In Fantastic Beasts (the textbook) we find this:
The werewolf is found worldwide, though it is believed to have originated in northern Europe. Humans turn into werewolves only when bitten. There is no known cure, though recent developments in potion-making have to a great extent alleviated the worst symptoms. Once a month, at the full moon, the otherwise sane and normal wizard or Muggle afflicted transforms into a murderous beast. Almost uniquely among fantastic creatures, the werewolf actively seeks humans in preference to any other kind of prey.
However, in Prisoner of Azkaban, Lupin says:
I as a very small boy when I received the bite. My parents tried everything, but in those days there was no cure.
Although that could possibly be referring to the Potion, which is referenced in the next sentence.
However, in Sorcerer's Stone, Harry and Hermione learn about cures for werewolf bites:
The next morning in Defense Against the Dark Arts, while copying down different ways of treating werewolf bites, Harry and Ron were still discussing what they'd do with a Sorcerer's Stone if they had one.
Which implies that there is a not only a treatment, but multiple treatments! Or is that referring to the potion as well?