Evidence-graded answer
Can I build muscle on a GLP-1?
Yes — with deliberate resistance training and adequate protein. Without it, 25-40% of weight lost on GLP-1 comes from lean muscle. Lifting 2-3x/week + 1.2-1.6 g/kg ideal-body-weight protein preserves and can grow muscle while losing fat.
The catabolic risk on rapid weight loss is muscle loss — same problem as with any aggressive caloric deficit, not GLP-1-specific.
Protocol: 2-3 resistance training sessions per week hitting all major muscle groups, progressive overload, protein at 1.2-1.6 g/kg IBW.
Reduced appetite makes hitting protein targets harder — protein shakes, Greek yogurt, cottage cheese, and lean meat-forward meals are practical.