How exactly does this work? I tried it while poisoned and got the echos about the leeches taking most of the bad blood away, but nothing happened to the poison in my affects list. The poison was from a fillet - maybe too high level?

Thanks.

In most cases, the poison duration will go down, and the poison will become weaker (easier to cure / does less damage).

It's possible for that not to happen, though, and it's way more common with poison that's a lot lot higher level than you are -- so, yeah, a filet poison when you're not that high level probably counts.