There's lots of room for more contributions on this, but you may be interested in these posts
Sunday AMA: I am FG_SF, ask me questions about the history of science & medicine!
How common was the medical use of leeches in the Middle Ages? Where did it come from? How did the practice disappear?
Was premodern medicine, (e.g. Bleeding, Mercury, leeching) ever effective against disease? If not why did medieval doctors continue to use these techniques?
How efficient/effective was ancient and medieval medicine?
What things did Medieval European medicine get right?
Is there any medical practice from medieval or ancient times that has remained mostly unchanged after all these years?
Cauterization in the ancient/medieval world
Was medicine distributed and prescribed by apothecaries in Medieval/Renaissance Europe effective at all?