A Study of Possible Drug-drug Interactions Between Stiripentol or Valproate and Cannabidiol in Patients With Epilepsy

Note: Participants who enroll in Sweden must be aged 18-55 years. Key Inclusion Criteria: * Participant must be taking STP (for the STP arm) or VPA (for the VPA arm) and no more than 2 other antiepileptic drugs (AEDs) during the blinded period of the trial. * In the VPA arm only, the participant must not be receiving STP (VPA allowed in STP arm). * AED doses, including STP or VPA, must be stable for 4 weeks prior to screening and regimen must remain stable throughout the duration of the blinded period of the trial. * Participant must have a documented magnetic resonance imaging/computerized tomography of the brain that ruled out a progressive neurologic condition. * Participant must have experienced at least 1 countable uncontrolled seizure of any type (i.e., tonic-clonic, tonic, clonic, atonic, partial onset or focal: focal seizures with retained consciousness and a motor component, focal seizures with impaired consciousness, focal seizures evolving to bilateral secondary generalization) within 2 months prior to randomization. * Intervention with vagus nerve stimulation and/or ketogenic diet must be stable for 4 weeks prior to baseline and the participant must be willing to maintain a stable regimen during the blinded period of the trial. * Participant must abstain from alcohol during the blinded period of the trial. Key Exclusion Criteria: * Participant has clinically significant unstable medical conditions other than epilepsy. * Participant has a history of symptoms related to a drop in blood pressure due to postural changes (e.g., dizziness, light-headedness, blurred vision, palpitations, weakness, syncope). * Participant has a QT interval, corrected for heart rate with Bazett's formula (QTcB), greater than: * 450 msec for males. * 470 msec for females. * 480 msec if right bundle branch block is present. * Participant has any history of suicidal behavior or any suicidal ideation of type 4 or 5 on the C-SSRS in the last month or at screening. * Participant has had clinically relevant symptoms or a clinically significant illness in the 4 weeks prior to screening or enrollment, other than epilepsy. * Participant is currently using felbamate and has been taking it for less than 12 months prior to screening. * Participant has consumed alcohol during the 7 days prior to enrollment and is unwilling to abstain during the blinded phase of the trail. * Participant is currently using or has in the past used recreational or medicinal cannabis, or synthetic cannabinoid-based medications (including Sativex®) within the 3 months prior to trial entry. * Participant has any known or suspected history of any drug abuse or addiction. * Participant is unwilling to abstain from recreational or medicinal cannabis, or synthetic cannabinoid based medications (including Sativex) for the duration for the study. * Participant has consumed grapefruit or grapefruit juice 7 days prior to enrollment and is unwilling to abstain from drinking grapefruit juice within 7 days of pharmacokinetic visits. * Participant has any known or suspected hypersensitivity to cannabinoids or any of the excipients of the Investigational Medicinal Product (IMP), e.g., sesame oil. * Participant has received an IMP within the 12 weeks prior to the screening visit. * Participant has significantly impaired hepatic function at the screening or randomization visit, defined as any of the following: * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 5 × upper limit of normal (ULN). * ALT or AST \> 3 × ULN and total bilirubin (TBL) \> 2 × ULN or international normalized ratio (INR) \> 1.5. * ALT or AST \> 3 × ULN with the presence of fatigue, nausea, vomiting, right upper quadrant pain or tenderness, fever, rash, and/or eosinophilia (\> 5%).