I remember reading in one of  Terence Mckenna's books that he speculated John Dee was the author of the Voynich Manuscript or at least an owner at one point.  I'm reading Chris Bennetts book about alchemy and cannabis and he is pretty sure that most of the elixirs of life were cannabis and opium tinctures, if you've studies Paracelsus and his writings it's fairly obvious opium and cannabis were used.