Trimethadione is primarily used in the treatment of epilepsy, specifically for controlling petit mal seizures, also known as absence seizures. It helps stabilize electrical activity in the brain, reducing the occurrence of these seizures. However, its use has declined over time due to the development of newer antiepileptic drugs with fewer side effects. It is typically prescribed when other treatments are ineffective or unsuitable. Due to potential risks, such as teratogenic effects, it is avoided in pregnant women. Regular monitoring of blood levels and liver function is often required during treatment to ensure safety and efficacy.