Mysoline is effective against partial seizures, secondarily generalized seizures, and tonic-clonic seizures. It is not effective against other generalized seizure types, such as absence seizures or myoclonic seizures.

Effective serum concentrations generally range from 8-12 mg/L, though lower or higher concentrations may be necessary in some individual patients.

A VA Cooperative study in adults with partial and generalized tonic-clonic seizures (Mattson et al. 1985) showed that patients were more likely to stop taking Mysoline because of intolerable side effects than carbamazepine and phenytoin. However, CBZ was as effective as phenytoin and better tolerated than phenobarbital or primidone. The patients in this study who had tonic-clonic seizures achieved similar control from Mysoline as from the other medications used in the study (phenobarbital, carbamazepine and phenytoin). Of those in this group who took primidone for a year, 63% were seizure-free.

A similar study in children-which also included valproate-focused on the rate of side effects. Only 8% of the children who were given Mysoline had to stop taking it because of side effects.

Mysoline is most often used as adjunctive therapy in adults whose seizures are not well controlled by other medications.