Adjunctive Cannabidiol for Drug-Resistant Epilepsy: A Systematic Review and Meta-Analysis of Randomized Trials Across Syndromes, Formulations, and Dose Ranges.

BACKGROUND

Cannabidiol (CBD) has emerged as a promising adjunctive therapy for drug-resistant epilepsy, yet clinical findings remain heterogeneous across trials. This meta-analysis aimed to evaluate the efficacy, safety, and formulation-dependent performance of CBD in patients with treatment-resistant epilepsies.

METHODS

A systematic review and meta-analysis were conducted in accordance with PRISMA 2020 guidelines, including randomized, double-blind, placebo-controlled trials of adjunctive CBD in drug-resistant epilepsy. Literature was sourced from PubMed/MEDLINE, Scopus, and the Cochrane Central Register of Controlled Trials (CENTRAL). Data were synthesized using random-effects models to estimate pooled risk ratios (RRs) with 95% confidence intervals (CIs) for seizure reduction and adverse events. Subgroup analyses explored the influence of epilepsy syndrome, CBD dose, and formulation type.

RESULTS

Seven randomized controlled trials involving 1154 participants met inclusion criteria. Adjunctive CBD significantly reduced seizure frequency compared with placebo (pooled RR = 0.72, 95% CI 0.71-0.73; p < 0.0001). The effect was consistent across Dravet syndrome, Lennox-Gastaut syndrome, and tuberous sclerosis complex, with optimal efficacy observed at 20 mg/kg per day of highly purified oral CBD. Liposomal CBD produced modest benefit, whereas transdermal formulations showed no short-term efficacy. Adverse events were predominantly mild and comparable to placebo, although elevations in hepatic enzymes and somnolence occurred more frequently in patients receiving concomitant valproate or clobazam.

CONCLUSION

Adjunctive oral CBD provides a reproducible and clinically meaningful reduction in seizures in drug-resistant epilepsy, with an acceptable safety profile. Oral CBD at 20 mg/kg per day represents the current benchmark for efficacy, while alternative formulations require further evaluation. Future research should address long-term outcomes, optimal dosing strategies, and formulation refinement to improve tolerability and accessibility in diverse epileptic populations.