Inclusion Criteria:

1. Male or non-pregnant, non-lactating female, age 12 to 65 years who have satisfactorily completed study LP352-201
2. Diagnosis of Dravet syndrome, Lennox-Gastaut syndrome, or other developmental and epileptic encephalopathy
3. The patient/parent/caregiver is able and willing to attend study visits, complete the diary and take study drug as instructed

Exclusion Criteria:

1. Had an SAE in Study LP352-201 that was definitely, probably, or possibly related to exposure to study drug
2. Current or past history of cardiovascular or cerebrovascular disease, such as cardiac valvulopathy, myocardial infarction, stroke, pulmonary arterial hypertension or abnormal blood pressure
3. Has glaucoma, renal impairment, liver disease or any other medical condition that would affect study participation or pose a risk to the subject
4. Current or recent history of moderate or severe depression, anorexia nervosa, bulimia or at risk of suicidal behavior
5. Currently taking anorectic agents, monoamine oxidase inhibitors; serotonin agonists or antagonists including fenfluramine, atomoxetine, vortioxetine, or other medications for weight loss
6. Positive test result on the drug screen, except tetrahydrocannabinol (THC) for patients taking prescribed cannabidiol