Seizures are a relatively nonspecific response of the cerebral cortex to insult and can be caused by a variety of toxic or metabolic diseases. Seizure in response to extracranial disease are called reactive seizures. Toxins cause seizures by altering the balance of excitation and inhibition in the nervous system or interfering with energy metabolism. Many therapeutic or illicit drugs will cause seizures through similar mechanisms. Metabolic diseases can cause seizures by interfering with energy metabolism, changing osmolality, or producing endogenous toxins. In addition, metabolic disease may alter the pharmacokinetics of antiepileptic drugs or drugs that have the potential to cause seizures. While seizures represent a serious sign for many of these conditions, reactive epilepsy always carries the possibility that the seizures may be eliminated if the underlying cause is detected and corrected.