This research study is comparing the effectiveness of a weight loss medication called Tirzepatide in young adults with Prader-Willi Syndrome and/or hypothalamic obesity, as compared to young adults with obesity that is unrelated to a genetic syndrome or underlying medical cause. These groups will be given medication for 1 year to see how weight and other health factors are effected by the medication.

This study is for the following individuals: * Age 18-26. * Have Prader-Willi Syndrome, Hypothalamic Obesity, or Obesity unrelated to a genetic syndrome or medical condition. * Have a BMI in the obesity range If you/your child decide to take part in the research study, you/your child would participate in the study for approximately 56-60 weeks. During this time the following can be expected: * Receive tirzepatide for once-weekly dosing. * Complete 6 in-person SCH study visits * Complete 4 telehealth visits. * Complete the following research procedures: * Medical Record Review * Vital Signs * Anthropometry (e.g., height, weight, waist measurements) * Physical Exams * Laboratory Tests (e.g., fasting blood draws, urine test) * Dual-Energy Absorptiometry (DXA) scans * Questionnaires