Alcohol and cannabis are the most commonly used substances among adults and teenagers in the U.S. and other developed countries. One survey showed that 41, 62 and 73% of Year 8, 10 and 12 students respectively had drunk alcohol with the figures for cannabis smoking for the same years being 16, 32 and 42%. Many programmes for preventing teenage alcohol and drug use aim to delay the age at which people first start using these substances with the hope that this will prevent problems in adolescence and adulthood. However, few long-term studies have followed people from early adolescence to young adulthood in order to examine the effects of early drug and alcohol use. Researchers from Weill Cornell Medical College in New York followed 621 people from Year 7 to Year 12 asking them about their drug and alcohol use and then got them to fill out a survey about their lives at 24. The study found that an early start to substance use was linked to a higher incidence of weekly alcohol use in young adulthood as well as more substance-related occupational,relationship and legal problems. The majority of young adults with problems due to alcohol or drug use had first reported having alcohol and cannabis before Year 12. The negative effects of early-onset substance use were strongest in people's social and work lives.
Griffin, K.W., Bang, H. and Botvin, G.J. - Age of alcohol and marijuana use onset predicts weekly substance use and related psychosocial problems during young adulthood. Journal of Substance Use, June 2010, 15(3), 174-183