The THC content in the blood is a misleading measure to determine a driver's "noise"


Measurement of intoxication can be performed very easily. The more you drink, the higher the alcohol content in the blood, and the more the person is intoxicated and is somewhere between "jingle" and "totally poured." On the other hand, measuring the degree of "noise" is currently quite unclear.

According to a study by the AAA Foundation for Traffic Safety (AAA), a non-profit organization dedicated to road safety in the United States (similar to our BESIP), blood tests used to determine marijuana use are virtually unusable to assess how much a driver is under under its influence. In other words, the study argues that a person with a low content of THC in the blood may behave as "stubbornly" as a person with a significantly higher level of THC, which may not even show any consequences of intoxication at all.

This finding is very serious, given that several US states have already adopted legal limits on the level of THC in the blood of drivers. The AAA concluded that such limits are "arbitrarily set without any support from the professional community, which may result in some motorists escaping punishment and others being wrongly charged."

For the purposes of this study, AAA researchers reviewed records of cases of driving under the influence of addictive substances, as well as results from toxicological analyzes and tests. These tests also included physical tests of the individual's intoxication (eg walking on a straight line, standing on one leg and touching with the index finger on the nose).

The researchers compared the results of 602 drivers who had only THC in their blood at the time of the arrest with the results of 349 volunteers who were sober and did not use any other drugs. The researchers first confirmed that "tested" drivers performed worse in tests than sober ones. For example, 55.5 percent of sober people passed the gait test with perfect results, while among those under the influence of marijuana it was only 6 percent.

The researchers then focused on the relationship between the results in these tests and the level of THC in the blood of the test subjects. In 602 "tested" drivers, the level of THC in the blood was between 1 and 47 nanograms per milliliter of blood, and while the level of THC in the blood probably affected the error in the index finger test, such tests did not show such a connection.


Similar results were obtained when researchers took a closer look at the association between error and THC levels above / below 5 ng / ml, a legal limit in several US states (eg, Colorado, Washington, and Montana). Even in this case, no clear differences were observed.

The authors mention that of the drivers who did not pass the sobriety test, 80 % people had blood THC levels of 1 ng / ml or higher. However, of those who passed the tests, 30 percent also had a THC level of 1 ng / ml or higher. The researchers conclude that based on this analysis, the quantitative limit for THC in laws and regulations cannot be scientifically supported.

In conclusion, it is also mentioned that other scientific teams also did not find any connection between the level of THC in the blood and the reduced ability to drive. One reason may be that THC is rapidly metabolised and its presence in the user's blood may depend on both the dose used and the frequency and regularity of marijuana use. In irregular marijuana smokers, the level of THC in the blood decreases rapidly, while in regular users, its level may remain higher for a longer period of time.

Nevertheless, people need to be discouraged from driving under the influence of marijuana. AAA claims that smoking marijuana affects the ability to drive. In a separate study, researchers found that in Washington state, the percentage of drivers who smoked marijuana before driving and were involved in a fatal accident rose from 8 percent in 2013 to 17 percent in 2014. The state legalized medical marijuana use in 2012. However, it must be borne in mind that most of these drivers had more than one type of drug in their body and also that the total number of road accidents had increased.

However, representatives of the organization called the increase alarming. They therefore recommend that, until the results of further scientific research are known, the police use a combination of behavioral tests and a mental state to determine whether a driver is able to drive safely after using marijuana.

You can meet roadside inspection at any time (photo source: