Does Marijuana Impair Driving?

Driving under the influence of marijuana is dangerous and illegal. The effects of driving while high are similar to those of driving while drunk. Getting behind the wheel after smoking or using marijuana in any other way can be dangerous for you and for everyone else on the road. Driving while high should be avoided at all costs.

Studies have found that, after testing the blood of drivers involved in car crashes, marijuana is the drug detected most often. Studies have also found that drivers with THC in their bloodstream are more than twice as likely to be at fault for fatal car crashes than sober drivers.

Unfortunately, according to the United States National Highway Traffic Safety Administration, driving while under the influence of marijuana may be on the rise. Among drivers surveyed at night and on the weekend, 12.6 per cent had THC in their system. Only 8.7 per cent tested positive for THC in 2007. This is concerning when compared to the rates of driving while drunk, which are declining.

A study by the United States National Institute on Drug Abuse examined the effects of marijuana on driving and compared those to the effects of alcohol. They focused on weaving within a road lane, leaving the lane, and how fast the car was weaving. They found that alcohol decreased a persons driving ability according to all three measurements. Marijuana caused drivers to weave more, but did not affect how quickly or how many times their car left their lane.

The study also found that marijuana and alcohol affect driving even more when used together. Alcohol increases a person’s ability to absorb THC, which makes the high more intense (and decreases the person’s ability to drive more than marijuana or alcohol alone). Drivers who used small amounts of marijuana and alcohol were found to weave more in their lanes, even if they were under the legal limit for both substances. THC also caused a delay in the peak effect of alcohol. This could lead people to believe that they are not as drunk as they truly are. They might then choose to drive and start feeling the full effects of alcohol after they are already on the road. People should avoid driving under the influence at all times, but especially if they have consumed both alcohol and marijuana.

The legal blood alcohol limit for drivers is .08 per cent. It is very difficult to establish a comparable limit for marijuana for several reasons. The first is that blood cannot easily be checked for marijuana on the side of the road. Tests are often done hours after the impaired driver’s arrest, meaning that the level of THC in their blood will have dropped considerably. Another issue is that marijuana affects everyone differently, and that tolerances vary wildly. Moreover, marijuana can be detected in the blood for weeks after the drug was used.