This has become the question I get asked more than almost any other, and it usually arrives in some version of the same sentence. My doctor just recommended Wegovy, and I already have osteopenia, so is this going to wreck my bones?
I want to be straight with you about the state of the evidence before I say anything else. It's thin, and it doesn't all point the same way. The large fracture studies look reassuring, the smaller bone density studies do not, and none of them were done in the people most likely to be reading this. The question isn't settled, and I'm not going to pretend otherwise.
Here is where I land anyway. We have no evidence these drugs poison bone. What we do have is good evidence that losing a lot of weight quickly costs you bone, and these drugs are very good at producing exactly that kind of weight loss. Almost all of the real risk sits there, and most of it is manageable.
I'm not making a case against these drugs. For many people the gains to blood sugar and to the heart are large. If you plan to take one and your bones are already thin, a few things are worth doing alongside it.
What These Medications Are
GLP-1 stands for glucagon-like peptide-1, a hormone your gut releases after you eat. It nudges insulin up, slows how fast your stomach empties, and tells your brain you have had enough. These drugs copy that hormone and last far longer in the body. Semaglutide is sold as Ozempic and Wegovy, tirzepatide as Mounjaro and Zepbound, and liraglutide as Victoza and Saxenda.
All were built for diabetes, and the weight loss became the headline. People on weekly semaglutide lost about 34 pounds over sixteen months, against roughly 6 pounds on placebo (Wilding and colleagues, New England Journal of Medicine, 2021). Tirzepatide has produced drops of more than a fifth of body weight (Look and colleagues, Diabetes, Obesity and Metabolism, 2025). Your skeleton notices a change that big.
What the Evidence Actually Shows
The calming headline comes from a study of 133,606 older adults who all had type 2 diabetes, comparing those who started a GLP-1 against those who started a different diabetes pill. The GLP-1 group broke fewer bones, about one fracture avoided for every 126 people treated over three years. But the authors said plainly that the finding should not be stretched to people who already have osteoporosis or a broken bone behind them (Hamad and colleagues, JAMA Network Open, 2026). That's most of the people reading this. Tucked inside the same paper is a look at people without diabetes, where GLP-1 use was tied to a 13% higher fracture rate instead.
The work done in people more like my readers measured bone density rather than fractures, and it went the other way. A Danish team gave semaglutide or placebo for a year to 64 adults whose bones were already thin and who did not have diabetes, most of them women, average age 63. The semaglutide group lost about 9% of their body weight, and their bone density fell 2.6% at the hip compared with placebo (Hansen and colleagues, eClinicalMedicine, 2024). Your bones are always being torn down and rebuilt, and blood tests showed the tearing-down speeding up while the rebuilding stayed flat. It's a small trial, and it can't separate what the drug did from what the weight loss did. Still, the direction it points is down.
There's one finding I'm not going to bury. In a large heart trial, hip and pelvic fractures showed up in 1.0% of the women on semaglutide against 0.2% on placebo, and the gap was wider still in people over 75 (Paccou and colleagues, Journal of Bone and Mineral Research, 2025). That's a five-fold difference and it deserves saying out loud. I would not treat it as proven either. These were side effects counted after the fact rather than fractures the trial set out to track, the number of cases was small, and no other trial has seen the same thing.
That's the mixed picture I mentioned at the top. Good-looking fracture data from a group unlike yours, falling bone density in a group like yours, and a pooled look at 38 trials that could not settle it either (Karam and colleagues, Osteoporosis International, 2025).
The Weight Loss Is the Part I Worry About
Losing weight quickly lowers bone density no matter how you do it. That has been seen for decades in people dieting with no drug at all, and the bone experts who reviewed the GLP-1 studies found that what these drugs do to the skeleton looks like what plain eating less does (Liu and colleagues, Bone Research, 2025). Part of the reason is physical. Bone is built to the load it carries, and hauling eighty fewer pounds up the stairs is less load. Eating far less of everything also means less calcium and protein coming in.
