My Father In Law Has Been Drinking Sassafrass Tea, Made

My father in law has been drinking sassafrass tea, made from the root and purchased at a heath food store.
He says it has stopped him from having almost daily bouts of diarrhea. Diarrhea is very seldom now. My sister brought it to my attention that safrole is very dangerous. He drinks this tea almost daily, if not every day. I'm concerned that he may be doing damage to his body. What do you think? He hasn't discussed it with his dr. either, and he is on quite a few prescriptions for health issues.