19Silver Won't Actually Hurt Him
Just like how vampires can't stand garlic, or how mummies are afraid of cats, in literature, a werewolf's greatest weakness is silver. The idea seems to date back to 18th century folklore called The Legend of the Beast of Gevaudan. However, some suggest that 19th Century authors went back and
altered that telling. Regardless, silver being the thing that ends werewolves has become a staple of all literature.
This is not the case in J.K. Rowling's Harry Potter franchise. At no point does Rowling state that silver can actually harm Lupin in any way. In fact, there's much reason to believe that the metal would do nothing to him. After all, he's often surrounded by various silver artifacts, including in his Defense Against the Dark Arts classroom.