Novo Nordisk reported on 7 September that 40.4% of children aged 6 to under 12 who took once-weekly semaglutide in its STEP Young trial were no longer classified as having obesity after 68 weeks, compared with none of the children given placebo. Every child in both arms also followed a reduced-calorie diet and an exercise programme, and the trial met its primary endpoint. What has been released is a company announcement rather than a peer-reviewed paper, and no GLP-1 medicine is currently approved in the United States for obesity in children under 12.
What the trial measured
STEP Young randomised 165 children aged 6 to under 12 with obesity to once-weekly subcutaneous semaglutide or placebo, double-blind, across multiple countries. Novo describes the maximum dose as either 1.7 mg or 2.4 mg, assigned by the child’s weight at the start of the trial. The primary endpoint was the percentage change in body mass index from baseline to week 68; the confirmatory secondary endpoint was whether a child’s BMI classification improved over the same period.
Obesity in children is defined by percentile rather than by an absolute BMI number, because children are still growing: a BMI at or above the 95th percentile for age and sex. More than 85% of the children entering STEP Young had class II or class III obesity, meaning at or above 120% and 140% of that 95th percentile, which Novo equates to adult BMIs of roughly 35 and 40. Against that starting point, 40.4% finishing below the obesity threshold is the headline number. It is calculated on the trial product estimand, which is the effect estimated if every child had stayed on treatment throughout.
The release does not give the randomisation ratio, so the number of children behind that 40.4% is not stated. With 165 randomised in total, the semaglutide arm could be anywhere from roughly 80 to roughly 110 children, which would put 40.4% of it somewhere between about 32 and 45 individuals. The announcement also does not report the actual BMI change for the primary endpoint, only that it beat placebo. Novo says overall safety and tolerability matched earlier adult and adolescent semaglutide trials, with no new safety concerns identified and none specific to growth or pubertal development.
This age band is the reason the trial exists. Semaglutide is already approved for obesity from age 12, and the STEP Young programme was run under post-marketing requirements attached to that approval. A positive result in 6 to 11 year olds is the step that would put a regulatory filing for the younger group on the table, which is why the number matters well beyond the 165 children in it.
What is not yet known
Almost everything a reader would need in order to judge the size of the benefit is still unpublished: no BMI percentage change, no confidence intervals, no adverse-event table, no dropout rate. Detailed results are scheduled for ObesityWeek 2026 in Washington DC on 14 to 17 November, and until then this is a manufacturer’s topline about its own product rather than evidence that has been through review. Sixty-eight weeks is also short measured against a childhood, and the announcement says nothing about what happens after treatment stops, which in adults has been the difficult part. Growth and puberty were reported as unaffected, but 165 children is a small sample in which to rule out uncommon developmental effects.
Sources: Novo Nordisk, “Novo Nordisk STEP Young phase 3 data: 40.4% of children living with obesity achieved a BMI below the obesity threshold with semaglutide and lifestyle modification”, company press release, 7 September 2026. Approval ages for GLP-1 receptor agonists in young people are as stated in O’Brien EM and colleagues, British Journal of Anaesthesia, 8 September 2026 (doi:10.1016/j.bja.2026.07.016).
