Although some very weird ingredients went into potions in those days, snake venom was not one of them... or, at least, if it was, it wasn't in wide usage.

It is true, however, that there would be one or more holy snakes living in temples sacred to Asclepius. The Athenian tragedian Sophocles (author of Oedipus the King) once took an Asclepian snake into his own household during the time of the great plague in Athens, while the first sanctuary to Asclepius was being built in the city. For this service--and not for his tragedies--he was worshipped as a cult hero after death. He was given the title of "Sophocles Dexion," which means "Sophocles the Receiver."

Sometimes patients in the Asclepius sanctuaries reported dreams in which Asclepius's snakes licked or sucked their wounds to cure them. Eeeeew!