Stop Taking Semaglutide and Tirzepatide

Your skeleton is not static. It is a living tissue that gets demolished and rebuilt on a continuous cycle, and your body manages that cycle through two competing processes running at the same time.

The demolition side uses cells called osteoclasts, which break down old or damaged bone tissue so it can be cleared away. The construction side uses cells called osteoblasts, which lay down new mineral matrix to replace what was removed. Researchers can track both sides of this process using blood markers: something called CTX, which measures the byproducts of bone being broken down, and something called P1NP, which measures the proteins your body produces when it is actively building new bone. When CTX goes up, breakdown is accelerating. When P1NP goes up, formation is accelerating. The health of your skeleton over time depends entirely on whether those two signals stay in balance.

That balance is what makes the semaglutide and tirzepatide data worth paying close attention to.

When you lose weight through calorie restriction alone, both markers slow down together. CTX drops because your body is not cycling bone tissue as aggressively, and P1NP drops for the same reason. The ratio between them stays roughly intact, which means even though the overall pace of remodeling slows, you are not losing ground. The construction crew shrinks, but so does the demolition crew. This is considered a normal and expected adaptation to weight loss, and it has been documented consistently across diet studies.

What researchers found in people taking semaglutide told a different story.

In a randomized, double-blinded phase 2 trial published in eClinicalMedicine, researchers measured both markers in adults on once-weekly semaglutide compared to placebo. CTX increased by 166.4 nanograms per liter in the semaglutide group relative to placebo, and that difference was statistically significant. P1NP did not move. Bone breakdown accelerated while bone formation stayed flat, and that gap between them is something called uncoupled remodeling, which is when the demolition crew shows up but the construction crew does not follow. The same trial also found decreased bone mineral density at both the hip and lumbar spine in the semaglutide group.

This is not what you would expect to see from weight loss alone. The pattern is different in a meaningful way because in normal calorie restriction, both markers move together. Here, one moved and the other did not, which suggests the drug is driving the resorption signal through a mechanism that is separate from the weight loss itself.

The orthopedic surgery community has been arriving at a similar concern from a completely different direction.

At the American Academy of Orthopaedic Surgeons annual meeting in 2026, researchers presented findings from a matched cohort of over 73,000 patients per group comparing GLP-1 receptor agonist users to non-users. Over a five-year follow-up period, GLP-1 users had a 29 percent higher rate of osteoporosis diagnosis, translating to 4.1 percent of patients versus 3.2 percent in the control group. But the number that stands out more is the osteomalacia finding. Osteomalacia is a condition where bone fails to mineralize properly, meaning the structural scaffold of the bone exists but it is not hardening the way it should, leaving bone that is softer and more pliable than normal. In this dataset, osteomalacia showed the greatest relative risk increase of any musculoskeletal outcome, with a relative risk of 2.55 compared to controls.

These surgeons were not looking at blood markers in a lab. They were looking at what they found when they opened joints during surgery, and what they found was bone that was behaving differently than expected given the patient's age and weight history.

So you have two separate signals pointing at the same problem. The blood marker data shows that bone breakdown is outpacing formation. The surgical data shows that the bone which does remain is not mineralizing correctly. Those are two distinct problems that can coexist and compound each other, and neither one produces symptoms you would notice day to day. You will not feel your CTX rising. You will not feel bone softening. The first signal most people would get is a fracture that happens more easily than it should have.

The pre-surgical protocol change is worth understanding in its own right. The same orthopedic community that is flagging bone quality concerns has also pushed for a 14-day discontinuation window before total joint replacement surgery, not because of the bone issue but because semaglutide and tirzepatide slow gastric emptying significantly enough that patients are arriving for surgery with food still in their stomachs hours after fasting, and aspirating stomach contents under general anesthesia. A shorter 3 to 5 day hold was found to be insufficient to normalize that risk. The 14-day window was what it took to bring aspiration pneumonitis risk back to baseline.

Now the question of whether this bone remodeling pattern shows up with retatrutide is worth examining because the mechanism of the drug is genuinely different.

Retatrutide is a triple agonist, meaning it activates three receptor pathways simultaneously: GLP-1, GIP, and glucagon. The glucagon component is what semaglutide and tirzepatide do not carry. Glucagon receptor activation tells the liver to rapidly convert stored fat into usable energy through a process called hepatic fat oxidation, and in the phase 2 trial published in the New England Journal of Medicine, retatrutide produced measurable increases in beta-hydroxybutyrate at doses of 4 milligrams and above, which is a direct marker of that fat oxidation process running at an elevated rate.

The theory is that this matters for bone because the uncoupled remodeling seen with semaglutide may be tied to how the body reads its own energy state. When caloric intake drops sharply and the body detects a large sustained deficit, it can enter what might be called conservation mode, where non-immediate resources get redirected and signals that maintain bone turnover balance get disrupted. If the glucagon agonist in retatrutide keeps the liver converting stored fat fast enough that the body never registers a true deficit at the cellular level, the conservation cascade that may be driving the uncoupled remodeling in semaglutide users might never get triggered.

This remains a theory. There are no long-term randomized trials on retatrutide bone markers published yet, and the glucagon-bone connection is still being worked out mechanistically. But the logic is grounded in real pharmacology and the contrast between the drug classes is real.

The deeper takeaway here is about what the body counts as starvation. Semaglutide and tirzepatide reduce how much food comes in without replacing that energy from anywhere else, and the body has been wired for millions of years to treat a large sustained caloric gap as a threat worth defending against. Bone is metabolically expensive to maintain and represents a mineral reservoir the body can access. If the drug is pulling on one end of a very old biological tripwire, the skeleton pays a cost that no one can see or feel until it becomes a structural problem.

That is not a reason to make any clinical decision on your own. But it is a reason to ask your doctor about baseline bone marker testing before starting these medications, to get those markers tracked longitudinally while on them, and to understand that the weight loss you can see on a scale may be coming with changes underneath it that the scale will never show you.

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References

1. Hansen MS, Wolfel EM, Jeromdesella S, et al. 2024. Once-weekly semaglutide versus placebo in adults with increased fracture risk: a randomised, double-blinded, two-centre, phase 2 trial. eClinicalMedicine The Lancet. Finding: Semaglutide increased bone resorption marker CTX by 166.4 ng/L vs placebo p=0.021 with no compensatory increase in bone formation marker P1NP, demonstrating uncoupled bone remodeling. Also decreased areal BMD at hip and lumbar spine. Source
2. Wajahath M, et al. (2026). GLP-1 Receptor Agonist Use and Long-Term Musculoskeletal Health. Presented at American Academy of Orthopaedic Surgeons (AAOS) Annual Meeting, March 2-6, 2026, New Orleans. Finding: In 73,483 matched patients per group, GLP-1 RA users had 29% increased 5-year osteoporosis risk (4.1% vs 3.2%) and osteomalacia showed the greatest relative risk increase (RR 2.55, 0.2% vs 0.1%).
3. AAOS 2025 Annual Meeting. New Study Recommends Stopping GLP-1 Agonists 14 Days Before Total Joint Arthroplasty to Reduce Anesthesia Risks. Finding: 3-5 day hold was insufficient; 14-day discontinuation normalized aspiration pneumonitis risk under anesthesia due to GLP-1-mediated delayed gastric emptying.
4. Jastreboff AM, Kaplan LM, Frias JP, et al. 2023. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. Finding: Retatrutide produced dose-dependent weight loss with beta-hydroxybutyrate increases at 4mg+ doses indicating glucagon-driven hepatic fat oxidation. Source

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