Anything methylated is going to be hard on the liver.
To answer your question as to how hard, I don't know.
Put it this way, I know people who have abused pro-hormones or even taken insane amounts of dbol, winnie, and other orals for long periods of time. They turned out fine and their docs tell them that their liver turned out fine.
Some people may do one cycle of prohormones properly and their liver goes to shit.
I don't know exaclty how to convey my point except to just say --use at your own risk.
I must say I have NO experience, just research.
I feel that if somebody where to go in for bloodwork, checkups, etc and treat a prohormone as they would an oral steroid then they CAN be fine. *emphasis on CAN because you never know with messing with your body's endocrine system, especially with drugs that have little research on them.
Hope that helped.