This chapter emphasizes the spectrum and scale of antiepileptic drugs (AED) usage in medical disciplines other than epilepsy, and to increase awareness of unpredicted drug interactions when combination therapy with two/three drugs is used. There are many pharmacological reasons why AEDs have therapeutic effects in non-epileptic neurological and psychiatric conditions. The fact that over-the-counter drugs and nutritional supplements are increasingly being self-administered by patients creates the risk of drug interactions. In many countries folk medicine is frequently used for various reasons. Carbamazepine (CBZ) is one of the most commonly used AEDs in epilepsy and other neurological and psychiatric disorders. Many drug interactions can be demonstrated but only a few of them are so clinically significant that they require adjustment of drug dosages. Case reports of toxic effects due to drug interactions are presented in the chapter as a warning signal calling for attention when polytherapy has to be used.