Driving after smoking marijuana may double your risk of an accident.

That's coming from a new study Friday morning published in the British Medical Journal.

Canadian researchers looked at several other studies involving nearly 50,000 people. They found that drivers who used pot within three hours of getting behind the wheel were almost twice as likely to cause a car accident.

Alcohol impairs drivers' speed and reaction time, while cannabis affects spatial location, said Mark Asbridge, associate professor in the Department of Community Health and Epidemiology at Dalhousie University in Halifax, Nova Scotia, told CNN.

According to the National Institute of Drug Abuse, marijuana is the most prevalent illegal drug found in impaired drivers, fatally injured drivers, and crash victims.

The effects of marijuana don't last nearly as long as alcohol; pot wears off within a few hours, while alcohol could impair a driver's ability for as much as 12 hours depending on how much was consumed.

Previous studies show the risk of an accident is even higher if the driver is 35 years old or higher.

They say drivers high on marijuana may follow cars too close, and swerve in and out of lanes.

Unlike alcohol levels, studies have been unable to make clear what level of pot would need to be consumed in order to cause impairment.