CBD for Epilepsy Finally Has Hard Evidence, but a Drug Interaction Complicates the Picture | Research

The takeaway

Three placebo-controlled trials confirmed that pharmaceutical CBD reduces seizures in Dravet syndrome and Lennox-Gastaut syndrome, but a significant drug interaction with clobazam makes it unclear whether the benefits come from CBD itself or from elevated levels of the co-medication.

Readers following the CBD-for-epilepsy evidence, including patients and caregivers.

First class 1 evidence that CBD reduces seizures in Dravet syndrome and Lennox-Gastaut syndrome

What the researchers found

After years of uncontrolled observations and anecdotal reports, three rigorous placebo-controlled trials of purified CBD (Epidiolex) provided the first class 1 evidence that CBD improves seizure control in specific epilepsy syndromes.

In Dravet syndrome, CBD reduced the frequency of convulsive seizures (tonic-clonic, tonic, clonic, and atonic) compared to placebo. In Lennox-Gastaut syndrome, CBD reduced the frequency of drop seizures.

However, the review raises a critical complication: CBD markedly increases plasma levels of N-desmethylclobazam, the active metabolite of clobazam, a commonly co-prescribed anti-seizure medication. Many trial participants were taking clobazam, meaning some of the observed seizure reduction could be due to this drug interaction rather than a direct anti-seizure effect of CBD. The author argues that subgroup analyses of patients not taking clobazam are needed to resolve this question.

Why it matters

This review marks a turning point in the evidence base for CBD in epilepsy. For the first time, controlled trial evidence confirmed what families and clinicians had reported anecdotally for years. But the author's identification of the clobazam interaction as a potential confound is important: if a significant portion of the benefit comes from boosted clobazam levels, then CBD's direct anti-seizure effect may be smaller than the headline results suggest.

The numbers in context

Three placebo-controlled trials completed. CBD reduced convulsive seizures in Dravet syndrome and drop seizures in Lennox-Gastaut syndrome vs. placebo. CBD significantly increased N-desmethylclobazam plasma levels in patients co-medicated with clobazam.

How the study worked

Comprehensive narrative review covering the preclinical anticonvulsant profile of CBD, uncontrolled clinical observations with CBD-enriched extracts, and the three pivotal placebo-controlled adjunctive-therapy trials in Dravet syndrome and Lennox-Gastaut syndrome.

What this study cannot tell us

The review is authored by a single expert and is not a formal systematic review. The clobazam interaction concern, while scientifically valid, has not been definitively resolved by the time of this review. The trials studied pharmaceutical-grade CBD, not over-the-counter CBD products, which vary widely in quality and composition.

How to read the evidence

Strong evidence: the review covers three placebo-controlled randomized trials providing class 1 evidence, though with the clobazam interaction caveat.

When this study was published

Published in 2017, shortly after the pivotal trials that led to Epidiolex FDA approval in 2018.

The bigger picture

The CBD-epilepsy story illustrates both the promise and complexity of cannabinoid medicine. Hard evidence arrived, confirming real clinical benefit, but also revealed pharmacological nuances (drug interactions) that complicate interpretation. This pattern of "it works, but the mechanism may not be what we assumed" is a recurring theme in cannabinoid research.

Questions still open

How much of CBD's anti-seizure effect is direct versus mediated through boosted clobazam levels? Does CBD reduce seizures in patients not taking clobazam? Are CBD-enriched extracts (containing trace amounts of other cannabinoids) more effective than purified CBD alone?

Common questions

Does CBD work for all types of epilepsy?

The controlled trial evidence at the time of this review was specific to Dravet syndrome and Lennox-Gastaut syndrome, both severe childhood epilepsy syndromes. Whether CBD helps other epilepsy types was not established by these trials.

What is the clobazam interaction and why does it matter?

CBD significantly increases blood levels of N-desmethylclobazam, the active breakdown product of the anti-seizure drug clobazam. Since many trial participants were taking clobazam, some of the seizure reduction attributed to CBD may actually have resulted from having more clobazam metabolite in their system. This makes it harder to know how much benefit comes from CBD directly.

Read the original research

Cannabinoids in the Treatment of Epilepsy: Hard Evidence at Last?

Journal of epilepsy research, 7(2), 61-76

View on PubMed ↗Publisher’s paper ↗

Citation

Perucca, Emilio. (2017). Cannabinoids in the Treatment of Epilepsy: Hard Evidence at Last?. Journal of epilepsy research, 7(2), 61-76. https://doi.org/10.14581/jer.17012