Found some information on Milk Thistle here, if anyone is interested. You may find the comments to the article helpful as well. Excerpt from article below http://skeptvet.com/Blog/2011/04/milk-thistle-in-dogs-and-cats/
As far as risks, there appear to be few. Nausea, diarrhea, and other gastrointestinal effects are sometimes seen, and allergic reactions have been reported in humans.
So overall, the in vitro and laboratory animal evidence indicates it is plausible that milk thistle extract might have beneficial effects, though harmful effects in some situations could be expected as well. In humans, the clinical trials show weak evidence for benefit in diabetics and inconsistent but generally negative evidence for benefit in alcoholic or hepatitis-associated liver disease. Very little experimental, and apparently no high quality or controlled clinical research exists in dogs and cats. What there is suggests a benefit is possible. But we must bear in mind that preliminary, low-quality trials of milk thistle in humans looked promising but were not supported by subsequent better quality trials.
