Last week I came across a post from a mom on X. She wrote that her daughter told her many of her teen friends were ordering weight loss injections they saw on TikTok. Some of these girls were 15, and most of what they were buying was gray market stuff sold straight to kids.

I haven't stopped thinking about it.

I shared my reaction on X here.

GLP 1 drugs are also being prescribed to teens by doctors. In December 2022 the FDA approved Wegovy (semaglutide) for weight management in kids 12 and older with obesity. For some teens, under a doctor's care, that may be the right call? My worry is what happens to a growing girl's body when her appetite is switched off during the years she's building her skeleton.

Here's what we know.

Girls build up to 90% of their peak bone mass by age 18. Boys get there by about 20. After that, bone mass keeps creeping up until the late 20s, and then the slow decline begins. Whatever she builds in her teens is what she lives on for the rest of her life.

And she needs estrogen to build it. Sex hormones are essential for bone development and girls who often miss periods sometimes have lower bone density.

I learned this the hard way. In my early 20s I had stress fractures constantly. I hadn't had a real period in years. And no, the bleed on birth control doesn't count. That's a withdrawal bleed from the pill, not a real period. The synthetic estrogen in the pill also doesn't protect your bones the way your own cycle does. Studies show teen girls on the pill build less bone than girls who aren't on it.

I've been strength training consistently (ie. lifting HEAVY) to reverse the damage. I believe if I hadn't, I'd probably be on track to have osteoporosis.

Now imagine a teen girl on an appetite suppressant. She might be eating 1000-1400 calories a day. She's still growing. She's going to school and maybe playing a sport. Her body senses less food coming in and to her brain that looks like a famine.

So her body starts saving energy wherever it can, and her period is one of the first things to go. Her brain stops sending the signal her ovaries need. Her estrogen falls. Her cycle gets irregular, and then it stops. This is called hypothalamic amenorrhea. Athletes who don't eat enough for their training get it too.

So she loses her period and bone building capacity at the exact age she can LEAST afford it. You can improve bone later in life, but you can't fully reopen that teenage window.

What about GLP 1s specifically? Honestly, we don't have long term data on teen bones yet. Weight loss in general tends to be hard on bone, and there is a NIH funded study being done on bone health in 12-21 year olds starting these drugs. Novo Nordisk's own trial in kids and teens is also measuring bone density. So the research will take some time to catch up. But to me it is obvious that this can't be good.

That's why I keep saying a regular cycle is a vital sign. A cycle that comes every 24-35 days tells you the body feels safe and fed. A missing period is a message that is never worth ignoring.

If you have a teen daughter, here's what I'd watch.

Is she getting her period regularly?

Is she eating meals with enough protein, calcium and overall food?

Is she using anything to curb her appetite, prescribed or not?

And if she is on a GLP 1 from her doctor, ask how her cycle, nutrition and bone health will be tracked.

If your own period has gone out the window, the same rules apply to you. My free guide walks through the first steps to get it back: getyourperiodback.joinferta.com.

And if you want help finding the root cause of your missing or irregular cycle, we work with women 1:1. You can apply at joinferta.com.

More soon,

Preethi