Systematic Review Confirmed CBD Reduces Seizures in Treatment-Resistant Epilepsy | Research

The takeaway

CBD at 20 mg/kg/day was more effective than placebo for 50%+ seizure reduction (NNT=8) and complete seizure freedom in treatment-resistant epilepsy, though it also increased adverse and serious adverse events.

Epilepsy patients and families, neurologists, medical cannabis prescribers.

NNT of 8 for 50%+ seizure reduction means roughly 1 in 8 treatment-resistant epilepsy patients achieves meaningful benefit from CBD.

What the researchers found

CBD 20 mg/kg/day achieved 50%+ seizure reduction more than placebo (RR 1.74, NNT=8). CBD was more effective for complete seizure freedom (RR 6.17) and quality of life improvement (RR 1.73). However, it increased risk of adverse events (RR 1.24) and serious adverse events (RR 2.55). Observational studies showed 48.5% achieving 50%+ seizure reduction.

Why it matters

This systematic review provides the most comprehensive evidence base for CBD in epilepsy, quantifying both benefits and risks. The NNT of 8 for meaningful seizure reduction is clinically significant and compares favorably to many existing antiepileptic drugs.

The numbers in context

36 studies, mean age 16.1 years. NNT for 50%+ seizure reduction: 8 (CI 6-17). Complete seizure freedom RR: 6.17. QoL improvement RR: 1.73. AE RR: 1.24. SAE RR: 2.55. In observational studies: 48.5% achieved 50%+ reduction, 8.5% seizure-free.

How the study worked

Systematic review of 36 studies (6 RCTs, 30 observational) from Medline, Embase, and PsycINFO through October 2017. Mean participant age 16.1 years. Analyses in Stata 15.0.

What this study cannot tell us

Most RCT evidence was from pediatric populations with rare, severe epilepsy syndromes (Dravet, Lennox-Gastaut). Limited data on other epilepsy types and adult populations. Observational studies may overestimate effectiveness.

How to read the evidence

Strong - systematic review including 6 RCTs with quantitative synthesis, though most evidence comes from specific pediatric syndromes.

When this study was published

Published in 2018. CBD (Epidiolex) has since been FDA-approved for these indications.

The bigger picture

The evidence from RCTs and observational studies converges: CBD provides meaningful seizure reduction for a substantial proportion of patients with treatment-resistant epilepsy. The higher rate of serious adverse events warrants monitoring but does not outweigh benefits in this severe population.

Questions still open

Will CBD prove effective for common adult epilepsy syndromes? What is the optimal dosing for different seizure types? Can the adverse event profile be improved with different formulations or gradual dose titration?

Common questions

How effective is CBD for seizures?

This systematic review found that CBD at 20 mg/kg/day helped about 1 in 8 treatment-resistant epilepsy patients achieve 50% or greater seizure reduction. About 8.5% became completely seizure-free. These are meaningful results for a population where multiple other drugs have failed.

What are the risks of CBD for epilepsy?

CBD increased adverse events (mostly mild/moderate) and serious adverse events (RR 2.55) compared to placebo. However, the benefits for treatment-resistant patients generally outweigh these risks, especially when multiple other medications have failed.

Read the original research

Evidence for cannabis and cannabinoids for epilepsy: a systematic review of controlled and observational evidence.

Journal of neurology, neurosurgery, and psychiatry, 89(7), 741-753

View on PubMed ↗Publisher’s paper ↗

Citation

Stockings, Emily; Zagic, Dino; Campbell, Gabrielle; Weier, Megan; Hall, Wayne D; Nielsen, Suzanne; Herkes, Geoffrey K; Farrell, Michael; Degenhardt, Louisa. (2018). Evidence for cannabis and cannabinoids for epilepsy: a systematic review of controlled and observational evidence.. Journal of neurology, neurosurgery, and psychiatry, 89(7), 741-753. https://doi.org/10.1136/jnnp-2017-317168