GLP-1s for Teenagers

I want to be careful with this one, because it is the topic where the loudest opinions have the least clinical contact, and because the person actually affected is usually not the person asking.

What the evidence says

STEP TEENS, published in the NEJM in 2022, randomised adolescents aged 12 to under 18 with obesity to once-weekly semaglutide 2.4 mg or placebo, alongside lifestyle intervention, over 68 weeks. The mean reduction in body mass index was substantially greater than placebo — proportionally larger than the adult result in STEP 1 — with improvements in cardiometabolic measures. Side effects were dominated by gastrointestinal symptoms, as in adults.

An earlier trial of liraglutide in adolescents had reported benefit on a smaller scale. Semaglutide marketed as Wegovy now carries an indication from age 12.

The 2023 American Academy of Pediatrics guideline also shifted the framing: it recommends offering pharmacotherapy alongside intensive health behaviour and lifestyle treatment in appropriate adolescents, rather than reserving it until years of lifestyle intervention have failed. That recommendation was controversial and the reasoning is worth understanding — adolescent obesity rarely resolves on its own, and delay has costs of its own.

What the argument is usually actually about

Most conversations I have with parents are not really about the trial data. They are about whether treating this with a drug means giving up, whether it means the child is broken, and whether it is the parent’s fault.

I would say the same thing here as I say in the room. Obesity in adolescence is a biologically defended state with strong heritable components, and it very seldom resolves spontaneously. Treating it is not a verdict on anyone’s parenting, and declining to treat it is not neutral — it is a decision with its own consequences, in a body and in a life.

That is not an argument that every eligible teenager should take one. It is an argument for making the decision on the merits rather than on shame.

Where I am genuinely cautious

Nutrition in a growing body. This is my main concern and it is under-discussed. An adolescent is still laying down bone mass — roughly 90% of peak bone mass accrues by age 18–20 — and still building muscle. Halve the food intake without attention and you take calcium, vitamin D, iron, and protein down with it.

So the requirements are stricter than for adults, not looser:

• Protein at the upper end of the range, spread across meals
• Calcium and vitamin D actively attended to, because this window does not come back — the reasoning is in the bone health rankings
• Iron, particularly in menstruating adolescents
• Resistance training, which builds both muscle and bone during the years when it matters most

The general framework in muscle is the whole game applies with more urgency here, because a deficit accrued at 15 is not simply recoverable at 25.

Eating disorders. Adolescence is when restrictive eating disorders most commonly begin, and these drugs produce exactly what those disorders reward: very low intake, rapid loss, indifference to food. Screening before treatment and monitoring during it are not optional at this age, and this is the part most often skipped in a hurried appointment. The broader discussion is in food noise, mood, and the quiet months.

Duration. If obesity is a chronic condition and these are long-term treatments, starting at 13 raises a question nobody can answer: what does continuous exposure from adolescence into middle age look like? The honest answer is that nobody knows, because the drugs have not existed that long. That uncertainty is set out in what we know about long-term safety, and it weighs differently at 13 than at 53.

Contraception. Adolescents who could become pregnant need this discussed properly. These drugs are not for use in pregnancy, fertility can increase as weight falls, and tirzepatide reduces oral contraceptive effectiveness for 4 weeks after starting and after each dose increase — the detail is in GLP-1s and your other medications.

What good care looks like at this age

• Prescribing by, or in partnership with, a clinician experienced in adolescent obesity — not a telehealth form
• Intensive lifestyle support alongside, not replaced by, the medication
• A written protein target and a resistance training plan from week one
• Baseline and periodic vitamin D, B12, ferritin, and a growth chart that keeps being plotted
• Eating disorder screening at the start and at intervals
• The adolescent in the conversation, not just spoken about
• An explicit plan for what happens at 18, and for what happens if treatment stops

That last one matters. Weight regain after discontinuation is well documented in adults, and there is no reason to expect adolescents to be exempt — what happens when you stop.

The thing I would say to a parent

The question is not whether it would be better if your child did not need a medication. Of course it would. The question is what happens across the next decade in each of the two available futures, and that comparison has to be made honestly rather than through the assumption that doing nothing is the safe option.

Then, if you proceed, the work is nutritional and behavioural and it does not stop because a prescription started. The drug handles appetite. It has no opinion about whether your child gets enough protein, enough calcium, or enough sleep — and at this age those are not optimisations. They are the growing.