In other cases the transformation was supposed to be accomplished by Satanic agency voluntarily submitted to, and that for the most loathsome ends, in particular for the gratification of a craving for human flesh.
"The werewolves," writes Richard Verstegan (Restitution of Decayed Intelligence, 1628), "are certayne sorcerers, who having annoynted their bodies with an oyntment which they make by the instinct of the devil, and putting on a certayne inchaunted girdle, doe not onely unto the view of others seeme as wolves, but to their owne thinking have both the shape and nature of wolves, so long as they weare the said girdle. And they do dispose themselves as very wolves, in wourrying and killing, and most of humane creatures."
Such were the views about lycanthropy current throughout the continent of Europe when Verstegan wrote. The ointments and salves in question may have contained hallucinogenic agents.
It is said that humans who enter into a pact with the Devil himself do so out of desperation and often, in an effort to seek revenge for the death of a loved one.
In popular European superstition, the Devil is said to appear in the form of a coachman whose carriage is drawn by black steeds. The Devil offers a potion that provides the strength needed to carry out the revenge, in exchange for the person's soul. The potion is often in the form of a vial, the contents of which are applied to the human skin under the light of a full moon. The transformation into a werewolf will then begin immediately and the human has been completely turned into a werewolf forever.
More about demons and the Devil.
How to become a werewolf