Utility of Amantadine Hydrochloride in the Treatment of Post-traumatic Irritability

Inclusion Criteria: * Closed head injury (defined as brain injury or impaired brain function resulting from externally inflicted trauma without penetrating injury) at least 6 months prior to enrollment. * Age at time of enrollment: 16 - 65 inclusive (i.e., on or after 16th birthday, up to day before 66th birthday). * Voluntary informed consent of patient and informant. * Subject and informant willing to comply with the protocol, \& are available for all scheduled clinic visits. * Neuropsychiatric Inventory (NPI) Irritability Domain score \> 2. * Medically and neurologically stable during the month prior to enrollment. * If taking antidepressant, anxiolytic, hypnotic, or stimulant medications, no change anticipated in these medications during the month prior to enrollment. * No change in therapies or medications planned during the 28-day participation. * No surgeries planned during the 28-day participation. * Vision, hearing, speech, motor function, and comprehension must be sufficient for compliance with all testing procedures. Ability to interact and verbalize sufficient to participate in assessments. * Informant (family member or close friend) who lives with the participant with daily interaction in order to observe occurrences of irritability. Exclusion Criteria: * Patients without a reliable informant * Penetrating head injury * Injury \< 6 months prior to enrollment * Inability to interact sufficient for communication with caregiver * Acute and rehabilitation records unavailable or incomplete * DSM-IV diagnosis of schizophrenia or psychosis * Diagnosis of progressive or additional neurologic disease (such as, Alzheimer's disease, parkinson's disease, multi-infarct dementia, other cerebrovascular disorders with dementia, prior cerebrovascular accident, Huntington's disease, olivopontocerebellar atrophy, multisystem atrophy, multiple sclerosis, ALS, CNS tumor, progressive supranuclear palsy). * Diagnosis of seizure in the month prior to enrollment. * Previous allergy or adverse reaction to study drug * Ingestion of amantadine hydrochloride during the month prior to enrollment. * Concomitant use of neuroleptic agents or phenelzine * Creatinine clearance \<60 * Pregnancy (Beta-HCG performed on all females of child-bearing potential) and lactating females. * Clinical signs of active infection