Research on Cognitive Effect of Cannabidiol on Dravet Syndrome and Lennox-Gastaut SyndromeGastaut Syndrome

Selection criteria of the patients are as below: 1. Age: 2 years old to 18 years old 2. Investigation center: Severance hospital, Yonsei University College of Medicine, Seoul, Korea 3. A) Diagnosed as Dravet syndrome by clinical manifestations and/or genetic test B) Diagnosed as Lennox-Gastaut syndrome by clinical manifestations and electroencephalography 4. The diagnosed patients by criteria 3-(1) or 3-(2) with intractable seizures after using over two antiepileptic medications 5. Patients and caregivers who agreed to participation in this trial Exclusion criteria of the patients are as below: 1. Patients with possibility of progressive central nervous system disease other systemic disease 2. The patients who started additional antiepileptic medication during the investigation period, with exception of short-term acute treatment of seizures (e.g. benzodiazepine for rescue therapy) 3. Patients with alanine and aspartate aminotransferase and/or total bilirubin levels over 2 times of the normal range, or blood urea nitrogen and creatinine ratio over 3 times of the normal range 4. Patient with hypersensitivity or allergic reactions to cannabidiol 5. patients who are incapable of executing cognitive tests, or cases whom the investigators consider inappropriate to be enrolled in the trial Overall trial schedule for each patient is as follows: A) Baseline Phase (2 weeks) * Baseline Phase starts from the screening visit, where the patient and caregiver write permission to the trial and goes through laboratory, electroencephalography, and neuropsychological tests. B) Treatment Period : Titration(2 weeks) + stabilization period (10 weeks) + maintenance period (12 weeks) * Titration: cannabidiol titration up to 10mg/kg/day with the caregiver monitoring the patient's tolerability * Stabilization: caregiver monitoring the patient's tolerability, with no change in medication dosage * Maintenance: no change in medication dosage * Statistical analysis of outcomes would be done as follows: T-test would be done to compare each test before and after cannabidiol treatment. For multiple results along the intervention time period, repeated data analyses would be done. Continuous variables would be evaluated by repeated measures analysis of variance or generalized estimating equations. Nominal variables would be evaluation by chi-squared test or trend test. Evaluation of seizure outcomes would include all patients who completed the 24-week medication and those who dropped out of the study, either by follow-up loss or discontinuation of medication due to incomplete seizure control or adverse effect of the medication.