The invention provides compositions and methods for treating seizure disorders such as epilepsy in humans and animals using, in a first embodiment, the combination of (i) an effective amount of a barbiturate drug, such as phenobarbital or primidone, which solely enhances GABAergic inhibition in a patient suffering a seizure disorder; and (ii) phytocannabinoid cannabidiol (CBD) in a dosage amount sufficient to overcome the hepatic metabolic effect stimulated by the barbiturate drug and provide bioavailable CBD to the patient in clinically efficacious amounts.