Abstract 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...