Substance use is linked to the three leading causes of morbidity and mortality among youth in the United States - unintentional injury, homicide, and suicide.1-3 Heavy substance use during adolescence also is associated with substance use problems during adulthood.4, 5 In addition, research suggests that adolescents who have an early onset of alcohol use are more likely to drink heavily and to develop alcohol problems than those who initiate alcohol use later.6 The relationship between early substance use and later substance abuse problems may simply reflect an individual's genetic predisposition for the development of substance abuse.7,8 Numerous studies have shown that individuals with a genetic predisposition for substance abuse (e.g., offspring of alcoholic parents) have an increased risk for early substance use, heavy substance use, and alcohol and drug problems.9,10 Of note, this genetic predisposition may manifest differently during different developmental stages (e.g., early onset during adolescence, alcohol dependence during adulthood). Indeed, strong genetic effects have been found to contribute to both early drinking age of onset and to alcohol dependence.11,12
