The attitudes about drugs are what parents and other adults have to combat. Sometimes you can't tell until a person is in recovery for a while. Usually a person who can maintain a state of recovery can tell you why they used drugs. Very often drug use is a symptom. Sometimes it's medical, including psychiatric.
Depression is a big factor.
If you're feeling low and blue many people will try cocaine. Cocaine use leads to REAL depression. Much worse than if the depression was left alone. The important thing is to get them off drugs and give them a place to attack their problems. Give them a place to be heard.