It is primarily effective in treating absence seizures, but can also be used in refractory temporal lobe epilepsy.

Severe adverse reactions are possible, including Steven Johnson syndrome, nephrotoxicity, hepatitis, aplastic anemia, neutropenia, or agranulocytosis.

More common adverse effects include drowsiness, hemeralopia, and hiccups.

[1][2] If administered during pregnancy, fetal trimethadione syndrome may result causing facial dysmorphism (short upturned nose, slanted eyebrows), cardiac defects, intrauterine growth restriction (IUGR), and mental retardation.

The fetal loss rate while using trimethadione has been reported to be as high as 87%.