BACKGROUND: Alcohol is known to be associated with injury, but little is known of combined use of alcohol and other drugs on injury; especially important for marijuana, given increasing legalization of use in the U.S. and Canada.
METHODS: Probability samples of patients 18 and older were interviewed in the emergency department at two sites in Vancouver and one in Victoria, BC (n=1191 injured and 1613 non-injured patients). Case-control and case-crossover analyses were used to analyze risk of injury, based on self-reported alcohol and drug use (marijuana, stimulants, depressants) prior to injury.
RESULTS: Risk of injury was significantly elevated (p<0.001) for alcohol use alone in both case-control (OR=2.72) and case-crossover analyses (OR=2.80) but not for any of the three drug classes. The interaction of alcohol with each class of drug was tested, and marginally significant only for marijuana in case-control analysis (OR=4.42; p=0.088). The interaction of alcohol and two or more drugs was also significant in case-control analysis (OR=03; p=0.035). The volume of alcohol consumed prior to injury was greater for those also using drugs during this time and positively associated with the number of drugs reported.
CONCLUSION: Given the potential issues involved with both case-control and case-crossover study designs, the inconsistent findings suggest caution in reaching any definite conclusion regarding whether there is extra risk related to combined use of alcohol and marijuana, and is an important area for future research.