Wade Davis's 1985 Book - The Serpent + the Rainbow
I think this is a great film, well made from the book The Serpent & the Rainbow, I mean it's not word for word from the book but the story is basically the same ... Harvard scientist is commissioned to look for the drugs (poison and antidote) for Zombification. He stumbles in to a secret Haitian voodoo society, while finding out about Zombis and Magic.
http://www.wade-davis.com
this is a Zombies true voodoo roots ... and it's not the same as those other Dead films, which I think are not Zombies but are a type of Ghoul.