GLP-1 receptor agonists like semaglutide and tirzepatide cause weight loss that's 20-30% lean muscle mass, not just fat tissue. This muscle loss becomes particularly concerning during cancer treatment, where low skeletal muscle mass correlates with higher rates of severe toxicity, more treatment dose modifications, and worse survival outcomes. The drugs also delay gastric emptying, potentially altering absorption of oral cancer medications. This analysis exposes a critical blind spot in the widespread prescribing of GLP-1 agonists. While these medications offer legitimate cardiometabolic benefits, their muscle-wasting effects could inadvertently compromise cancer treatment outcomes precisely when patients need maximum physiological reserves. Cancer patients already face treatment-related muscle loss and nutritional challenges, making additional lean mass reduction potentially devastating. The commentary advocates for systematic body composition monitoring, resistance exercise protocols, and dietetic support before continuing these medications during active cancer therapy. This represents an important paradigm shift from viewing GLP-1 agonists as universally beneficial weight-loss tools to recognizing their complex tissue-specific effects that require careful clinical consideration in vulnerable populations.