Stop Taking Semaglutide and Tirzepatide
Your skeleton is not a fixed structure. It is a living tissue that is constantly being torn apart and rebuilt, and your body manages that process through a balance between two types of cells working in opposition to each other.
One type, called osteoclasts, breaks down old bone tissue. The other type, called osteoblasts, lays down new bone in its place. This cycle runs continuously throughout your life, and researchers can measure it in real time using two markers in the blood. The first is something called CTX, which tracks how fast bone is being broken down. The second is something called P1NP, which tracks how fast new bone is being formed. When these two markers move together, the system is balanced. When they split apart, something has gone wrong.
That split is exactly what researchers found in people taking semaglutide and tirzepatide.
Before getting into the drug data, it helps to understand what normal weight loss does to bone. When you eat less and lose body weight through caloric restriction alone, both CTX and P1NP slow down together. Bone turnover decreases across the board, but the ratio between breakdown and formation stays roughly intact. The architecture of the bone is preserved even if some density is gradually lost. This is expected and well-documented.
What the semaglutide data shows is categorically different.
In a randomized, double-blinded phase 2 trial published in eClinicalMedicine, researchers measured bone markers in adults on once-weekly semaglutide compared to placebo. CTX, the breakdown marker, increased by 166.4 nanograms per liter in the semaglutide group relative to placebo, and that difference was statistically significant. P1NP, the formation marker, did not move. There was no compensatory increase in bone building to match the accelerated breakdown. The researchers also measured actual bone density at the hip and lumbar spine and found decreases in both locations.
This pattern has a name. It is called uncoupled remodeling, which means the two sides of the bone cycle are no longer moving in sync. Osteoclasts are working harder, and osteoblasts are not responding. The result is a net loss of bone that is not accounted for by the weight loss itself.
The orthopedic surgery literature is picking up on something related but distinct. In a study of 73,483 matched patients per group presented at the American Academy of Orthopaedic Surgeons meeting in 2026, GLP-1 receptor agonist users had a 29 percent higher five-year risk of developing osteoporosis compared to matched controls, with rates of 4.1 percent versus 3.2 percent. But the finding that stood out was in osteomalacia, which is a condition where bone is not mineralizing correctly and becomes softer and more pliable than normal bone should be. The relative risk for osteomalacia in GLP-1 users was 2.55, meaning users were more than twice as likely to develop it. The absolute numbers were small, 0.2 percent versus 0.1 percent, but a doubling of risk in a condition that rarely appears at all is not something researchers dismiss easily.
Osteoporosis and osteomalacia are not the same problem. Osteoporosis is about losing bone mass. Osteomalacia is about the quality of the bone that remains. If both are happening simultaneously, the structural risk compounds in ways that a standard bone density scan may not fully capture, because density measurements do not tell you how well mineralized the bone actually is.
The surgical community has been paying attention to GLP-1 drugs for a separate and more immediate reason. These medications slow gastric emptying significantly, which means food and liquid remain in the stomach far longer than normal. When patients go under general anesthesia with an incompletely emptied stomach, the risk of aspirating stomach contents into the lungs increases. A study presented at the AAOS 2025 Annual Meeting found that the standard three to five day hold before surgery was not sufficient to normalize that risk and recommended a fourteen day discontinuation before total joint procedures to bring aspiration risk down to baseline. This is not about bone at all, but it reflects how broadly these drugs are altering physiology in ways the prescribing literature has not fully accounted for.
The mechanistic question is why. Why would a GLP-1 receptor agonist accelerate bone breakdown without triggering a matching formation response?
One line of thinking points to the energy signaling environment. When semaglutide or tirzepatide suppresses appetite and reduces food intake, the body eventually senses a caloric shortfall and begins mobilizing energy from storage. But the hormone signaling that normally tells the body it is adequately fueled may not fully recover between doses, and the bone remodeling system, which is energetically expensive to run, may be downregulated on the formation side as part of a broader conservation response while the breakdown side continues running independently.
Retatrutide, a newer compound currently in phase 2 trials, adds a third receptor target that semaglutide and tirzepatide do not activate: the glucagon receptor. The published phase 2 data in the New England Journal of Medicine showed that at doses of 4 milligrams and above, retatrutide produced measurable increases in beta-hydroxybutyrate, which is a ketone that indicates the liver is actively oxidizing stored fat for fuel. That signal means the body has access to energy from its own fat stores, not just from incoming food. If the body registers adequate energy availability even during a caloric deficit, the conservation response that may be driving uncoupled bone remodeling might not be triggered in the same way. This is theoretical at this point, and direct bone marker comparisons between retatrutide and semaglutide in controlled trials have not yet been published.
What is not theoretical is the uncoupled remodeling signal in the existing semaglutide data and the surgical observational findings in the orthopedic population. Both are pointing at something that standard prescribing guidance is not yet accounting for.
Bone loss is silent. There is no pain signal, no warning, and the changes accumulate over time in a way that only becomes visible after a fracture happens or a surgeon opens a joint and finds bone that does not behave the way it should. By the time the problem is obvious, years of drug exposure have already passed.
The real issue is that we are measuring these drugs by the weight they remove, when what actually matters is what gets removed along with it.
References
- 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
- 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%).
- 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.
- 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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