Weight-loss injections like Ozempic, Wegovy and Mounjaro have quickly become some of the most widely used tools for rapid fat loss. But alongside their popularity, Canadian researchers are now raising concerns about a troubling new side effect. While many users expected issues such as hair thinning, digestive discomfort or skin sagging, experts say the real risk may be far more serious. These medications work by targeting appetite receptors in the brain, reducing hunger and helping users eat significantly less. Although Ozempic was originally designed for Type 2 Diabetes, the drug has become a go-to option for shedding pounds fast. However, new research suggests the physical cost of this weight loss may be much higher than anticipated.
According to a review by Canadian researchers working with Les Mills and UKactive, people taking these medications could experience a loss of lean body mass comparable to ten years of aging. With an estimated 2.5 million users in the UK alone, the findings are raising nationwide concern. Middle-aged and older adults may be particularly vulnerable, as natural age-related muscle loss combined with drug-induced decline could significantly increase frailty. The report warns this reduction in muscle and bone mass heightens the risk of injury, falls and long-term mobility issues—especially for users who do not incorporate strength training into their routine.
Lead researcher Dr. Gillian Hatfield explained that participants who exercised 150 minutes per week while reducing weekly calorie intake by 500 still lost around 11% of their lean mass. She compared the magnitude of this muscle loss to the effects of bariatric surgery, cancer treatments, or a full decade of biological aging. Fitness experts, including Les Mills’ head of research Bryce Hastings, emphasize the importance of regular resistance training for anyone taking weight-loss drugs, though they acknowledge more studies are needed to fully understand the impact.
Manufacturers have responded cautiously to the findings. Novo Nordisk, which produces Ozempic and Wegovy, advises users to take the medications only as prescribed and under medical supervision, noting their clinical trials did not specifically study muscle-mass changes. Eli Lilly, maker of Mounjaro, reiterated that patient safety remains its priority and encouraged users to maintain balanced nutrition, physical activity, and open communication with healthcare providers. As demand for weight-loss injections grows, experts agree on one message: rapid fat loss must be balanced with long-term muscle health to avoid unintended consequences.
