Brain cells need to work (fire) at a certain rate to function normally. During a seizure, brain cells are forced to work much more rapidly than normal. Valproic acid helps prevent brain cells from working as fast as a seizure requires them to. In this way, seizures can be stopped when they are just beginning. We don't fully understand exactly how valproic acid works. Like other forms of valproate, it appears to work in several ways at once. This may explain why it's effective against so many types of seizures.

When usual amounts are taken, there is little or no change in normal patterns. If the amount of medicine in the blood gets very high, however, valproic acid can impair the function of healthy brain cells.