Most authors report that antiepileptic drugs provide complete control for more than half of all patients with epilepsy, and reduce the number of seizures in another 20–30 percent. The remaining 20 percent do not respond to current medications and their condition is termed “intractable” or “refractory to treatment.” Some of these people may have other treatment options, such as surgery, or (in children) the ketogenic diet.

Reports in the medical literature suggest between 75 and 80 percent of patients with idiopathic, generalized epilepsy have reliable, long term control of seizures on currently available drugs. Some patient surveys, however, show larger percentages of people continuing to have seizures, although they may describe their condition as being under control.

Selection bias (clinic-based survey respondents may be more severely affected) may have some bearing on these different results; also, physicians and patients may have different interpretations of control.