Stop Taking Semaglutide and Tirzepatide

Your skeleton is not static. It is constantly being dismantled and rebuilt in a process that runs every single day of your life, and the balance between those two sides of the process is what determines whether your bones are getting stronger or quietly falling apart.

Researchers track this balance with two markers in the blood. The first is something called CTX, which measures how fast your body is breaking down old bone tissue. The second is something called P1NP, which measures how fast your body is laying down new bone. When those two move together, your skeleton stays intact. When they move apart, you have a problem.

Understanding why these two markers matter starts with understanding the system they measure.

Bone remodeling works like a renovation crew where one team tears out the old material and a second team comes in right behind to pour the new foundation. The tear-down team is made of cells called osteoclasts and the build team is made of cells called osteoblasts, and under normal conditions these two crews are tightly coupled to each other, meaning wherever one goes, the other follows. The ratio stays balanced and your net bone density stays stable.

Now here is what happens when you simply eat less food and lose weight. Both teams slow down together. CTX drops because your body is in a lower metabolic state and there is less tissue turnover happening overall, and P1NP drops along with it at roughly the same rate. The balance holds. Bone density may change modestly during a diet, but the remodeling process itself is not broken. This is completely expected physiology.

What researchers found with semaglutide breaks from that pattern entirely.

In a randomized, double-blinded trial published in eClinicalMedicine, people on once-weekly semaglutide showed a 166.4 nanogram per liter increase in CTX compared to placebo. The tear-down crew accelerated. But P1NP, the marker for new bone formation, did not move to compensate. The build team stayed flat while the demolition kept going, and this is what researchers call uncoupled remodeling, which means the two sides of the process have come apart from each other.

That decoupling matters because it means the deficit is not being repaired. Every cycle of bone breakdown that runs without a matching cycle of bone formation leaves you with slightly less structural material than you had before, and because you cannot feel bone density changing, there is no signal telling you this is happening.

The same large-scale data from orthopedic research confirms the downstream consequence. Across 73,483 matched patients per group, people using GLP-1 receptor agonists had a 29 percent higher five-year risk of osteoporosis compared to matched controls who were not on these drugs, which translated to a rate of 4.1 percent versus 3.2 percent. That is a meaningful difference in a patient population where fracture risk carries serious consequences.

But there was a second finding in that data that is more striking. Osteomalacia, which is a condition where bone loses its mineral density and becomes physically softer rather than just thinner, showed a relative risk increase of 2.55 in GLP-1 users compared to controls. This is a separate problem from osteoporosis. Osteoporosis means you have less bone. Osteomalacia means the bone you do have is not properly mineralized, so it is structurally weak in a different way. When orthopedic surgeons began reporting independently that bone in patients on these drugs felt softer than expected during procedures, they were describing something consistent with this mineralization failure.

So you have two separate problems happening simultaneously and compounding. Less bone being formed, and the bone that remains being inadequately mineralized. Neither of these produces symptoms you would notice until something breaks.

The surgical community has registered this concern in a practical way. Research presented at the American Academy of Orthopaedic Surgeons established that a three to five day hold before surgery was not sufficient to normalize aspiration risk, and that patients needed to stop these medications at least 14 days before total joint procedures. The reason is that semaglutide and tirzepatide slow gastric emptying dramatically enough that food and liquid remain in the stomach far longer than normal, which creates the risk that a patient under general anesthesia aspirates stomach contents into their lungs. The 14-day figure was the threshold at which aspiration pneumonitis risk returned to normal. That is how profoundly these drugs are altering the physiology of the gastrointestinal system.

Now, the question that follows is whether tirzepatide, which adds a GIP receptor agonist to the GLP-1 mechanism, shows the same pattern, and from the available data the answer appears to be yes, at least in terms of the bone remodeling signal, because the mechanism driving the uncoupling seems to be downstream of both.

The mechanism that may be driving the uncoupled remodeling in semaglutide and tirzepatide is still being worked out, but the leading candidate is that these drugs suppress appetite enough to create a significant energy deficit, and that energy deficit triggers something called conservation mode, where the body begins prioritizing survival functions over bone maintenance. Bone remodeling is metabolically expensive, and when the body senses it is not getting enough incoming energy, it begins pulling back on the build side of the process while the breakdown side continues at its normal rate or accelerates to liberate stored minerals.

Retatrutide works differently because it adds a third receptor target, the glucagon receptor, that the other two drugs do not have. What the glucagon agonist activity does is tell the liver to mobilize stored body fat and convert it into usable fuel through a process called hepatic fat oxidation. The evidence for this comes from the phase two trial published in the New England Journal of Medicine, where patients on retatrutide doses of 4 milligrams and above showed measurable increases in beta-hydroxybutyrate, which is a marker of fat being burned for fuel rather than glucose. When the liver is generating that much energy from stored fat, the body's energy sensing system does not register a deficit the same way, and the signal that triggers conservation mode and the downstream bone breakdown cascade may never get sent.

The theory, stated plainly, is that semaglutide and tirzepatide take food energy away from the body without fully replacing where that energy comes from, and the body responds the way it always has to energy scarcity: it starts cannibalizing structural tissue. Retatrutide appears to replace the energy source at the same time it reduces appetite, which may be why the bone remodeling markers stay balanced.

This is still a theory grounded in early data and not a proven clinical conclusion. But the signal across an orthopedic database of over 140,000 patients, a randomized controlled trial showing a 166 nanogram per liter uncoupled shift in bone markers, and independent surgical observation of bone quality is coherent enough to take seriously.

The bone you have now is the foundation every other health outcome builds on, and it is being remodeled silently every day regardless of what you take or do not take.

---

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

---

Join the free community:
Men: Iron Forge Brotherhood
Women: Powerhouse Fitness