I think that peer pressure is a matter of a lack of self-control. Everyone is capable of controlling their actions and not sinking to other people's levels. It's easy to say 'NO' to something you don't want to do. If someone wants you to do something you don't want to do, you should re-evaluate your relationship between that person and consider whether you're better off without them in your life. In school we get told not to succumb to "peer pressure" by taunts of "Don't drink", "Don't smoke, "Don't do drugs" and many people don't succumb to the pressure. "Peer pressure" is a word created by the media to blame anti-social behavior on something rather than exposing the fact to our immoral society.
Fact is that many teenagers experiment with drugs and alcohol and they have done so for dozens of years and it won't change. Not many people do it out of "pressure" it's done out of choice. If we didn't experiment then we'd live in a world of sober people who have not touched a drop of the depressant.
At the end of the day everyone can say "NO" and not feel guilty of it.