Although in the same family ( Asteraceae, previously known as Compositae - commonly Daisy family ), blessed thistle and milk thistle are different species. blessed thistle ( holy thistle, our lady's thistle ) is Cnicus benedictus L. (synonym/formerly Carduus benedictus). milk thistle is Silybum marianum ( synonym/formerly Carduus marianum) Rosemary Gladstar has nice things to say about both of them. Seems the taxonomists are the ones most invested in distinguishing between the two. Bingel and Farnsworth list both as lactogogues, although blessed thistle has bigger/more specific reputation. Most research done on milk thistle regards support/restoration of liver cell function. Used in Europe for Amanita poisonings - saves lives. Both species contain physiologically active compounds thay assist liver function and which also may be relatable to lactation ( if someone would do the research here!). Sheila Humphrey BSc RN IBCLC [log in to unmask]