A total of 27 patients with medically intractable complex partial seizures has been investigated for effects of anticonvulsant drugs on mental abilities, particularly on verbal memory performance. Fourteen patients with right (RTLE) and 13 with left (LTLE) temporal lobe epilepsy have been tested with a word list learning paradigm under the conditions of full and reduced anticonvulsant medication. Memory performance has significantly improved with drug reduction, however only for the LTLE group. In addition, significant group differences for verbal memory between LTLE and RTLE subjects under full medication have completely disappeared with drug reduction. Finally this investigation demonstrates, that very specific and circumscribed steps of verbal memory processing, particularly retrieval abilities after interference, are affected by anticonvulsants. These findings underline the importance of pharmacological effects on cognition and suggest to reevaluate their relevance compared to other contributing factors.