How do you kill a werewolf in Supernatural?

Why silver, and why the heart?

Silver is the oldest rule in werewolf fiction, and Supernatural keeps it, then adds a target. Silver hurts a werewolf on contact, but the killing shot is the one that reaches the heart, so a familiar weapon becomes a matter of skill and nerve: the hunter has to land one blow on something fast, strong and frantic, often in the dark, with no second chance if the first goes wide.

There is a symmetry in it the show leaves unspoken. Its werewolves kill by tearing out human hearts, and the surest way to stop them is to strike their own. The heart is both what the monster wants and where it is weakest. The later seasons even test the rule: werewolves strengthened with an archangel's grace shrug off silver entirely, and only taking the head stops them, which tells you how much the show expects silver to carry.

What separates bitten werewolves from purebloods?

Control. A bitten werewolf was a person until another werewolf's bite in its changed form passed the condition on. They turn at the height of the lunar cycle, usually in their sleep, remember little of it afterwards, and go hunting for human hearts while they are turned. Purebloods are those closest to the first werewolf, up to the fourth generation of descent; they change whenever they choose, keep their memories, and can live on animal hearts rather than human ones.

That split lets the series ask one of its favourite questions: can a monster choose not to be one? A pureblood living on animal hearts is, by the show's own logic, not a killer at all, and the brothers have always said they hunt things that hurt people. The pureblood stories push hard on that code, and the show admits it costs them: a taste of a human heart makes the next one harder to refuse.

Can a werewolf in the show be cured?

Only early, and only after a long wait. The first werewolf story the series tells tests an old belief, that killing the werewolf who did the biting frees the person bitten, and lets it fail. For most of the run a bite is effectively a sentence. Much later the British Men of Letters produce a real cure: an injection made from the blood of the werewolf who did the biting, drawn while it still lives, which works only in the early stages and, like the vampire cure, not at all once the werewolf has fed.

Even then the show keeps the price visible. The cure is painful enough that not everyone it is tried on survives it, and it arrives with the cold efficiency that makes that organisation so unsettling to the brothers. What it changes is the question every werewolf story was really asking. If a cure exists, killing a bitten person stops being the only answer, and a hunter has to weigh speed against mercy in a way the early seasons never demanded.

Where do werewolves come from in the show's mythology?

Like vampires, they come from a single ancestor. The show's werewolves descend from an Alpha Werewolf, and behind the Alpha stands Eve, the mother of all monsters, whom season 6 makes the origin of the monster families. That history explains why purebloods matter so much: they are the line nearest the source. The vampires have a family tree of exactly the same shape, which is the point of building one.

One werewolf story stands apart because it happens to a hunter. Garth Fitzgerald IV, a friend of the brothers, was bitten while hunting a werewolf, and when he comes back in season 9, episode 12 he has become one himself, married into a pack and living off animals rather than people. He is the series' most sympathetic werewolf, and the clearest test of whether the brothers' rules can bend for someone they know.