Neurobehavioral effects of phenytoin, carbamazepine, and valproic acid: implications for use in traumatic brain injury. Due to the risk of posttraumatic epilepsy, phenytoin, carbamazepine, and valproic acid are often prescribed for patients with traumatic brain injury (TBI). In this review the literature is examined for evidence of neurobehavioral impairment due to carbamazepine, phenytoin, and valproic acid. No comparative studies have been performed in the TBI population, making if difficult to determine if one of these medications is preferable. Direct inference from studies on epilepsy patients to TBI patients is hazardous due to underlying differences in the two populations. Reported findings for epilepsy patients are subtle and not consistent across studies. All three drugs appear to exert some effect on cognitive and motor functions in epileptic patients, and these impairments worsen at increasing serum levels. The varied length of experience with each drug makes it difficult to assign relative weight to the evidence for or against each. A comparative assessment of cognitive and behavioral effects of anticonvulsants should be done in the TBI population. 