A Study to Assess the Long-Term Safety of Pharmaceutical Grade Synthetic Cannabidiol Oral Solution in Participants With Prader-Willi Syndrome

Inclusion Criteria: 1. Completed activities up to and including Visit 10 (Study Completion) of INS011-16- 085. 2. Participant and/or parent(s)/caregiver(s) fully comprehend the informed consent form and assent form, understand all study procedures, and can communicate satisfactorily with the investigator and study coordinator, in accordance with applicable laws, regulations, and local requirements. 3. If female, is either not of childbearing potential or practicing medically acceptable methods of birth control. 4. Psychotropic treatment will be permitted if the participant has been on a stable dose during the INS011-16-085 and does not anticipate a dose change during the course of the study. 5. Growth hormone treatment will be permitted if the participant has been on a stable dose during INS01-16-085. 6. Any other treatment including thyroid hormones should be stable prior to entering the INS011-17-115 study. 7. In the opinion of the investigator, the parent(s)/caregiver(s) is (are) willing and able to comply with the study procedures and visit schedules, including venipuncture, and the visit schedules. Exclusion Criteria: 1. Participant or parent(s)/caregiver(s) have commitments during the study duration that would interfere with attending all study visits. 2. Experienced an anoxic episode related to study drug requiring resuscitation during the previous study. 3. Uncontrolled Type I and Type II Diabetes. 4. Developed an adverse event thought to be related to CBD in the previous study and the investigator determines that continuing treatment with CBD would not be in the best interest of the partient. 5. History of clinically significant gastrointestinal, renal, hepatic, neurologic, hematologic, endocrine, oncologic, pulmonary, immunologic, psychiatric, or cardiovascular disease, or other condition which would jeopardize safety or impact validity of results (per investigator). 6. Currently taking felbamate. 7. Compromised respiratory function or severe respiratory insufficiency. 8. Pregnant or lactating female. 9. In the opinion of the investigator, the participant is unsuitable in any other way to participate in this study.