I have used Trileptal during my TN journey. It stops the pain completely for me.
However, tell your friend that his/her doctor should be performing blood tests every three months. Trileptal can cause low blood sodium levels that can adversely affect the kidneys and the blood tests will monitor that.
It can cause drowsiness, but my doctor had me take a NoDoz with the daytime doses to counteract that. One caution with that is, some people have a pain trigger with caffeine. The doctor should be asked if this suggestion is ok.