This is a study of retatrutide in participants with obesity. The main purpose is to learn more about how retatrutide maintains body weight loss. The study will have two treatment phases: an 80 week lead-in phase in which all participants will take retatrutide dose 1 and a 36 week randomized, double-blinded phase in which participants will either take retatrutide dose 1, retatrutide dose 2, or switch to placebo. Participation in the study will last around 125 weeks.