- Positive screen for alcohol and/or drugs of abuse (including barbiturates, opiates, cocaine, cannabinoids, amphetamines and benzodiazepines). Note: Patients who currently take phenobarbital, mysoline or primidone as antiepileptic therapy and test positive for barbiturates are eligible for study participation. Patients who currently take vigabatrin or frisium as antiepileptic therapy and test positive for benzodiazepines are eligible for study participation.