Saliva roadside drug tests for THC are disturbingly ineffective

Published May 1, 2021 09:00 a.m. ET
iStock / zoka74

Now that cannabis is legal in so many places, experts are racing to figure out how to prevent any problems that might arise. One of the biggest concerns surrounding legalization was the potential for this shift to increase the number of impaired drivers on public streets, and though it doesn’t seem like improving access has increased the number of people who are getting behind the wheel under the influence of a substance, experts and officials are racing to figure out how to police drivers who use cannabis.

Why this is a concern

We don’t have much evidence to suggest that there is a substantial number of drivers who pose danger due to cannabis. Still, it is a fear for those who are against this shift in legislation, as well as law enforcement, who see first-hand the damage that can be caused by impaired drivers. As a result, they want a reliable and consistent way to determine whether or not a person has recently consumed cannabis, a task that’s much harder than it sounds.

The current roadside drug test protocol

Right now, determining how high a driver might be is a different process depending on where you look, with each region instilling its own rules designed to catch behaviors, cues, and evidence of impairment. However, they all rely on the same general tests to prove things like sobriety (or a lack thereof) in a court of law. Physical sobriety tests, like the infamous walk the line, where a driver is expected to confidently stride down a straight line, but this alone is not enough to determine impairment.

The next line of defense is usually the saliva test, which can be administered on the roadside with a small cotton swab and a few moments of time. This drug test is used in most countries and states to look for cannabis in a person’s saliva, but the unfortunate truth is that they really aren’t accurate enough to rely on, which can lead to a host of issues.


How effective is a saliva drug test for THC?

According to a recent study conducted in Michigan, the saliva drug test isn’t good for anyone. Out of 943 positive results in this test, a staggering 11% came back as either a false positive or false negative, determined by a follow-up blood test and toxicology report, that’s 222 wrong results. Of course, not all of these tests found cannabis, as they were looking for all possible drugs, but this is proof of how ineffective a roadside saliva test really is.

Isn’t anything better than nothing?

For now, the saliva drug test will continue to be used by law enforcement agencies around the world, that is until we find a better way, but while we wait, this is a serious issue that will leave innocent people to suffer. 222 wrong results out of less than 1,000 tests translate to 222 innocent drivers who were detained and forced to submit blood testing to prove that they never did anything wrong—a huge waste of time and resources. So, while it’s good to know we have something, it might not really be that much better than nothing.

What you should know about cannabis drug testing


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