Government drug-buying agency Pharmac is to fund a new epilepsy treatment from Sunday.

Lacosamide will be fully funded for anyone whose epilepsy symptoms are not properly controlled by currently-funded medication as well as anyone who suffers adverse side-effects from those treatments.

"Epilepsy is a condition that can have a profound effect on people's lives, Pharmac medical director Peter Moodie said.

"Having a range of treatments to try is important, so it's pleasing to be able to widen the availability to include lacosamide."

Pharmac estimated 400 people would be prescribed lacosamide over the next three years.