The STEP TEENS trial found that average BMI fell 16.1% with semaglutide and rose 0.6% with placebo over 68 weeks. BMI, or body mass index, measures weight relative to height. Both groups received food and activity counseling. The result describes teenagers in a supported trial, not what any one teenager will experience.
For a family, the next questions matter just as much: who was studied, what side effects occurred, and what remains unknown? Treatment decisions belong with the teenager, their family, and a pediatric clinician.
What question did the STEP TEENS trial ask?
Could weekly semaglutide injections, added to lifestyle counseling, reduce BMI more than counseling with placebo, an inactive injection? Daniel Weghuber and colleagues reported the study in the New England Journal of Medicine in 2022.
The trial enrolled 201 adolescents aged 12 to under 18. Their average age was 15.4. They were assigned by chance: 134 to semaglutide and 67 to placebo. Families and investigators didn't know the assignments.
Entry required obesity, defined as BMI at or above the 95th percentile for age and sex. The trial also allowed BMI at or above the 85th percentile with a weight-related condition. Only one participant entered with overweight, so the results chiefly describe obesity.
A BMI percentile shows where a child's BMI sits compared with children of the same age and sex. The registration, NCT04102189, records the eligibility rules, including exclusion of children who hadn't started puberty.
Major depression within two years, severe psychiatric disorders, bulimia nervosa (an eating disorder) and a previous suicide attempt were among the paper's exclusions. That limits what its findings can say about those teenagers.
Families received lifestyle counseling before randomization, meaning assignment by chance, and throughout treatment.
STEP TEENS results: what the BMI figures mean
The primary endpoint, the main measurement chosen beforehand, was percentage change in BMI. It differs from percentage weight loss because height can change during adolescence.
The headline figures use the treatment policy estimand: the treatment effect being estimated regardless of treatment stops or other weight-management treatment. Missing measurements were estimated. Our estimand explainer describes why that choice matters.
| Measurement at week 68 | Semaglutide | Placebo |
|---|---|---|
| Average BMI change | −16.1% | +0.6% |
| BMI z-score change | −1.1 | −0.1 |
A BMI z-score expresses distance from the reference average in units that account for how much BMI varies. It isn't a percentage. The paper's estimated gap in percentage BMI change was 16.7 percentage points, the gap between the two percentages.
Adults have a separate evidence base. The STEP 1 results guide covers that trial; teenager results cannot replace adult findings or establish outcomes for a compounded preparation.
What side effects appeared?
About 6 in 10 semaglutide participants reported stomach or bowel problems, compared with about 4 in 10 on placebo. Most were mild or moderate.
An adverse event is a health problem recorded during a trial; recording it doesn't prove the medicine caused it. The following figures come from the paper's safety results. That group included 133 semaglutide participants and 67 placebo participants who received treatment.
| Recorded event or treatment stop | Semaglutide | Placebo |
|---|---|---|
| Stomach or bowel events | 62% | 42% |
| Nausea | 56 (42%) | 12 (18%) |
| Vomiting | 48 (36%) | 7 (10%) |
| Diarrhea | 29 (22%) | 13 (19%) |
| Gallstones | 5 (4%) | 0 |
| Serious adverse events | 15 (11%) | 6 (9%) |
| Stopped treatment because of adverse events | 6 (5%) | 3 (4%) |
| Stopped because of stomach or bowel events | 3 (2%) | 1 (1%) |
The paper rounded these percentages to whole numbers. Gallstones are hardened deposits in the gallbladder. One affected participant also had gallbladder inflammation. Serious events include problems such as those requiring hospitalization.
What later analyses added
About 45% of semaglutide participants reached a BMI category below obesity, compared with about 12% on placebo. The exact figures were 44.9% and 12.1%. Kelly and colleagues, Obesity, 2023, reported this in a post hoc analysis, meaning an additional analysis after the original trial. Crossing a category boundary doesn't mean every health concern has disappeared.
A Diabetes Care analysis by Arslanian and colleagues examined 193 participants without type 2 diabetes, a condition that raises blood sugar. It appeared online November 26, 2025, and in the June 2026 issue. Insulin resistance means the body responds less readily to insulin, the hormone that helps manage blood sugar. HOMA-IR, a blood-test estimate of that resistance, fell 35.0% with semaglutide versus 5.3% with placebo. Several blood-fat and liver-test measures also improved. These were additional analyses of the same trial, not a new trial proving prevention of diabetes or heart disease.
What researchers still wanted answered
The trial authors called for longer treatment and follow-up. Seven weeks after treatment ended, some BMI reduction had already been lost, despite continued lifestyle support. That short window cannot show the long-term pattern after stopping.
The paper found no concerning changes in growth or puberty during the trial. It cannot settle those questions across years of development. A 2024 review by Bensignor, Arslanian, and Vajravelu also emphasized limited long-term adolescent safety data and weight regain after stopping.
Novo Nordisk funded the trial and participated in its design and analysis. Its selected participants and structured support matter when interpreting the averages.
The current label and newer pediatric news
As of October 1, 2026, the day this article was written, the Wegovy prescribing information says “Revised: 06/2026.” Sections 1 and 8.4 cover injection treatment for obesity from age 12, alongside a reduced-calorie diet and increased activity. They say safety and effectiveness for weight reduction below age 12 have not been established.
Novo's September 7, 2026 announcement reported separate STEP Young findings in younger children. Those company-reported results don't change the label by themselves. The semaglutide for children guide covers that development and Promise's age boundary.
As of October 1, 2026, the day this article was written, Northwestern's September 21 release also highlighted nutrient-deficiency diagnoses in young GLP-1 users. GLP-1 medicines copy a gut hormone's fullness signal. The study counted insurance records across several medicines; it doesn't establish that semaglutide caused deficiencies. Our children's nutrition guide explains that separate evidence.
What this means for compounded prescriptions
STEP TEENS didn't test Promise's preparation. Through Promise, semaglutide is dispensed as a compounded medication, prepared by a pharmacy for a prescription, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. FDA explains that compounded drugs don't undergo its review for safety, effectiveness, or quality before marketing.
A licensed provider may still prescribe — that decision is between you and your doctor.
For adults comparing prescription options, tirzepatide is a different medicine. STEP TEENS did not compare it with semaglutide and cannot decide between them. A pediatric trial also doesn't establish results for either compounded preparation.
The conversation beyond a trial average
For a teenager, a care plan needs room for growth, eating patterns, mental health, family support, and follow-up. A BMI result is one part of that discussion. The pediatric clinician and family decide whether treatment fits; the prescriber sets any actual dose.
At Promise, a licensed provider reviews every request, and not everyone qualifies.
