% from baseline to week 68. The placebo group saw a mean BMI increase of 0.6%. The estimated treatment difference was -16.7 percentage points (95% CI: -20.3 to -13.2; p < 0.001).
To put this number in perspective: a 16% BMI reduction in a teenager who starts at a BMI of 37 translates to roughly a 6-point drop, from a BMI of 37 to about 31. That is the difference between Class II obesity and the upper boundary of overweight.
Categorical Responders
| BMI reduction threshold | Semaglutide | Placebo | |---|---|---| | ≥5% | 73% | 18% | | ≥10% | 62% | 9% | | ≥15% | 37% | 3% | | ≥20% | 27% | 0% |
Nearly three in four adolescents on semaglutide lost at least 5% of their BMI. More than one in four lost 20% or more. In the placebo arm, not a single participant reached the 20% threshold.
Body Weight and Waist Circumference
Mean body weight decreased by 15.3 kg with semaglutide compared to a gain of 2.3 kg with placebo. Waist circumference dropped by 7.7 cm more in the semaglutide group. These are clinically meaningful changes. A reduction of this magnitude in waist circumference is associated with improved cardiometabolic risk markers in both adult and pediatric populations.
BMI z-Score
The BMI z-score, which compares a teenager's BMI to population norms for their age and sex, dropped by 0.90 points more in the semaglutide group than in the placebo group. For context, a z-score reduction of that size can move an adolescent from severe obesity into the moderate obesity or overweight range when calibrated against CDC growth charts.
Safety Profile
Semaglutide's side-effect pattern in adolescents was consistent with what the adult STEP trials had documented.
| Adverse event | Semaglutide (%) | Placebo (%) | |---|---|---| | Nausea | 36 | 13 | | Vomiting | 18 | 7 | | Diarrhea | 18 | 10 | | Abdominal pain | 10 | 7 | | Any GI event | ~62 | ~42 |
Most gastrointestinal events were mild to moderate and occurred during the dose-escalation phase. They generally resolved without treatment discontinuation. 6 participants (4.5%) in the semaglutide group discontinued due to adverse events, compared to none in the placebo group.
There were no cases of pancreatitis, medullary thyroid carcinoma, or major adverse cardiovascular events. Five serious adverse events were reported in the semaglutide group, but the investigators judged none to be treatment-related. No clinically significant changes in linear growth velocity were observed during the 68-week treatment period, an important concern specific to pediatric trials.
Limitations Worth Knowing
The trial had several limitations the authors and subsequent reviewers noted:
Short duration relative to the disease. Obesity is a chronic condition. Sixty-eight weeks of treatment is long enough to demonstrate efficacy but not long enough to answer questions about durability. The 7-week off-treatment follow-up showed rapid weight regain, consistent with what the adult STEP trials found after discontinuation.
Narrow demographics. The majority of participants were White and from high-income countries. Whether these results generalize to all racial, ethnic, and socioeconomic groups is uncertain.
Small sample size. With only 201 participants, the trial was powered for the primary BMI endpoint but was too small to detect rare adverse events. Events like pancreatitis or thyroid neoplasia occur at rates that require thousands of patient-years to quantify.
No pubertal staging analysis. The trial did not report separate outcomes by Tanner stage, so we do not know whether pubertal status modifies the treatment effect.
All participants received lifestyle counseling. This is good clinical practice, but it means the results cannot be attributed to the drug alone. It also means the results may be less impressive in real-world settings where lifestyle support is less structured.
What Happened After the Trial
The results from STEP-TEENS contributed directly to the FDA's December 2022 expansion of the Wegovy (semaglutide 2.4 mg) label to include adolescents aged 12 and older. This made semaglutide one of only a few FDA-approved anti-obesity medications for this age group.
The American Academy of Pediatrics released clinical practice guidelines in January 2023 recommending pharmacotherapy as part of a comprehensive treatment approach for adolescents with obesity. These guidelines cited STEP-TEENS as supporting evidence for GLP-1 receptor agonist use in this population. The shift was significant: prior AAP guidance had focused almost exclusively on lifestyle modification and surgery.
Real-world insurance coverage remains inconsistent. Many commercial plans and state Medicaid programs still exclude anti-obesity medications for adolescents, or impose prior authorization requirements that create barriers to access. The drug's list price (roughly $1,300 per month without insurance) makes out-of-pocket use prohibitive for most families.
How to Read This Trial Critically
STEP-TEENS answered a specific question: does semaglutide 2.4 mg reduce BMI in adolescents with obesity over 68 weeks? The answer is clearly yes, with an effect size comparable to what was seen in adults. But several questions remain unanswered.
First, long-term safety data in growing adolescents does not yet exist. The concern about thyroid C-cell tumors, which appears as a boxed warning on the Wegovy label, is based on rodent studies. Whether this risk applies to humans, particularly adolescents with decades of potential exposure ahead, is unknown.
Second, the trial did not address what happens with multi-year use. The weight regain observed during the short follow-up period suggests that, like adult obesity, treatment may need to be ongoing. This creates questions about adherence, cost, and the psychological impact of indefinite injection therapy starting in adolescence.
Third, the 2:1 randomization means only 67 adolescents received placebo. While the between-group difference was large enough to be statistically strong, the placebo arm is small enough that its mean outcome could be influenced by a few outliers.
Bottom Line for Clinicians
STEP-TEENS demonstrated that semaglutide 2.4 mg produces clinically significant BMI reduction in adolescents aged 12-17 with obesity. The magnitude of effect (16.1% BMI reduction) and the responder rates (73% achieving ≥5% reduction) are strong. The safety profile was consistent with adult data, with no new signals of concern over 68 weeks. The key clinical limitations are the lack of long-term safety and durability data and the practical barriers of cost and insurance coverage. For adolescents with severe obesity and weight-related comorbidities who have not responded to lifestyle intervention alone, this trial provides the evidence base for discussing semaglutide as a treatment option.
Frequently asked questions
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References
- Weghuber D, Barrett T, Gies I, et al. Once-weekly semaglutide in adolescents with obesity. N Engl J Med. 2022;387(24):2245-2257. PubMed
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed
- Wegovy (semaglutide) prescribing information. Novo Nordisk. Revised 2022. FDA Label
- 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(2):e2022060640. PubMed
- Kelly AS, Auerbach P, Barrientos-Perez M, et al. A randomized, controlled trial of liraglutide for adolescents with obesity. N Engl J Med. 2020;382(22):2117-2128. PubMed