Coffee isn't good either. Probably a lot less bad than weed, though. And it's always brought up, "why is X illegal but coffee isn't?"
I'm pretty convinced that caffeine masked the more obvious symptoms of sleep apnea for most of my adult life. I think I was getting very bad sleep but since I had always drunk lots of Diet Coke I was able to ignore the symptoms.
I've gotten treatment for my sleep apnea (using the mouthpiece), and I'm caffeine free now, so I think I'm getting better sleep, but who the hell knows what kind of brain damage I have ended up with because I didn't take it seriously.