Drugs? People do so much to get to them, but very few bother figuring out what they do. Meth will make you look years older, your teeth will rot and your hair will begin to fall out.
Alcohol? It is not as bad as smoking and drugs. Although when you sit there and drink and drink you will become an alcoholic. Most people don't realize there addicted till its to late. But even if you do realize it early enough it still may be hard to quit.
Smoking? You will regret the day you picked it up. You can smoke all you want, but soon you'll realize its not keeping you calmer anymore. Its making you more anxious, except now all you want is a cigarette.