Transdermal CBD’s Open-Label Seizure Improvement Did Not Reverse Its Blinded Null Result
Transdermal CBD did not significantly reduce seizure frequency compared with placebo during a blinded adult focal-epilepsy trial. Improvement during the later open-label extension answered a different question and did not overturn that randomized comparison.
A daily-dose distinction clarified by correction
The trial randomized 188 adults to transdermal CBD or placebo. The corrected dose description specifies 195 mg or 390 mg daily. Published corrections addressed dosing wording in the abstract and visual abstract, and a separate collaborator-list omission.
At 12 weeks, neither CBD group significantly separated from placebo on seizure frequency. The reported comparisons had p values of 0.89 and 0.32. Those are efficacy findings for this population, formulation and treatment period.
The extension lacked a placebo comparison
Many participants entered an open-label extension, and substantial seizure reductions were reported over continued treatment. However, participants and investigators then knew active treatment was being given.
Without a concurrent blinded placebo group, the extension cannot separate medication effects from persistent placebo response, time, selection of continuing participants or other changes. The original authors explicitly discussed that limitation.
What the results leave open
The trial excluded clobazam, a medication with a known CBD interaction, and focal epilepsy is heterogeneous. Dose, formulation and duration could matter. These explanations are reasons for further research rather than proof that an unobserved blinded benefit existed.
The findings should not be generalized to every seizure syndrome or compared directly with oral-CBD trials without considering those differences. The defensible account preserves the null randomized endpoint, the separate extension observations and the corrected daily doses.
The dose correction is available at DOI 10.1001/jamanetworkopen.2022.28862. It concerns accurate reporting of administration, not a new positive efficacy result.
Related: How study design affects interpretation of CBD outcomes.
Primary research
Adjunctive Transdermal Cannabidiol for Adults With Focal Epilepsy: A Randomized Clinical Trial. JAMA Network Open (2022).
