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

Pratama R, Muhaimin M, Khairinisa MA, Chaerunisaa AY · Ther Clin Risk Manag · 2026

can-nabis read · published 2026-08-19

The read

This is the update to the Devinsky Dravet trial covered above: instead of one syndrome and one trial, it pools seven randomized, placebo-controlled trials covering 1,154 patients with drug-resistant epilepsy across multiple syndromes, including Dravet, Lennox-Gastaut, and tuberous sclerosis complex.

The pooled result held up. Adjunctive CBD reduced seizure frequency significantly more than placebo, with a tight confidence interval that suggests the effect is real and reasonably consistent, not driven by one outlier trial. The benefit showed up across all three syndromes studied, which matters because drug-resistant epilepsies do not always respond the same way to the same intervention.

Dose and formulation mattered more than the headline number suggests. Oral, highly purified CBD at 20 mg per kilogram per day, the same dose used in the trials that led to Epidiolex's approval, produced the most consistent benefit. Liposomal CBD showed a modest effect. Transdermal CBD, the patch or cream format sold in a lot of consumer products, showed no measurable short-term benefit at all. If you are shopping for a CBD product hoping to reduce seizures, the delivery method is not a minor detail, it is the difference between a treatment with trial evidence behind it and one without any.

Safety tracked with what the original Dravet trial found: adverse events were mostly mild, but liver enzyme elevations and drowsiness showed up more often in patients also taking valproate or clobazam, two common anti-seizure medications. Anyone combining CBD with those drugs needs bloodwork monitoring, not just a start-and-forget approach.

What this paper found

Pooled 7 RCTs, 1,154 patients with drug-resistant epilepsy: adjunctive CBD significantly reduced seizure frequency vs. placebo (pooled RR 0.72, tight 95% CI, p < 0.0001).
Effect held consistently across Dravet syndrome, Lennox-Gastaut syndrome, and tuberous sclerosis complex.
20 mg/kg/day of oral, highly purified CBD (the Epidiolex dose) remains the efficacy benchmark; liposomal CBD showed modest benefit; transdermal CBD showed no short-term effect.
Adverse events were mostly mild, but liver enzyme elevation and somnolence were more common in patients also on valproate or clobazam.

Where it falls short

Pooling different syndromes and formulations into one effect size can hide meaningful differences between them.
Transdermal and liposomal CBD underperformed oral purified CBD, so 'CBD' is not one interchangeable product category.
Liver enzyme monitoring is necessary for patients combining CBD with valproate or clobazam, not optional.
Meta-analysis of existing trials, not a new trial. Long-term outcomes beyond the original studies' durations are still unaddressed.

Original abstract

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.

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Tagged conditions

Epilepsy →