Study: Blood and oral fluid THC concentration does not prove impairment

Published Dec 28, 2021 10:00 a.m. ET
iStock / anyaberkut

There’s been a lot of debate on the subject of cannabis intoxication as of late since governments and regulatory agencies have set to work to figure out how to detect the newly legal substance choice in a manner that is both consistent and fair. Sadly, we’ve seen very little progress in this department, as researchers struggle to understand how to determine whether or not someone is impaired based on blood, urine, or saliva THC concentration alone.

New research confirms why this has been so challenging, pointing to a need for alternative drug test options that do not operate on the same premise as those we use to identify alcohol intoxication.

Testing for alcohol impairment

When officers pull over someone who is suspected of impaired driving due to alcohol, the process is incredibly straightforward and easy to understand. With a breathalyzer or drug test, it doesn’t take long for them to figure out whether or not those suspicions are true, and it all comes down to the amount of alcohol that’s found in the suspected individuals’ system.

Over a certain point and they’re too drunk to be out on the roads. Under a certain amount and they’re free to go home, but with cannabis, it’s so much more complicated than that because cannabinoids or at least indications of their presence can be found through oral fluid tests long after the effects have worn off.

The study

There is a much stronger relationship between alcohol concentrations found in the blood or breath and intoxication, but researchers from the University of Sydney’s Lambert initiative looked at data to see if they could find a similar link to cannabis and impaired driving, and just as we thought, the connection is unreliable at best.

The results of this study revealed that THC concentration is a poor way to determine whether or not a person is in a safe state of mind to get behind the wheel of a motor vehicle. According to the lead authors’ notes, there is “no significant relationship” detected among cannabis consumers, a fact determined by assessing true impairment versus perceived intoxication based on statistics gathered through many years of study.

What's most interesting is that this research seems to indicate that those with high concentrations of THC might not be impaired, while those who aren’t even registering are likely due to recent use that hasn’t been completely processed by the body. So not only can these types of tests provide false positives, but they’re also entirely likely to produce a false negative, which would allow an individual who shouldn’t be behind the wheel to go free.

If we can’t rely on blood or oral fluid drug test options, is there another way?

The truth is that we’ve yet to standardize any proven method of testing a person for being under the influence of cannabis, though there are some prototypes showing promise for the future. However, some say that all of this effort is for nothing, as it’s been proven that smoking, which is the most common method of cannabis use, only impacts an individual's ability to react and drive for approximately 30 minutes.

Whether or not it’s necessary is debatable, and with an evolving answer, that might change as edibles and beverages become more widely used. Either way, it’s good to know that these faulty tests have no legal leg to stand on, thanks to science.

No increase in impaired driving rates since marijuana legalization


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