From the research that I have carried out and also from the many books I have that carry information regarding Milk thistle, all suggest that there are no contra-indications for Milk thistle and that it is perfectly safe in its use apart from two.  Rudolf Weiss suggests that Milk thistle has become the plant extract of choice for liver conditions, he writes, "It can be given in acute stages of virus hepatitis and all chronic liver disorders including fatty liver.  The milk thistle is perfectly safe and therefore does not carry the risks of many other liver drugs." (30). 

            The two books that I do possess that indicate there may be contra-indications state that treatment with Milk thistle should be medically supervised.  They do not give any indication as to why this is the case.  The Illustrated Encyclopedia of Herbs states, "Treatment with Milk Thistle should be medically supervised." (31).  The other is Color Dictionary of Herbs and Herbalism which states, "The seed should be used only by medical personnel." (32).  From these two comments and understanding the use of Milk thistle I can only assume that they are suggesting treatment for the liver should only be carried out by medically qualified personnel.  In that there is no indication as to whether they mean doctors or Herbalists.