Obesity drugs for children: what a new WHO guideline says and what trials in under-12s and teenagers show

The World Health Organization (WHO) drew a line on October 7. In its first guideline on the subject, it said that children under 10 with obesity are not candidates for the weight-loss drugs now widely used by adults, and that care at that age belongs with diet and activity.

“For children under 10, WHO does not recommend obesity medicines, bariatric surgery or weight-management devices. This is a strong recommendation,” said Luz De Rigil, the agency’s director of nutrition and food safety. Bariatric surgery is surgery on the stomach or gut to bring about weight loss.

The guideline lands in the middle of a fast-moving field. Drug companies are testing the drugs in children as young as six, the BBC reported, and some doctors already prescribe them outside their licensed age range. This explainer sets out what the trials in children and teenagers have found so far, and what they have not looked at.

What the WHO guideline on obesity drugs for children says

The scale of the problem is not in dispute. Estimates suggest 170 million children and adolescents worldwide are obese. Among children aged 5 to 9, obesity prevalence has quadrupled since 1990, rising from 2% to 8%.

The agency’s position rests on age. Below 10, it advises against medicines, surgery and devices. For older children and adolescents, its officials said, these might be appropriate when lifestyle approaches have failed. The agency does not object to research: according to the BBC, WHO officials do not oppose drug trials.

Their stated worry is about what comes after a prescription starts. “We don’t really have evidence that you can use this as a temporary treatment and then turn to something dietary later on in life,” said Laurence Grummer-Strawn, who leads nutrition and food safety actions at WHO. “We are very cautious about jumping in without clear evidence.”

Which obesity drugs have been tested in children

The drugs in question belong to one class, glucagon-like peptide-1 (GLP-1) receptor agonists. They copy a gut hormone that slows the emptying of the stomach and signals fullness to the brain. Two have been through randomized trials in young people. Liraglutide is injected daily. Semaglutide, the newer one, is injected weekly.

Liraglutide was tested first in adults, then in teenagers, then in younger children. Semaglutide has been tested in adults and teenagers. All three of the trials described below were funded by Novo Nordisk, which makes both drugs, and they share several investigators.

Before the youngest of those trials, the cupboard was bare. No medications are currently approved for the treatment of nonmonogenic, nonsyndromic obesity in children younger than 12 years of age, its authors wrote in the New England Journal of Medicine. Nonmonogenic and nonsyndromic together mean ordinary obesity, the kind not traced to a single faulty gene or a named medical syndrome.

What the obesity drug trial in children aged 6 to 11 found

The trial is known as SCALE Kids. It consisted of a 56-week treatment period and a 26-week follow-up period. A total of 82 participants underwent randomization; 56 were assigned to the liraglutide group and 26 to the placebo group. A placebo is a dummy injection. Every child, in both groups, also received help with diet and activity.

The main measure was body mass index (BMI), which is weight in kilograms divided by the square of height in meters. In a growing child, weight alone is misleading, because healthy children get heavier every year.

At week 56, the mean percentage change from baseline in BMI was -5.8% with liraglutide and 1.6% with placebo. The gap between them was 7.4 percentage points, with a plausible range of 3.2 to 11.6.

The weight figures show why BMI is the better guide. The mean percentage change in body weight was 1.6% with liraglutide and 10.0% with placebo. Children on the drug did not lose weight. They gained very little while they grew taller, and the children on placebo gained a tenth of their body weight in a year.

About half of the treated children had a meaningful response. A reduction in BMI of at least 5% occurred in 46% of participants in the liraglutide group and in 9% of participants in the placebo group.

Side effects were common in both groups, and one kind stood out. Gastrointestinal adverse events were more common in the liraglutide group (80% vs. 54%). Gastrointestinal means affecting the stomach and gut: nausea, vomiting, diarrhea. Serious adverse events were reported in 12% and 8% of participants in the liraglutide and placebo groups, respectively.

That is the whole of the randomized evidence in this age group: 56 children on the drug, for one year.

What trials of obesity drugs in teenagers found

The evidence in adolescents is larger and the effects are bigger, especially for the newer drug.

