Zonisamide is proven effective for partial epilepsy in adults.

The FDA-approved information on zonisamide focuses on three studies involving a total of 499 patients who had frequent partial-onset seizures (with or without secondary generalization) uncontrolled by multiple drugs. During the 3 months that each study lasted, the patients were given increasing doses of either zonisamide or a placebo (an inactive substance), in addition to the medication they were previously taking. The researchers measured the average (median) percent reduction in the frequency of partial seizures. They also looked at the percentage of patients whose seizures were reduced more than 50% ("responders"). Here are the results:

Study	Median % Reduction in partial seizures		% Responders(at least 50% fewer seizures)
	Zonegran	Placebo	Zonegran	Placebo
Study1	40.5%	9.0%	41.8%	22.2%
Study2	29.6%	-3.2%	29.0%	15.0%
Study3	27.2%	-1.1%	28.0%	12.0%

The patients taking zonisamide had a significant reduction in the number of seizures, and more of them had at least 50% fewer seizures, compared to the patients who received the placebo.

Recent small studies have shown that zonisamide has potential benefits for a broad spectrum of other types of epilepsy, such as Lennox-Gastaut syndrome, infantile spasms, and progressive myoclonus epilepsy (PME), though further research is needed.