This article is from the Epilepsy FAQ, by Andrew Patrick (email@example.com) with numerous contributions by others.
The drugs used to control seizures are called anticonvulsants. How they
stop the seizures, change the seizure threshold, or prevent electrical
discharges from occurring is not fully known. The neurochemical basis
for their action is also unknown. Research has shown that some of the
drugs can block the spread of abnormally fast nerve impulses in the
brain, while others can increase the flow of chloride ions, which
stabilize the nerve cells. Research is still being done in this area.