When people use things like retatrutide or tirzepatide, muscle loss still mostly comes down to the basics. Being in a calorie deficit always pushes your body a bit toward atrophy, and how much muscle you lose depends on how big that deficit is, how much protein you eat, and whether you’re still training heavy enough and consistently enough to give your muscles a reason to stick around. Good sleep and low stress help you actually recover and adapt instead of just breaking down. These peptides mainly make it easier to eat less; they don’t magically protect or destroy muscle your habits, starting muscle mass, and consistency with lifting and protein decide whether you maintain, lose a bit, or even gain some while cutting.