Trial	Age	Drug	Number	Length	Change in BMI, drug	Change in BMI, placebo
SCALE Kids	6 to 11	Liraglutide, daily	82	56 weeks	-5.8%	+1.6%
SCALE Teens	12 to 17	Liraglutide, daily	251	56 weeks	4.64 percentage points lower than with placebo	Not given separately
STEP TEENS	12 to 17	Semaglutide, weekly	201	68 weeks	-16.1%	+0.6%

In the adolescent liraglutide trial, a reduction in BMI of at least 5% was observed in 51 of 113 participants in the liraglutide group and in 20 of 105 participants in the placebo group. By the trial’s own estimate, which allows for participants who dropped out, that is 43.3% against 18.7%. One in ten of the teenagers on the drug gave it up because of side effects: adverse events that led to discontinuation of the trial treatment occurred in 13 of them and in none on placebo.

Semaglutide did considerably more. A total of 201 participants underwent randomization, and 180 (90%) completed treatment. The mean change in BMI from baseline to week 68 was -16.1% with semaglutide and 0.6% with placebo. Nearly three in four of the treated teenagers lost at least 5% of their body weight.

The side effects followed the same pattern as in younger children. The incidence of gastrointestinal adverse events was greater with semaglutide than with placebo (62% vs. 42%). One finding was specific. Five participants (4%) in the semaglutide group and no participants in the placebo group had cholelithiasis, the medical term for gallstones, a known consequence of rapid weight loss.

An independent team in China pooled every placebo-controlled trial of the class in young people. Fourteen RCTs comprising 1349 participants were included, covering four different drugs. RCT stands for randomized controlled trial. Across them the drugs lowered weight and BMI, and gastrointestinal adverse events were more frequent in the GLP-1 receptor agonist group. Serious adverse events were no more common than with placebo. The pooled trials were short, and most of the participants were teenagers.

What happens when children stop an obesity drug

This is the question behind the WHO’s caution, and one trial gives a partial answer. In the adolescent liraglutide study, participants were followed for 26 weeks after their injections ended. After discontinuation, a greater increase in the BMI standard-deviation score was observed with liraglutide than with placebo. That score is a way of comparing a child’s BMI with others of the same age and sex. Put simply, the teenagers who had been on the drug regained ground faster once it was withdrawn.

Grummer-Strawn framed the same point as a question. The agency is particularly concerned about the youngest children, Grummer-Strawn said. Once a child is started very early on a drug of this kind, the question becomes: when does that stop?

A child who starts at six and needs the drug to hold its effect would be taking it through the whole of growth and puberty. No trial has followed children for anything like that long.

Where this fits: behavioral treatment for childhood obesity

The standard treatment for childhood obesity is not a drug. It is structured help for the family with eating, activity and habits, delivered over many hours.

In the United States, an independent panel reviewed the evidence in 2024. Approximately 19.7% of children and adolescents aged 2 to 19 years in the US have a body mass index (BMI) at or above the 95th percentile for age and sex, it noted. The 95th percentile means a BMI higher than 95% of children of the same age and sex on a reference chart. The chart is based on children measured decades ago, which is why far more than 5% of children today sit above that line.

The panel, the US Preventive Services Task Force (USPSTF), endorsed the behavioral route. The USPSTF recommends that clinicians provide or refer children and adolescents 6 years or older with a high BMI to comprehensive, intensive behavioral interventions. It judged the benefit of doing so to be moderate. Its recommendation did not extend to medicines.

So the WHO and the US panel arrive at similar places for younger children by different roads. Both put behavioral programs first. The WHO goes further and names an age below which it advises against drugs.

The drug trials do not conflict with that ordering. In all three, every participant received lifestyle support, and the medicine was tested as an addition to it.

What is not known about obesity drugs in children

The longest trial ran for 68 weeks. Nothing is known from randomized evidence about the effect of these drugs on growth, puberty, bone or the developing brain over several years.

The youngest group is barely studied. Eighty-two children took part in the only trial under 12, and 56 of them received the drug. A rare harm would not show up in a group that size.

Health outcomes have not been measured. The trials report BMI and weight. Whether treatment in childhood lowers the later risk of diabetes or heart disease, which is the reason for treating obesity at all, has not been tested.

Most of the evidence comes from one source. The three main trials were paid for by the company that sells the drugs. The pooled analysis was done by a separate team.

Which children would benefit most is unclear. The trials enrolled children with obesity by a BMI cutoff, without distinguishing those already developing complications from those who were not. Whether treatment suits a particular child is assessed by their doctor.

One year of a daily injection lowered body mass index in children aged 6 to 11 and a weekly one lowered it further in teenagers, with frequent gut side effects, in manufacturer-funded trials that stopped after little more than a year and, in the one that kept watching, showed BMI rising faster once treatment ended.