Valproic acid and the other forms of valproate are highly effective seizure medicines. Their effectiveness in controlling seizures has been extensively studied in careful scientific studies involving thousands of people. (There is little difference in effectiveness between valproic acid and the other types, like Depakote, so we will use the general term "valproate.")

Valproate works against almost every type of epilepsy. It was first approved to treat absence seizures. In a number of studies, valproate has completely controlled absence seizures in a high proportion of people, and it is widely regarded as the first-choice medication for most people with absence seizures. Complete control seems more likely when the absence seizures appear alone than when they are combined with another seizure type (Sato et al., 1982).

Most experts also regard valproate as the first choice for treating generalized tonic-clonic seizures. One study (Wilder et al., 1983) compared it with Dilantin (phenytoin) in treating a group of people with newly diagnosed generalized tonic-clonic, clonic, or tonic seizures. Of the people treated with valproate, 82% had no seizures during the study period after the level of valproate in the blood reached a high enough level. The comparable figure for those who took phenytoin was 76%.

Valproate also works to control seizures triggered by flashing lights (photosensitivity) and it seems to be effective for myoclonic seizures in many situations.

Epilepsy syndromes that involve symptomatic generalized seizures, such as infantile spasms and Lennox-Gastaut syndrome, are less well controlled by valproate (or any other medication). Nevertheless, valproate is usually regarded as the first choice for treating these conditions. Some people improve enough that they can reduce their use of other seizure medicines that have more troubling side effects.

Researchers looked at whether valproate alone can be used effectively to treat partial seizures. One large study (Mattson et al., 1992) found Tegretol (carbamazepine) to be more effective than valproate in controlling complex partial seizures, but valproate was shown to be a valuable alternative. Differences in the side effects may make it a better choice for some people.

If valproic acid (valproate) alone does not fully control a person's seizures, a combination of valproic acid and another seizure medicine may be more effective. No single combination is perfect for everyone. Sometimes a series of combinations must be tried before finding what is best for that individual.

Valproic acid or other forms of valproate are often used as "add-on" medications for people who continue to have complex partial seizures while taking other seizure medicines. In one study, 144 such people were given either valproic acid or a placebo (sugar pill) in addition to the Dilantin or Tegretol that they were already taking. The patients who took valproic acid had just over half as many seizures as before, while the people who took the placebo had a significantly smaller decrease.