An overview of the research evidence on cannabis and cannabinoids in the treatment of epilepsy
| 50% reduction in seizures n=19 studies (2 RCTs) | Complete seizure freedom n=17 studies (3 RCTs) | Quality of life n=14 studies (2 RCTs) | Withdrawals n=12 studies (4 RCTs) | Adverse events n=16 studies (4 RCTs) | |
| Cannabis sativa/extract | Two studies (no RCT) | No studies | Two studies (no RCT) | No studies | Two studies (no RCT) |
| Findings | Positive effect | Positive effect | AEs reported by 13% | ||
| Evidence GRADE | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ||
| Risk of bias | Serious to critical risk | Critical risk | Critical risk | ||
| Conclusion | Insufficient evidence | Insufficient evidence | Insufficient evidence | ||
| CBD | 11 studies (2 RCT) | 13 studies (3 RCT) | 9 studies (2 RCT) | 8 studies (3 RCT) | 11 studies (4 RCT) |
| Findings | Small effect | Positive effect | Positive effect | Patients more likely to withdraw from CBD | AEs reported by 11%–100% |
| Evidence GRADE | ⨁⨁◯◯ LOW | ⨁⨁◯◯ LOW | ⨁⨁◯◯ LOW | ⨁⨁◯◯ LOW | ⨁⨁◯◯ LOW |
| Risk of bias | Low to serious risk | Low to critical risk | Low to critical risk | Low to critical risk | Low to critical risk |
| Conclusion | Some evidence of effect | Some evidence of effect | Some evidence of effect | Greater likelihood of withdrawal | Mild-to-moderate AEs likely |
| Oral THC | No studies | No studies | No studies | No studies | One study (no RCT) |
| Findings | AEs reported by 12.5% | ||||
| Evidence GRADE | ⨁◯◯◯ VERY LOW | ||||
| Risk of bias | No information | ||||
| Conclusion | Insufficient evidence | ||||
| CBD:THC | Five studies (no RCTs) | Three studies (no RCTs) | Two studies (no RCT) | Two studies (no RCT) | Two studies (no RCT) |
| Findings | Positive effect | Small effect | Positive effect | Withdrawal rate 14% | AEs reported by 42% |
| Evidence GRADE | ⨁⨁◯◯ LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW |
| Risk of bias | Serious to critical risk | Serious to critical risk | Serious risk | Serious risk | Serious to critical risk |
| Conclusion | Insufficient evidence | Insufficient evidence | Insufficient evidence | Insufficient evidence | Insufficient evidence |
| Oral cannabis extracts | One study (no RCT) | One study (no RCT) | One study (no RCT) | One study (no RCT) | No studies |
| Findings | Positive effect | Small effect | Positive effect | Withdrawal rate 15% | |
| Evidence GRADE | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | ⨁◯◯◯ VERY LOW | |
| Risk of bias | Critical risk | Serious risk | Serious risk | Serious risk | |
| Conclusion | Insufficient evidence | Insufficient evidence | Insufficient evidence | Insufficient evidence |
Risk of bias=low to high in randomised trials; low to critical risk in non-randomised studies, no information where information not available.
GRADE ratings: high: we are very confident that the true effect lies close to that of the estimate of the effect; moderate: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different; low quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect; very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
CBD, cannabidiol; GRADE, Grades of Recommendation, Assessment, Development and Evaluation; RCT, randomised controlled trial; THC, tetrahydrocannabinol,.