Not all "hard" drugs are addictive. Shrooms and LSD are both pretty much not addictive. Even cocaine, which I've done a fair amount of, isn't addictive to me. Some people seem to get addicted to it pretty easily, but I've never found myself jonesing to get some. I think as long as you don't fuck with heroin, crack, or meth, you are pretty much in the clear as far as addictiveness goes. I've even had friends that could smoke crack on occasion and not even get close to being addicted to it. I've never risked trying it myself, though.

Oh, and lots of prescription drugs are addictive as well. I wouldn't fuck with most of them if you are worried about getting addicted. But hallucinogens in general are safe as far as that goes, and I think they positively impact most people that do them, especially if done in the right environment with the right people.