The few times I tried it, I felt really awesome for about 10 minutes, then suffered terrible anxiety and insomnia for at least a week. I've spoken to several other people who've had a similar experience with it.
Those are pretty negative effects, in my opinion, but maybe you mean permanent, physical damage, or something like that?
Some people do have anxiety, and I agree that it's extremely negative, but a lot of people don't. (I do get panicky, which is why I don't smoke, but my friends don't).
My whole point is that if you do get too anxious and freak out with it, DON'T DO IT! Lots of people don't get those effects, and would like those who do to stay out of their business!
Those are pretty negative effects, in my opinion, but maybe you mean permanent, physical damage, or something like that?