''Drivers who consume cannabis within three hours of driving are nearly twice as likely to cause a vehicle collision as those who are not under the influence of drugs or alcohol claims a paper published today on bmj.com.
The paper's authors, from Dalhousie University, reviewed nine studies with a total sample of 49,411 people to determine whether the consumption of cannabis increases the risk of a motor vehicle collision''
http://www.bmj.com/press-releases/20...collision-risk