Marijuana and Driving: What You Should Know Marijuana 101 - Part 2

Studies show it is not safe to drive while high. You should wait 4 hours after smoking before driving.

Driving high is a form of impaired driving. Your ability to drive safely can be significantly affected after using marijuana.

Impaired driving is the leading cause of both injury and death in North America. In Canada, there is a drug-impaired driving offence every 3 hours.

Many people believe using marijuana or other drugs isn't as bad as driving drunk. But in 2010, almost as many drivers died in road crashes after using drugs (34%) as those caused by drinking and driving (39%).

So before you get behind the wheel or get into a car with another driver, it's important to understand the effects of marijuana on driving.

What are the dangers of mixing marijuana and alcohol?

One study looked at how driving skills are affected by marijuana or alcohol, and their combined effects on driving. Subjects were given various doses of marijuana with or without alcohol and tested in normal traffic.

When low doses of THC were given, there was a moderate impairment. But when THC was combined with even a low dose of alcohol - a common scenario at parties - driving performance was severely affected.

How Do I Know If I'm Impaired?

Marijuana impairs the ability to drive by affecting your coordination, attention, judgement, reaction time and decision-making skills.

Most studies show that using marijuana impairs your mental functioning when it comes to "cognitive" or thinking ability and short-term memory tasks.

Signs of marijuana impairment include:

Red or bloodshot eyes

Delayed reaction time

Distorted sense of your surroundings

Poor coordination

Feeling anxious or panicky

Feeling dizzy or tired

What should I do if I'm impaired?

If you are impaired, don't get behind the wheel. If somebody you know is impaired, refuse to drive with them. Try to find something to do until the high wears off (approximately 4 hours after smoking).

Being under the influence of marijuana means that your ability to react appropriately in any given situation while driving may be significantly affected. A split-second decision could mean the difference between life and death.

Does marijuana always cause driving impairment?

Some people erroneously believe that marijuana makes you a better driver, because you're more cautious. Even if you feel like you are being cautious, your reaction time and other driving skills are impaired by marijuana.

Some people may also believe that it is safe to drive while high if you have a tolerance. But don't be fooled. Marijuana can still make it dangerous to drive even if you are a seasoned user.

How Is Marijuana Detected in Drivers?

Marijuana-impaired driving is something you can be charged with, but law enforcement officers often have problems detecting whether or not a driver is under the influence.

Right now, police use roadside behavioral testing for marijuana use. They may also run a blood or urine test to verify that marijuana was taken, but these tests have poor time resolution and can't always indicate exactly when the driver was impaired.

Is there a marijuana breathalyzer?

There is currently no "breathalyzer"-type test for marijuana as there is for alcohol. However, there are several devices that are currently under development, including the use of a roadside saliva swab.

What happens when you are pulled over?

If you are pulled over, police will do a visual inspection, and may see if they can detect the scent of marijuana in the car.

If police suspect that you are high, you can be asked to do a standardized sobriety test on site or at the police station. These tests usually consist of an evaluation of your eyes (red or dilated) and coordination challenges. Police can also request a drug test.