The efficacy and safety of cannabidiol as adjunct treatment for drug‐resistant idiopathic epilepsy in 51 dogs: A double‐blinded crossover study

BACKGROUND: Approximately 30% of dogs with idiopathic epilepsy (IE) are drug‐resistant. Recent studies have suggested cannabidiol (CBD) may be an effective anticonvulsant in dogs with IE. OBJECTIVE: To evaluate the addition of CBD to antiseizure drugs (ASDs) on seizure frequency and to report adverse events in dogs with drug‐resistant IE. ANIMALS: Fifty‐one dogs. Dogs having at least 2 seizures per month while receiving at least 1 ASD were included in the trial. METHODS: Double‐blinded placebo‐controlled crossover study. The 5 mg/kg/day dosage met futility requirements after 12 dogs, and a dosage of 9 mg/kg/day was used in the next 39 dogs. Dogs were randomly assigned to receive CBD or placebo for 3 months, with a 1‐month washout period between oils. Total numbers of seizures and seizure days were recorded. Diagnostic testing was performed periodically throughout the trial. RESULTS: At the 9 mg/kg/day dose, the decrease in total seizure frequency was significant compared with placebo. A 24.1% decrease in seizure days occurred in dogs receiving CBD and a 5.8% increase occurred in dogs receiving placebo (P ≤ .05). No significant difference was found in the number of responders (≥50% decrease in total seizures or seizure days). Liver enzyme activities increased at both dosages. Decreased appetite and vomiting were more common in the CBD phase (P ≤ .05). CONCLUSIONS AND CLINICAL IMPORTANCE: Cannabidiol decreased total seizures and seizure days compared to placebo when administered to dogs PO at 9 mg/kg/day. Liver enzymes should be monitored with administration of CBD in dogs.