BBC News 10 Feb 2012
Drivers who use cannabis up to three hours before driving are twice as likely to cause a collision as those not under the influence of drugs or alcohol, says a Canadian study.
This is because cannabis impairs brain and motor functions needed for safe driving, the researchers suggest.
The study in bmj.com reviewed nine studies of 50,000 people worldwide who had been in serious or fatal crashes. Experts support the close monitoring of serious accidents involving drugs.
The study analysis was carried out by researchers at Dalhousie University in Halifax, Canada.