Cannabis increase the risk of crash. A case-control study in
france had proved it. However it is much lower risk than people associated with
positive blood alcohol concentration. In the study, a Positive detection of
cannabis mean delta tetrahydrocannabinol of over 1 ng/ml. The result was from
9772 drivers, 7.0% were positive cannabis, 21.4% were positive of alcohol, and
2.9% were positive for both. Men are more often involve in crash. Men are also
more often detected positive for cannabis and alcohol than woman (Laumon et
al., 2005). Another study about cannabis had found that the significance
dose-response indicates the relationship between cannabis and road crash.
Laslty, there is a multiplicative effect between cannabis and alcohol
(Gadegbeku et al., 2011).