movie is loosely based on real life groups, characters, events and voodoo in haiti.
back in the 80s and early 90s, this guy was known to have been the only case of a documented zombie:
Clairvius Narcisse -
Clairvius Narcisse - Wikipedia, the free encyclopedia
the movie is about zombies in the classical sense - where the dead come out of the grave. back in the day in haiti, there was a paramilitary group that used to terrorize, kidnap and murder haitians. they used black magic and voodoo to scare muhfukkas by supposedly stealing souls.
this is where zombie potion comes from. i don't want to give spoilers, so you'll have to watch it.
but the "west" does have the drug now, that they took from practitioners that used to fukk with the rituals and shyt.
anyway, it's a good flick, the dude in the movie poster is bill pullman, if you didn't recognize him.