If you want to avoid a car crash, trade a joint for that glass of wine. A study from the National Highway Traffic Safety Administration (NHTSA) found that drivers who used marijuana were at a significantly lower risk for a crash than drivers who used alcohol. After adjusting for age, gender, race and alcohol use, drivers with marijuana in their system were at about the same level of accident risk as those who had not used any drugs or alcohol prior to driving. Apparently, weed and driving are okay.
Interestingly enough antidepressants, pain killers, stimulants and quite a few other legal and illegal drugs do not significantly increase the risk of being in a crash. Alcohol use greatly increases the likelihood of an accident even at modest blood concentrations. In fact, a blood alcohol concentration over 0.05 increases your odds of a wreck nearly seven fold.
The study’s findings underscore an important point: The measurable presence of THC (marijuana’s primary active ingredient) in a person’s system doesn’t correlate with impairment in the same way that blood alcohol concentration does.
The NHTSA study points out that “At the current time, specific drug concentration levels cannot be reliably equated with a specific degree of driver impairment.” There are many reasons why detectable drug presence doesn’t indicate impairment the way it does with alcohol. Most psychoactive drugs are chemically complex molecules whose absorption, action and elimination from the body are difficult to predict. Also, there are considerable differences that exist between individuals with regard to the rates with which these processes occur. Alcohol is more predictable. In heavy marijuana users, measurable amount of THC can be detected in the body days and even weeks after the last use, and long after any psychoactive effects remain. Washington Initiative 502, passed in 2012, set a legal limit at which the driver is automatically determined to be impaired at 5 of nanograms of active THC per milliliter of blood. However, this number tells us nothing about whether a person is impaired or fit to drive.