The pbi article above seems to be entirely based on personal opinion motivated by a pure living agenda... it cites no studies in support. In comparison, here's a pretty comprehensive article that tries to make reference to most of the published studies on Silymarin, the main component of Milk Thistle:
I note that none of the concerns expressed in the pbi article seem to have been mentioned in any study. But there were some negative reactions mentioned in some studies that were missed by the pbi article... occasional incidents of stomach upset, allergic reaction, and vertigo. Also my own pubmed search
indicates it might also be a telomerase inhibitor... which might be a good thing for cancer patients.
I think the pbi article is mostly an argument of, "If it isn't broke, don't fix it." Which isn't totally off the wall. But would be more convincing without the unfounded scare tactics.
But to answer your question, I take Milk Thistle myself and have not experienced any negative effects. But I cycle it so I don't take it during weeks I take telomerase activating supplements like Astragalus out of concern it might interfere with them.