Here is what I think the real difference is. When you lose weight by eating less and moving more, the moving-more half guards your bones while the eating-less half wears them down. These drugs take away your appetite. They do not put a barbell in your hands. You can lose forty pounds without ever loading your skeleton once, and that is the kind of weight loss your bones handle worst.
Muscle goes with the fat, which makes it worse. In scans done alongside the semaglutide trials, about a quarter of the tissue lost was muscle (Wilding and colleagues, Journal of the Endocrine Society, 2021). Weaker legs mean worse balance, and almost every fracture that matters happens because somebody fell over.
What Actually Protects Your Bones
The most useful study here isn't about the drugs at all. It's about what you do while you take them. Danish researchers put 195 adults with obesity into one of four groups for a year: exercise alone, liraglutide alone, both together, or neither (Jensen and colleagues, JAMA Network Open, 2024). The pattern was clean.
- Liraglutide alone. Lost about 30 pounds. Bone density dropped at both the hip and the spine.
- Exercise alone. Lost about 25 pounds. Bone density held.
- Both together. Lost about 37 pounds, more than any other group, and bone density at the hip, spine, and forearm ended up no different from the group that had barely lost weight at all.
Read that third line again. The group that lost the most weight kept its bone, because exercise was part of the deal. The exercise wasn't brutal either, about two hours a week, hard enough to feel but nothing like an athlete's schedule.
Those people were 18 to 65 and otherwise healthy, so nobody has shown this yet in a woman of 75 with full osteoporosis. The type seems to matter too. In a separate program, hip bone density fell 0.7% among people lifting weights against 2.6% among those doing aerobic work. If you have to pick one, pick the one with weight in your hands.
What I Would Do
None of this is a reason to turn down a drug your doctor thinks you need. It's a reason to do a few things alongside it.
Get a baseline bone density scan. Ask for one if you are past menopause, over 65, have a family history of hip fracture, or have broken a bone as an adult, and know your starting numbers before you lose thirty pounds rather than after. Without a baseline, a scan two years from now tells you little.
Lift something heavy, twice a week at least. This is the highest-value item on the list, and the evidence for it beats anything else I could suggest. Resistance work, not only walking. My posts on weight-bearing versus resistance exercise and balance training cover it.
Protect your protein, calcium, and vitamin D. These drugs make food less appealing, so the calories you do eat need to be worth something. Gaps are easy to drift into when you are barely hungry. My post on protein and calcium has the targets, and vitamin D and bone health covers the rest.
Ask about repeating the scan at a year. The usual two to three year gap was worked out for people whose weight was steady. One bone expert has argued that older patients losing around 9% of their weight should be rechecked at twelve months (Ambrogini, Journal of Bone and Mineral Research, 2026). That is her judgment rather than a guideline, and I agree with it.
Questions Worth Bringing to Your Appointment
- Should I have a bone density scan before I start, or early on?
- How fast do we expect me to lose weight, and can we slow that down?
- What protein target should I aim for while my appetite is low?
- If I already have osteopenia or osteoporosis, does that change what you advise?
- When would you want to repeat my scan, and what result would make us change course?
Where This Leaves Us
I can't tell you these drugs are bad for bone, because the evidence doesn't say that. I also can't tell you your skeleton is safe on them, because the study that would show it has not been done.
What the evidence does support is narrower, and it is the part you control. Big weight loss lowers bone density, these drugs produce it reliably, and many people now get there without the physical work that used to come bundled with getting smaller. The drug isn't the thing to fear. Losing weight while sitting still is.
Ask me again in a few years and I may have to revise this. Nobody has published bone density results for tirzepatide yet, so anyone claiming to know what that drug does to your skeleton is guessing. I'll update this post when better evidence arrives.
If you are weighing a bone drug alongside all of this, my posts on bisphosphonates and bone-building injections cover the ones that treat osteoporosis directly.