While animal experimental data clearly suggest a potential benefit, supportive clinical data are quite sparse. In a case-control study of 308 cases of new onset seizures, Brust and colleagues found that marijuana use was significantly less prevalent among men who had unprovoked seizures compared to case controls. This difference was not significant in women. The authors suggest a potential protective effect against seizures with marijuana use; however, this should be considered speculative.
A survey of patients seen in a tertiary epilepsy center found that 21% of patients admitted to using marijuana in the last year, and 24% of patients believed marijuana to be effective for their seizures. While interesting, this anecdotal observation does not rise to the level of evidence needed to evaluate a potential new therapeutic modality.
Gloss and Vickrey conducted a Cochrane systematic review of the use of CBD in the treatment of epilepsy. Their methodology included only those trials that were randomized and controlled and excluded case series, case reports, and expert opinion. They were able to identify only 4 randomized controlled studies reported in the literature, and they included a letter to the editor and an abstract. The total number of subjects enrolled in these studies was 48. While only four studies and a letter to the editor were in the actual analysis, the authors included a complete reference listing of all articles reviewed for inclusion.
These reports suffered from a number of design flaws, including incomplete baseline quantification of baseline seizure frequency, indeterminate time periods for outcome determination and, in some cases, inadequate (or missing) statistical analysis—in general, a lack of sufficient detail to adequately evaluate and interpret the findings. Limitations aside, several studies did report that administration of adjunctive CBD did not result in meaningful changes in seizure frequency.
Cunha et al. reported a 2-phase pilot study of CBD versus placebo in normal volunteers and patients with refractory secondarily generalized epilepsy. In the first phase, 8 normal volunteers received CBD or placebo in a doubled-blind fashion, at a dose of 3 mg/kg for 30 days. The second phase was also double-blinded in 15 patients with epilepsy receiving 200 to 300 mg daily of CBD or placebo for 135 days. Patients continued baseline AED. All subjects tolerated CBD well, with no serious adverse events. Four of the epilepsy patients receiving CBD were “almost free of convulsive crisis” for the duration of the study. Three other patients receiving CBD had a partial reduction in seizures, and 1 subject had no response. Of the 7 patients receiving placebo, seizure frequency was unchanged in 6, and 1 had clear improvement in seizure control.
Using rigorous review methodology, Gloss and Vickery conclude that based on the low quality of the reports available, there is insufficient data available to draw any conclusions regarding the efficacy and or long-term safety of CBD in treating epilepsy. From the data available, it does appear that daily doses of 200 to 300 mg were safe in this small group of patients for a short period of time.
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