—— The decriminalization of cannabis in Germany means fewer changes for drivers than might be expected. TÜV SÜD traffic psychologist Thomas Wicke talks about the significance of threshold values, the need for more research and why, if in doubt, it is better not to get behind the wheel.

Mr. Wicke, could you give us an overview of the current situation concerning cannabis and driving in Germany?
———— Cannabis is the most commonly consumed illegal drug in the country. Researchers suspect that around two-thirds of all drug-impaired driving occurs under the influence of cannabis. The number of medical-psychological assessments rose from 15,000 to 27,000 between the years 2010 and 2022, with the largest increase in the cannabis sector, while numbers for alcohol are declining. Cannabis has become a lifestyle drug and is thus becoming increasingly common in road traffic.
What developments do you expect due to the decriminalization of cannabis?
———— I expect the numbers to increase even further, simply because of greater availability and ease of purchasing. However, one of the major problems here is determining someone’s fitness to drive. In the case of alcohol consumption, a blood alcohol level of 0.5 per milliliter is considered a misdemeanor, while above 1.1 means a person is legally unfit to drive. We don’t have comparable values for cannabis.
That brings us to the topic of “threshold values” — how is this currently being dealt with?
———— What is measured for cannabis use is what is known as the tetrahydrocannabinol, or THC value. Currently, a blood concentration of 1.0 nanograms per milliliter constitutes a misdemeanor. This value is controversial, as it is set very low. A value of 3 nanograms is also being considered. However, I would argue that neither value is sufficiently scientifically substantiated. There’s a lack of systematic research that can unequivocally determine the point beyond which the risk of an accident actually increases. Due to the metabolic processes involved with cannabis, which are very difficult to understand, it is hard to judge how impaired someone is by the THC value alone. Until there is more clarity here, I believe that road safety should be prioritized and a lower threshold value should be maintained.
Cannabis can be detected in the blood even after the period of impairment may have passed. What difficulties does this pose?
———— It cannot be said with certainty that a person with 10 nanograms of THC in their blood drives more dangerously than someone with 2 nanograms. According to one study, the differences are sometimes less dramatic than one might think. That’s what makes defining a threshold value so difficult. Much more research is needed on this topic, but so far we’ve been dealing with an illegal substance, which has made it impossible to carry out any direct studies on it.
With alcohol, most people know when the applicable threshold has been exceeded — there are certain rules of thumb to use as guides. Is there something similar for cannabis?
———— Unfortunately, that is not possible. To be relatively certain that I don’t have any more THC in my blood, I have to wait at least three days, if not longer. With cannabis, consumption behavior has a decisive influence on the length of the period of detectability. On top of this, it’s also much more difficult for me to estimate how much THC I’ve ingested. It could become necessary, for example, to limit cultivation of cannabis only to particular varieties in order to better estimate the concentration of THC and thus the duration of the effects.

"I am afraid that some people will not realise that nothing will fundamentally change in terms of the legality of road traffic".

So according to the current threshold values, you couldn’t consume cannabis over the weekend and then drive your car to work on Monday?
———— We can only recommend using cannabis extremely rarely if you really want to. Because if you do use it regularly, you will never get below the threshold value of 1.0 nanogram. At the moment, I’m still not seeing more comprehensive communication about this for the general public. I fear that some people are not really aware that nothing will fundamentally change in terms of legality and driving.
What can we learn from other countries where legalization or decriminalization has already occurred?
———— Not much, unfortunately. On this topic we often look to the Netherlands, but I’m not familiar with any findings on road traffic and driving from there. There is also very little research from other countries on the subject of cannabis and driving. One reason for this might be that the number of accidents caused by alcohol continues to be significantly higher and thus attracts more scientific research. In Germany, we should take this opportunity to obtain meaningful data. We should explicitly record the incidence of cannabis consumption in the accident statistics. A more sensible threshold value requires better research and we need sufficient monitoring resources to determine how the figures develop over time.
In which areas is TÜV SÜD involved in the issue of road safety and the effects of decriminalization?
———— The assessment unit of TUV SÜD can contribute its experience of driver fitness, for example by reporting any increase in more serious cases. I work in the field of counseling, and we don’t get involved until mistakes have already been made, at which point we support drivers in changing their consumption habits and ultimately becoming mobile again.
How many people who lose their driver’s license due to cannabis use manage to get it back?
———— The success rate is quite good. This is because they have to continually prove that they’re remaining abstinent, in other words that they are no longer using. This is often sustainable over the long term, with a relapse rate of just 4.5 percent.

Thomas Wicke is a traffic psychologist and has been the technical director of TÜV SÜD Pluspunkt since 2008. Through training sessions and courses, he helps people whose driver’s license has been suspended—for example, due to alcohol or drug use—to make lasting positive changes in their behavior. This is the basic prerequisite in Germany for regaining a driver’s license and is known as the medical-psychological assessment.