Highly Purified Cannabidiol for Epilepsy Treatment: A Systematic Review of Epileptic Conditions Beyond Dravet Syndrome and Lennox–Gastaut Syndrome

Abstract
Background
Cannabidiol (CBD), which is one major constituent of the Cannabis sativa plant, has anti-seizure properties and does not produce euphoric or intrusive side effects. A plant-derived, highly purified CBD formulation with a known and constant composition has been approved by the US Food and Drug Administration for the treatment of seizures associated with Dravet syndrome, Lennox–Gastaut syndrome, and tuberous sclerosis complex. In the European Union, the drug has been authorized by the European Medicines Agency for the treatment of seizures associated with Dravet syndrome and Lennox–Gastaut syndrome, in conjunction with clobazam, and is under regulatory review for the treatment of seizures in patients with tuberous sclerosis complex.

Objectives
This systematic review aimed to summarize the currently available body of knowledge about the use of this US Food and Drug Administration/European Medicines Agency-approved oral formulation of pharmaceutical-grade CBD in patients with epileptic conditions, especially developmental and epileptic encephalopathies other than Dravet syndrome and Lennox–Gastaut syndrome.

Methods
The relevant studies were identified through MEDLINE and the US National Institutes of Health Clinical Trials Registry in October 2020. There were no date limitations or language restrictions. The following types of studies were included: clinical trials, cohorts, case-control, cross-sectional, clinical series, and case reports. Participants had to meet the following criteria: any sex, any ethnicity, any age, diagnosis of epilepsy, receiving plant-derived, highly purified (> 98% w/w) CBD in a sesame oil-based oral solution for the treatment of seizures. Data extracted from selected records included efficacy, tolerability, and safety outcomes.

Results
Five hundred and seventy records were identified by database and trial register searching. Fifty-seven studies were retrieved for detailed assessment, of which 42 were eventually included for the review. The participants of the studies included patients of both pediatric and adult age. Across the trials, purified CBD was administered at dosages up to 50 mg/kg/day. In a randomized double-blind controlled trial in patients with tuberous sclerosis complex, CBD was associated with a significantly greater percent reduction in seizure frequency than placebo over the treatment period. Open-label studies suggested the effectiveness of CBD in the treatment of children and adults presenting with other epilepsy syndromes than those addressed by regulatory trials, including CDKL5 deficiency disorder and Aicardi, Dup15q, and Doose syndromes, SYNGAP1 encephalopathy, and epilepsy with myoclonic absences. The most common adverse events observed during treatment with CBD included somnolence, decreased appetite, diarrhea, and increased serum aminotransferases.

Conclusions
The currently available data suggest that response to treatment with a highly purified, plant-derived CBD oil-based solution can be seen in patients across a broad range of epilepsy disorders and etiologies. The existing evidence can provide preliminary support for additional research.