Illegal drugs aren't good for anyone, but they are particularly bad for a kid or teen whose body is still growing. Illegal drugs can damage the brain, heart, and other important organs. Cocaine, for instance, can cause a heart attack — even in a kid or teen.
While using drugs, people are also less able to do well in school, sports, and other activities. It's often harder to think clearly and make good decisions. People can do dumb or dangerous things that could hurt them — or other people — when they use drugs.(http://kidshealth.org/kid/grow/drugs_alcohol/know_drugs.html)