Semaglutide has become one of the biggest success stories in obesity treatment, helping many patients lose 15 percent to 20 percent of their body weight. But new research suggests the celebrated weight-loss drug may come with an overlooked trade-off, at least in mice, by temporarily weakening bones even more than dieting alone.
The study, published in the latest issue of Bone by Cell Press, found that obese mice treated with semaglutide developed lighter, weaker thigh bones than mice that lost the same amount of weight simply by eating fewer calories. The findings suggest the drug’s effects on bone may not be explained by weight loss alone.
Researchers from the University of Guelph in Canada found that semaglutide reduced both fat and lean muscle, while also lowering the activity of osteoblasts, the specialized cells responsible for building new bone. As a result, the mice’s femurs became less dense, less stiff and less able to withstand stress.
The good news is that the effect did not appear permanent.
Six weeks after semaglutide treatment stopped, the mice’s bone weight, strength and stiffness had recovered to levels comparable to untreated animals, suggesting the changes depended on continued exposure to the drug rather than causing lasting damage.
The findings add another piece to the rapidly evolving picture of GLP-1 receptor agonists, the class of medicines that includes semaglutide. While these drugs have transformed obesity care by helping patients lose substantial weight through reduced appetite and food intake, researchers have increasingly turned their attention to what happens to the rest of the body as the kilos disappear.
Weight loss itself is known to reduce bone density because lighter bodies place less mechanical load on the skeleton. What surprised the researchers was that semaglutide appeared to have a greater impact on bone strength than calorie restriction that produced an equivalent amount of weight loss.
The researchers cautioned against drawing conclusions for people. The study involved only obese laboratory mice, and human bones do not necessarily respond the same way.
Instead, they say the findings underscore the need for clinical studies to determine whether people taking semaglutide, particularly for extended periods, should also monitor bone health alongside the shrinking number on the weighing scale.
