leech

Any of various chiefly aquatic carnivorous or bloodsucking annelid worms of the class (or subclass) Hirudinea, of which one species (Hirudo medicinalis) was formerly widely used by physicians for therapeutic bloodletting.

One that preys on or clings to another; a parasite.

A physician.

To bleed with leeches.

To drain the essence or exhaust the resources of.