I thought it was common knowledge that a lot of analgesics contain caffeine? It's the because it can increase absorption / efficacy, and is a pretty effective analgesic itself.
I rely on High5 Zero Plus caffeine tabs. 4 of them, and your hangover is deferred for a few hours. It's still there, ready to pounce, but it gives you a few hours breathing space.
May well be. News to me though!