Cannabis and the Risk of Crash Involvement

Drugs have long been a focus of law enforcement in Australia but recent legislation in a number of Australian states now requires routine drug testing of drivers (testing for cannabis and methamphetamine), with the stated aim of reducing road crashes. Such legislation is justified if these drugs are known to increase the risk of crashing. Literature concerning cannabis and road crash involvement was reviewed, with emphasis given to studies documenting the relative crash risk associated with driving after use of cannabis. All case-control and culpability studies of cannabis and crashes have been characterised by methodological flaws that make interpretation of the results difficult. Two recent Australian studies analysed the relationship between tetrahydrocannabinol (THC, the psychoactive component of cannabis) measured in the blood and crash culpability. These two studies produced contradictory results. In summary, the risk of crash involvement associated with driving under the influence of cannabis remains to be determined.