When Neurontin (the brand name form of gabapentin) and an inactive placebo were both used as add-on therapy in careful studies Neurontin reduced seizure frequency by at least half in about 12% more people. Side effects were only a little more troublesome than with the placebo and often went away without stopping the Neurontin.

A study of add-on therapy in children aged 3 to 12 years had similar results. Children with complex partial seizures and secondarily generalized seizures showed the greatest improvement.

No single combination of seizure medicines is perfect for everyone. Sometimes, a series of combinations must be tried before finding what is best for the individual. Because gabapentin generally does not interact with other medications, no adjustments are needed when it is used in combination with other seizure medicines. This feature also makes it a good choice for people (such as many elderly people with epilepsy) who need to take medicine for other disorders.

Studies have also looked at the effectiveness of Neurontin (brand name form of gabapentin) used alone. In one study, people with newly diagnosed partial seizures were treated with either Neurontin or carbamazepine (Tegretol, Carbatrol). In this study, Neurontin and Tegretol had a similar effect on the occurrence of seizures, but fewer people taking Neurontin had to withdraw because of side effects.

Another study looked at people who had been taking one or two other seizure medicines but continued to experience complex partial seizures or secondarily generalized seizures. These people were gradually switched to Neurontin used alone at various doses. Each person had to withdraw from the study if he or she started to have more frequent seizures. Overall, 20% completed 16 weeks of treatment with Neurontin alone. This percentage was higher for those who had previously been taking only one seizure medicine, but it was lower for those who had been taking carbamazepine (Tegretol, Carbatrol).