"Substance abuse is typically defined as the use of alcohol or other drugs in ways that negatively affect life functions. These negative effects can be legal (e.g., arrests), physical (e.g., injuries), emotional (e.g., irritability), or behavioral (e.g., truancy, impaired academic performance, auto accidents, risky sex, violence, or delinquency). Most adolescents who use alcohol and drugs do not use them in ways that are considered abuse. Use that begins at an earlier than average age, however, increases the probability that use will escalate into abuse. Furthermore, use by children and adolescents at any age places them at greater risk for negative consequences than does abstinence."
from: Substance Abuse
by Susan G. Forman, Brenna H. Bry, and Phuong-Anh Urga
Drug and Alcohol Abuse-has many links for specific drugs