Painkillers are serious drugs that are ridiculously easy to become addicted to. Not just mentally, but physically, as well.
But there's a reason people take them: because they work. I mean, I don't know if you've ever been unfortunate enough to need painkillers, but if you have, you know just how potent they can be.
And different people have different reactions to painkillers. We all remember that kid who went to the dentist and questioned the nature of existence, right?