What STEP-TEENS Showed: Semaglutide for Adolescents with Obesity

Adolescent obesity has been one of the most stubborn problems in pediatrics. Lifestyle intervention works for some kids, fails for most, and bariatric surgery has been the only consistently effective intervention available below the age of 18 — a high bar that most families never reach. The STEP-TEENS trial, published in the New England Journal of Medicine on November 2, 2022 [1], changed that calculus. 201 adolescents aged 12-17 randomized to weekly semaglutide 2.4 mg or placebo for 68 weeks produced a 16.7-percentage-point separation in BMI change — the largest pharmacological pediatric weight loss result ever recorded. The FDA approved the adolescent indication seven weeks later [2], and the American Academy of Pediatrics' 2023 Clinical Practice Guideline now formally recommends pharmacotherapy as adjunct treatment for adolescents with obesity [3]. This article walks through the verified trial data, the AAP recommendation, and the open long-term safety question that hasn't yet been answered.

The clinical context: how big the adolescent obesity problem is

According to the most recent CDC NHANES data, approximately 21.2% of US adolescents aged 12-19 have obesity [4]. That's roughly one in five, and the rate has been rising for decades despite consistent public health attention. Adolescents with obesity carry an elevated lifetime risk of type 2 diabetes, hypertension, sleep apnea, cardiovascular disease, NAFLD/MASLD, depression, and orthopedic complications — many of which begin to manifest before adulthood.

The standard treatment paradigm before STEP-TEENS was tiered: intensive lifestyle and behavioral intervention as first line, with metabolic and bariatric surgery available as a last resort for adolescents with severe obesity (BMI ≥120% of the 95th percentile) [3]. There were a few FDA-approved pharmacotherapies for adolescents (orlistat, phentermine/ topiramate, liraglutide), but none had produced the magnitude of effect that bariatric surgery delivers, and uptake was limited.

STEP-TEENS was designed to test whether the same semaglutide 2.4 mg dose that produces ~15% body weight loss in adults (STEP-1) would deliver comparable results in the adolescent population.

STEP-TEENS trial design

STEP-TEENS was a phase 3, double-blind, randomized, placebo- controlled trial conducted at sites across the US, Europe, Mexico, and the Russian Federation [1]. Key design parameters:

• Sample size: 201 adolescents randomized 2:1 (134 to semaglutide, 67 to placebo)
• Age range: 12 to less than 18 years at screening
• Inclusion criteria: BMI at or above the 95th percentile for age and sex (the pediatric definition of obesity), OR BMI at or above the 85th percentile WITH at least one weight-related comorbidity
• Drug: Semaglutide 2.4 mg subcutaneously once weekly — the same maintenance dose used in adults
• Escalation schedule: Identical to the adult STEP protocol — 0.25 mg → 0.5 mg → 1.0 mg → 1.7 mg → 2.4 mg, with 4-week increments
• Duration: 68 weeks of active treatment plus a 7-week off-treatment follow-up period (total 75 weeks)
• Lifestyle intervention: All participants in both arms received intensive behavioral counseling on diet and physical activity throughout the trial
• Primary endpoint: Percent change in BMI from baseline to week 68 (the standard pediatric weight loss outcome — adolescents are still growing, so absolute weight is less interpretable than BMI percentile)

The primary result

STEP-TEENS hit its primary endpoint by a margin large enough to change the standard of care immediately [1]:

Two things stand out. First, the magnitude is comparable to what STEP-1 reported in adults — the adolescent effect size is not meaningfully smaller than the adult effect size, despite the population being still growing and metabolically distinct from adults. Second, the placebo arm gained a small amount of BMI on average, which is what you'd expect in untreated adolescent obesity (the natural history is gradual progression, not stability). The difference between the two arms is therefore even larger than the semaglutide-arm number alone suggests.

The 73% “clinically meaningful response” rate (defined as ≥5% BMI reduction) is the most clinically actionable number in the table. In adolescent weight loss trials before STEP-TEENS, the equivalent response rate was typically in the 10-25% range. STEP-TEENS roughly tripled that.

Secondary endpoints

The published trial reports that semaglutide produced significant improvements over placebo across the prespecified secondary endpoints, including waist circumference, glycated hemoglobin (HbA1c), the lipid panel (LDL, triglycerides), alanine aminotransferase (ALT, a liver function marker that captures NAFLD/MASLD progression), and patient-reported health-related quality of life [1]. The exact numerical magnitudes for each secondary endpoint are detailed in the full NEJM publication and supplementary appendix; we're reporting at the level of statistical direction here because the published abstract verifies the direction but the granular per-endpoint magnitudes require full-text access.

