In the southernmost reaches of the southernmost lands, among sun-baked golden hills and rocky ruins, the cities of Gor Kull offer travelers and citizens a plethora of sinful concoctions, powders, and draughts, born of a wicked desire to addle the mind and befuddle the eye. Yet, should ye wish to arm oneself with knowledge against such evil brews, I present such guide.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.