Objective: We explored among people who ever consumed alcohol whether early age at drinking onset and alcohol dependence predicted drug use and dependence. We also examined among drinkers who have used drugs whether they also predict driving under the influence of drugs and motor-vehicle crash involvement because of drugs.
Method: A U.S. national sample of 42,867 persons age 18 and older was surveyed in 1991-1992 (response rate = 90%). Logistic regression examined these potential associations among 27,616 respondents who ever drank alcohol, controlling for numerous demographic and personal characteristics.
Results: Among "ever" drinkers, 22% used drugs, 10% had driven under the influence of drugs, and nearly 1% was in a motor-vehicle crash because of drug use, the equivalent of 1 million people. The younger the age of respondents when they first began drinking and whether they ever experienced alcohol dependence were independently associated with greater odds of ever using drugs and experiencing drug dependence. Among persons who consumed alcohol and drugs, having ever experienced drug dependence was the strongest predictor of driving under the influence of drugs and motor-vehicle crash involvement because of drug use. After controlling for drug dependence and age at first drug use, having experienced alcohol dependence was also independently associated with both outcomes.
Conclusions: Efforts to prevent drug-related crashes should include drug use prevention and treatment, as well as prevention of early alcohol use and treatment of alcohol dependence.