Adverse events: pediatric-specific patterns

STEP-TEENS's adverse event profile was broadly similar to the adult STEP-1 trial — predominantly gastrointestinal, predominantly mild to moderate, predominantly resolving with continued use. Specific reported rates [1]:

Two pediatric-specific patterns are worth flagging. First, the cholelithiasis rate of ~4% in the semaglutide arm vs 0% in placebo is notable — adult STEP trials reported cholelithiasis at lower rates and over longer follow-up. The adolescent population may be more susceptible to gallstone formation during rapid weight loss, possibly because the underlying weight loss trajectory is faster than in adults. Second, the published label notes that cholelithiasis, cholecystitis, hypotension, rash, and urticaria were more commonly reported in adolescents than in adults on semaglutide [6]. None of these are dealbreakers, but they change the monitoring conversation between prescriber and family.

For the adult adverse event picture by comparison, see our GLP-1 side effects investigation.

The FDA approval and the AAP endorsement

The FDA approved Wegovy (semaglutide 2.4 mg) for chronic weight management in adolescents 12 years and older with obesity on December 23, 2022 [2] — less than two months after STEP-TEENS was published. The approval expanded the existing Wegovy indication to include adolescents with BMI at or above the 95th percentile for age and sex.

The American Academy of Pediatrics published its 2023 Clinical Practice Guideline for the Evaluation and Treatment of Children and Adolescents With Obesity in January 2023 [3]. The guideline formally recommends that physicians offer adolescents 12 years and older with obesity weight-loss pharmacotherapy as adjunct to intensive health behavior and lifestyle treatment, based on indications, risks, and benefits. This was a notable shift from the prior watch-and-wait approach that had dominated pediatric obesity care for decades. The AAP guideline also formalized the recommendation that adolescents 13 and older with severe obesity (BMI ≥120% of the 95th percentile) should be evaluated for metabolic and bariatric surgery [3].

Tirzepatide for adolescents: still in trial

Tirzepatide is not yet FDA-approved for use in adolescents. Eli Lilly is running a phase 3 trial called SURMOUNT-ADOLESCENTS-2 (NCT06439277) [5] in adolescents 12-17 with obesity and at least two weight-related comorbidities. The trial is double-blind, randomized, placebo-controlled, and expected to run roughly 76 weeks. As of this writing the trial is ongoing; results have not been published. Until they are, semaglutide remains the only FDA-approved GLP-1 / GIP-GLP-1 agonist for adolescent obesity.

The big open question: long-term safety

STEP-TEENS gave us 68 weeks of randomized data plus a 7-week off-treatment follow-up. That's the longest controlled adolescent semaglutide dataset we have. The follow-up phase showed that adolescents in the semaglutide arm regained some BMI after stopping treatment (similar to the adult withdrawal pattern documented in our STEP-4 / STEP-1 extension investigation), but the trial was not designed to measure the multi-year consequences of pediatric semaglutide use that the medication will increasingly need to support.

The most important unanswered questions for the field over the next several years:

1. Bone density and skeletal development. STEP-TEENS did not directly measure bone mineral density. GLP-1 therapy produces rapid weight loss, and rapid weight loss in any population is associated with reduced bone density. In adolescents, who are still building peak bone mass (typically achieved in the late teens to early 20s), this is a more pressing question than in adults. There is an ongoing trial specifically designed to measure adolescent semaglutide effects on bone outcomes (NCT07165158), but published results are not yet available.
2. Linear growth. STEP-TEENS did not report linear growth (height) outcomes as a primary or secondary endpoint. The trial was 68 weeks, which is short relative to the adolescent growth window. Whether years of GLP-1 therapy during the active growth years affects final adult height is an unanswered question.
3. Long-term durability and cycling. Adult STEP-1 extension data shows ~67% weight regain within one year of discontinuation. If adolescents stop semaglutide when they age out of pediatric care or lose insurance coverage, the same regain pattern is likely. What does repeated cycling of GLP-1 therapy across adolescence and young adulthood do to long-term metabolic health? No published data exists.
4. Mental health. Adolescent obesity is frequently comorbid with depression and anxiety, and the relationship between weight loss medications and mental health outcomes in adolescents is not well-characterized in published trials. STEP-TEENS reported no statistically significant signal in either direction, but the trial was not powered for mental health endpoints.

What this means for adolescents and their families

For adolescents 12 and older with documented obesity (BMI ≥ 95th percentile) who have not achieved meaningful weight loss with intensive lifestyle and behavioral intervention, semaglutide is now an evidence-based, FDA-approved, AAP- recommended option backed by a large randomized trial. The magnitude of effect is comparable to adult dosing, and the adverse event profile is broadly similar — with the notable addition of higher rates of cholelithiasis, rash, and urticaria in the adolescent population.

The long-term unknowns matter, and any prescribing decision should be made with clear acknowledgment that we don't yet have multi-year follow-up data on bone density, linear growth, mental health, or what happens when adolescents on therapy age into adulthood. Those are questions the field will answer over the coming decade. In the meantime, semaglutide for adolescents is a meaningful clinical option for a meaningful clinical problem — used carefully, monitored closely, and discussed honestly with families about both the benefits and the open questions.

For the broader picture of how GLP-1 therapy fits into modern obesity treatment, see our pricing index and our editorial coverage of the adult cardiovascular outcomes evidence (SELECT). For the related drug class, see the tirzepatide vs semaglutide head-to-head deep dive.