Nouns

(n)leech, bloodsucker, hirudineancarnivorous or bloodsucking aquatic or terrestrial worms typically having a sucker at each end
(n)leech, parasite, sponge, spongera follower who hangs around a host (without benefit to the host) in hope of gain or advantage

Verbs

(v)bleed, leech, phlebotomize, phlebotomisedraw blood“In the old days, doctors routinely bled patients as part of the treatment”