While the drugs certainly contribute to weight loss and health gains, they also cause a decline in muscle that some doctors find concerning. In trials of Wegovy, up to 40% of weight loss was from a decrease in lean or fat-free mass, rather than excess fat. In addition, quitting the drugs can mean adding back the pounds.

Those who take tirzepatide, the drug sold as Zepbound and Mounjaro, could lose more weight than those who take semaglutide, known as Ozempic and Wegovy, according to new research.