This Phase 3 trial will enroll participants diagnosed with Lennox-Gastaut Syndrome (LGS) who are still experiencing at least 4 motor seizures involving the trunk or extremities per week, despite ongoing treatment with up to 3 antiepileptic drugs (AEDs) and who meet inclusion/exclusion criteria.

Following a 28-day baseline period, subjects will begin an 84-day treatment period. Participants will be assigned to receive twice daily doses of placebo or cannabidiol oral solution at the highest dose determined to be safe in a previous trial.

Following study completion, all subjects will be invited to receive Cannabidiol Oral Solution in an open label extension study (under a separate protocol).