Although M4OHN has fewer adverse side effects than some of the nastier methyls like M 1-T, I would not call it liver friendly. Do we really have any data supporting a low or non-hepatotoxic effect of M4OHN on the liver?
Regarding Milk Thistle reducing the effectiveness of prohormones, the idea was based on an article written by Big Cat over at BB.com where he hypothesized that improving the liver's function by using milk thistle would therefore help the liver remove prohormones from the body. He just stated it without proof. From there, it has gone on to be an "urban legend" in the bodybuilding community. Note: I am not saying that it is not true, merely that there is no evidence supporting that claim. (If anyone has scientific information to the contrary, I would appreciate it if they posted it.) Let me add that NAC and Milk Thistle help the liver recover from damage, they do not necessarily protect it from damage.