A survey of 27,616 people in the U.S. looked into the links between the age at which people first started drinking, alcohol dependence, drug taking and driving under the influence of drink or drugs. All the sample were drinkers. 22% of the sample had used drugs, 10% had driven under the influence of drugs and 1% had been in a crash because of their drug use. Starting to drink at a young age and being alcohol-dependent were both associated with an increased risk of using drugs and becoming drug-dependent. Being drug and alcohol-dependent were both associated with an increased risk of driving under the influence of drugs and being involved in a drug-related accident.
Hingson, Ralph W., Heeren, Timothy and Edwards, Erika M. - Age at drinking onset, alcohol dependence, and their relation to drug use and dependence, driving under the influence of drugs, and motor-vehicle crash involvement because of drugs Journal of Studies on Alcohol and Drugs March 2008, 69(2), 192-201