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
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