The purpose of this study is to evaluate the efficacy and safety of retatrutide in participants who have obesity or overweight (J1I-MC-GZBJ master protocol) including subsets of participants who have knee osteoarthritis (OA) (J1I-MC-GOA1) or who have obstructive sleep apnea (OSA) (J1I-MC-GSA1). This study will last about 89 weeks and will include up to 24 visits.