A pharmaceutical composition comprises an anti-epileptic drug that does not inhibit, enhance or otherwise modify dextromethorphan binding to the central nervous system dextromethorphan receptor and an effective amount of dextromethorphan to potentiate the anticonvulsant activity of the drug. Other related compounds similar to dextromethorphan which inhibit or enhance dextromethorphan binding to the dextromethorphan site in the brain are also suitable as potentiating agents for the anticonvulsants. A method of treating epilepsy and other convulsions include the steps of introducing to the patient an effective amount of the compound comprising an anti-epileptic drug and potentiating amount of dextromethorphan or one of the related compounds.