Table 4

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/extractTwo studies (no RCT)No studiesTwo studies (no RCT)No studiesTwo studies (no RCT)
  FindingsPositive effectPositive effectAEs reported by 13%
  Evidence GRADE⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW
  Risk of biasSerious to critical riskCritical riskCritical risk
  ConclusionInsufficient evidenceInsufficient evidenceInsufficient evidence
CBD11 studies (2 RCT)13 studies (3 RCT)9 studies (2 RCT)8 studies (3 RCT)11 studies (4 RCT)
  FindingsSmall effectPositive effectPositive effectPatients more likely to withdraw from CBDAEs reported by 11%–100%
  Evidence GRADE⨁⨁◯◯ LOW⨁⨁◯◯ LOW⨁⨁◯◯ LOW⨁⨁◯◯ LOW⨁⨁◯◯ LOW
  Risk of biasLow to serious riskLow to critical riskLow to critical riskLow to critical riskLow to critical risk
  ConclusionSome evidence of effectSome evidence of effectSome evidence of effectGreater likelihood of withdrawalMild-to-moderate AEs likely
Oral THCNo studiesNo studiesNo studiesNo studiesOne study (no RCT)
  FindingsAEs reported by 12.5%
 Evidence GRADE⨁◯◯◯ VERY LOW
  Risk of biasNo information
  ConclusionInsufficient evidence
CBD:THCFive studies (no RCTs)Three studies (no RCTs)Two studies (no RCT)Two studies (no RCT)Two studies (no RCT)
  FindingsPositive effectSmall effectPositive effectWithdrawal rate 14%AEs reported by 42%
  Evidence GRADE⨁⨁◯◯ LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW
  Risk of biasSerious to critical riskSerious to critical riskSerious riskSerious riskSerious to critical risk
  ConclusionInsufficient evidenceInsufficient evidenceInsufficient evidenceInsufficient evidenceInsufficient evidence
Oral cannabis extractsOne study (no RCT)One study (no RCT)One study (no RCT)One study (no RCT)No studies
  FindingsPositive effectSmall effectPositive effectWithdrawal rate 15%
 Evidence GRADE⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW⨁◯◯◯ VERY LOW
  Risk of biasCritical riskSerious riskSerious riskSerious risk
  ConclusionInsufficient evidenceInsufficient evidenceInsufficient evidenceInsufficient 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,.