I think that milk thistle isn’t terribly water soluble. So probably the most effective ways are to take the whole herb or a full-spectrum extract in both water and alcohol (a tincture). There are plenty of encapsulated products. They are all going to be way over-priced. Same with tinctures – overpriced. But they are convenient. A more economical, though less convenient approach is to grind the whole seed. A coffee grinder will work well for this. You’d need to grind it fresh – otherwise it will oxidize.
So bottom line is either whole (ground) seed or tincture is going to be more effective than water extract (tea). Grind it yourself for economics. Or, for convenience, buy encapsulated or tinctured herbs. Personally, I prefer whole spectrum extracts or whole herbs versus standardized extracts since they may well be guessing incorrectly at the “active ingredients”.
Just my two cents.