Cannabis in traffic

Cannabis am Steuer

Schmid: We are experiencing a mixture of arbitrariness and covert drug policy.

In Austria, there is an increase in driver’s license revocations due to cannabis use. New record highs in drug-related offenses while driving are being reported continuously. However, how many accidents are actually caused annually by cannabis consumption while driving? There is not a single study available on that topic. The distraction caused by using a phone while driving is well-researched; however, there is no existing data on cannabis. Professor Rainer Schmid, a toxicologist, suspects that a problem is being created here that wouldn’t exist if lawmakers could agree on introducing a permissible limit. Schmid headed the Department of Toxicology and Medication Analysis at the Vienna General Hospital (AKH Wien) and was a member of the United Nations International Narcotics Control Board. In 1997, the toxicologist conceived the Vienna drug prevention project “check it!” as its scientific coordinator. We discussed permissible limits and effective means of damage minimization with the chemist.

Here are the key points summarized:

  • Occasional cannabis users lose their driver’s licenses faster than intoxicated drivers.
  • In Germany, the permissible limit for THC in the blood is one nanogram per milliliter (ng/mL), while in Switzerland, it is three nanograms per milliliter (ng/mL). In Colorado, a limit of five nanograms per milliliter (ng/mL) of THC in the blood has been established for impairment.
  • In Austria, however, there is zero tolerance for THC in the blood while driving. As soon as traces of THC are detectable in the blood, the principle of fault applies: one becomes liable simply by consuming an illegal drug.
  • Schmid advocates for a threshold of four to five nanograms of THC per milliliter of blood as the limit for impairment in traffic. “Anything else resembles a mixture of arbitrariness and covert drug policy – and both have no place on the roads.”

How long is the statistical effect of cannabis detectable, and what conclusions can be drawn about actual impairment?

How long one is impaired after cannabis use depends on the initial amount, the type of cannabis, and the duration of acute use. On average, it should be over after six to eight hours at a moderate dose. There are now numerous scientific studies on this. The situation is different for chronic cannabis use. With regular cannabis use, THC accumulates in the body, meaning the active ingredient is not excreted as quickly and causes a longer effect. n principle, any psychoactive substance like cannabis and alcohol changes attention and perception abilities. It is beyond question that after acute use, especially in the case of chronic cannabis use, one should not be behind the wheel.

How can the extent of impairment be seriously estimated?

Trained doctors and psychologists can assess this through psychological reaction tests,as regulated in the traffic laws. In addition, the amount of THC in the blood is analyzed. The assumption is that any active substance can only exert an acute pharmacological effect as long as it is still present in the body and detectable in the circulating blood. Several studies have already examined the correlation between the acute amount of THC in the blood and impairment. Serious studies consistently come to a value of about four to six nanograms of THC in the blood, from which the psychoactive, impairing effect of cannabis is statistically detectable.

At what blood level can no impairment be detected anymore?

Below a blood level of two to three nanograms of THC in the blood, no statistically significant results can be observed. Studies conclude that a blood level of five nanograms of THC in the blood can result in impairment equivalent to about 0.05 to 0.08 percent blood alcohol. It is no coincidence that several U.S. states where cannabis has been legalized have defined five nanograms of THC in the blood as the legal limit for impairment.

Is there no significant impairment six to eight hours after cannabis consumption?

After smoking a single joint with a moderate THC content, the THC level in the blood and thus the psychoactive effect rises very quickly. However, the curve drops relatively quickly again and is within the range of one to two nanograms of THC in the blood for most test subjects after six to eight hours. Five nanograms of THC in the blood are usually exceeded after two to three hours. A problem arises, however, when THC is consumed with alcohol. Cannabis with alcohol, even in small amounts, significantly increases impairment. There also needs to be an objective legal regulation here.

How is the situation for chronic cannabis users to be assessed?

With multiple joints daily, long positive saliva samples are often found. Additionally, a low THC blood level can be detected for up to several weeks. This raises the question of whether one to two nanograms of THC in the blood of a chronic cannabis user, several days after the last joint, is still an indicator of impairment. Or is there an attempt to isolate cannabis users? This would be like documenting alcohol markers in the blood of a habitual drinker over a long period and using minimal presence as an argument for impairment. Politically, this may be popular, but whether it is fair to those affected is another question.

What do you propose?

Fundamentally, it is clear: after acute alcohol and cannabis consumption, one should not be behind the wheel. For cannabis, however, there needs to be limits, like for alcohol, that are based on medical-pharmacological evidence. A value of four to five nanograms of THC in the blood should be set as the limit for impairment in traffic. Anything else comes close to a mix of arbitrariness and covert drug policy – and neither has any place in traffic. It should be more about harm reduction. And information and education have always been the most effective means for successful harm reduction.

In Austria, lawmakers shy away from setting a limit, zero tolerance applies.

There are different political approaches to the extent to which blood values are used as an objective parameter for impairment. Some countries follow medical-pharmacological evidence – like some U.S. states – while other countries continue to follow the principle of abstinence and take one nanogram of THC in the blood or do not set a limit at all. As soon as traces of THC are detectable in the blood, the principle of fault applies: if it is not the effect, then one becomes liable simply by consuming an illegal drug. But how fair is such an approach?

Epidemiological studies are often used as an argument for the zero-tolerance stance.

Correct, so-called causation studies, where the detection of cannabis in the blood of one of the parties involved in a traffic accident is used as an argument for causality. I find that unserious.

What aspects, besides the absence of a limit, do you find problematic?

If a driver is noticeable, they must be presented to a medical officer for assessment. If the officer finds impairment due to drugs, a blood sample must be taken and sent for analysis. The analysis takes several weeks. In the meantime, the driver’s license is revoked. If the result is positive (there are no limits!), the license is revoked for six months, and there are costs for retraining. If the result is negative, the authority must bear the analysis costs. For this reason, the police demanded a preliminary test device. Since spring, a preliminary test with a saliva test system has been available in parts of Austria. However, the fact is that this system has not yet been evaluated by the police in real operations but is only used experimentally. The decision limits used are unknown, as is the extent of the drugs detected. These preliminary tests, however, influence how biased or unbiased a medical officer acts in their assessment. This is unacceptable in a constitutional state; quick action is needed here. Austria needs clear legal regulations based on objective, measurable criteria.

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