Gabapentin is used to treat seizures that begin in a limited area of the brain. These are called partial seizures. Some of them spread throughout the rest of the brain. They are called secondarily generalized seizures. Gabapentin does not prevent seizures that begin on both sides of the brain at the same time, called primary generalized seizures.

Gabapentin is usually used as an additional seizure medicine when another medicine has not been able to control all of a person's partial seizures. This kind of use is called add-on or adjunctive therapy. Gabapentin was usually used in this way when it was being tested, so the U.S. Food and Drug Administration (FDA) has only approved it as add-on therapy. Gabapentin is easy to use as an add-on because it does not interact with other seizure medicines.

Sometimes gabapentin is also used alone to treat partial seizures, although the FDA has not approved it to be used in this way.