Study to Evaluate Efficacy, Safety, and Tolerability of RGH-706 in Prader-Willi Syndrome

Age Limits: * In United States (USA), minimum age will be 17 years old. * In European Union (EU) countries, minimum age will be 18 years old. Inclusion Criteria: * Male or female patients aged ≥17 years in USA at screening or aged ≥18 years in EU at screening * Genetically confirmed diagnosis of PWS * HQ-CT total score ≥14 at screening * Body weight ≥40 kg/88 lbs and ≤200 kg/450 lbs * Stable body weight * Negative pregnancy test for females of childbearing potential and nonlactating at screening. * Patients must be able to provide or have a parent or guardian who is able to provide written informed consent and/or assent (as applicable) * Patients must have at least 1 consistent and reliable primary caregiver Exclusion Criteria: * Severe psychiatric disorders (eg, schizophrenia, bipolar disorder, or major depressive disorder), recent (within 6 months) * Risk of suicide according to the investigator's judgment * Uncontrollable diabetes mellitus or diabetes mellitus requiring insulin administration * Poorly controlled hypothyroidism or hyperthyroidism * Chronic or acute liver disease * History of bariatric surgery procedure * Uncontrolled obstructive sleep apnea. * History of malignancy within 5 years of screening * Systolic blood pressure (BP) ≥160 mmHg and/or diastolic BP ≥100 mmHg, pulse rate ≥100/min at screening. * Use of weight-lowering pharmacotherapy within 6 months prior to screening. * Known QT prolongation * Clinically relevant laboratory abnormalities * Any other condition that, in the investigator's opinion, might indicate that the patient is unsuitable for the study