Stop Taking Semaglutide and Tirzepatide

Your skeleton is not static. It is constantly being demolished and rebuilt in a process that runs quietly in the background your entire life, and the balance between those two sides of the process is what determines whether your bones stay strong or slowly hollow out.

Researchers track that balance using 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 to replace what was lost. In a healthy skeleton, these two markers move roughly together. When one goes up, the other follows. When one slows down, so does the other. The ratio stays balanced, and net bone mass stays stable.

When you go on a calorie-restricted diet and lose weight, both markers slow down. Your body is doing less of everything, including bone remodeling, and that is completely normal. The balance stays intact even though the overall rate drops. Your bones are not being preferentially dismantled. They are just going through the same general metabolic slowdown as the rest of your tissue.

What researchers found in people taking semaglutide and tirzepatide does not look like that at all.

In a randomized, double-blinded trial published in eClinicalMedicine, people on semaglutide showed a 166.4 ng/L increase in CTX compared to placebo. Bone breakdown accelerated. But P1NP, the formation side of the equation, did not move. There was no compensatory increase. Bone was being dismantled faster than before, and the rebuilding side just sat there.

That pattern has a name. It is called uncoupled remodeling, which means the two sides of the process have come apart and are no longer tracking each other. Under normal conditions, the cells that break down bone and the cells that build new bone communicate constantly, and one signals the other to keep pace. When that communication breaks down, you get net bone loss even if both sides appear active, because one side is winning without a response from the other.

The same trial also measured bone mineral density at the hip and lumbar spine, and both decreased. That is the structural consequence of the uncoupling showing up in measurable bone loss at clinically significant sites.

Now here is where it gets more complicated, because the bone density number is not the only thing going wrong.

A large analysis of 73,483 matched patients per group presented at the American Academy of Orthopaedic Surgeons found that GLP-1 receptor agonist users had a 29% increased five-year osteoporosis risk compared to matched non-users, 4.1% versus 3.2%. That is the density problem. But the finding that stood out was a condition called osteomalacia, which is not the same thing as osteoporosis. Osteomalacia is a defect in bone mineralization, meaning the bone matrix is being laid down but it is not hardening properly. It is soft bone, not thin bone, and those are different problems. The relative risk increase for osteomalacia in GLP-1 users was 2.55, the highest of any musculoskeletal condition in the analysis.

Orthopedic surgeons have been reporting this independently, noting that bone in patients on these drugs feels softer than expected during procedures, and that anecdotal signal now has population-level data behind it.

So you have two separate things happening at the same time. You are losing bone mass through uncoupled remodeling, and the bone you still have is mineralizing incorrectly and becoming mechanically soft. Neither of those processes produces any symptoms until something breaks, and by then you have been building toward that break for months or years.

The surgery piece adds another layer. A 2025 AAOS study found that the standard three-to-five day pre-surgical hold on GLP-1 receptor agonists was insufficient because of how dramatically these drugs slow gastric emptying. The slowed emptying means stomach contents persist far longer than expected, and patients were aspirating under anesthesia. The recommendation moved to a fourteen-day discontinuation to normalize aspiration risk. That is not a pharmacokinetic footnote. That is surgeons observing a clinical problem serious enough to change pre-operative protocols.

The question of whether this is specific to semaglutide and tirzepatide, or whether it extends to all drugs in this class, matters because a newer compound called retatrutide has a different receptor profile. Semaglutide acts on one receptor. Tirzepatide acts on two. Retatrutide acts on three, and the third one is the glucagon receptor, which does something the others do not do.

The glucagon receptor tells the liver to pull stored fat and convert it into usable energy rapidly, driving production of something called beta-hydroxybutyrate, which is the primary ketone the body uses when it is running on fat rather than glucose. In the phase 2 retatrutide trial published in the New England Journal of Medicine, doses of 4mg and above produced measurable increases in beta-hydroxybutyrate, indicating that hepatic fat oxidation was actually being activated, not just suppressed food intake.

The theory, and it is still a theory based on published data rather than a confirmed mechanistic study, is that semaglutide and tirzepatide primarily work by reducing food intake and slowing gastric emptying, so the body experiences an energy deficit and responds accordingly, entering a conservation state that includes the uncoupled bone remodeling cascade. Retatrutide, by also activating the glucagon pathway, may shift where the energy comes from rather than just reducing how much comes in, which could mean the body never registers a true deficit and never triggers that conservation response.

That distinction matters because the bone loss signal on semaglutide and tirzepatide is not a minor side effect at the margin. It is a structural change to the organ system that holds your body together, and it accumulates silently over the entire duration of use.

The drugs change your weight. They do not change the fact that bone responds to energy deficit, and your skeleton does not care whether the deficit came from a restrictive diet or a receptor agonist.

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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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