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Germany’s New Per Se Cannabis Driving Law Is The Wrong Approach

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One of the most serious topics in cannabis policy modernization discussions is how to mitigate the dangers of people driving under the influence of cannabis. If there is one thing that cannabis opponents and responsible cannabis advocates agree on, it is that no one should operate a motor vehicle on a public roadway when they are intoxicated.

Yet, whereas opponents and supporters can agree on that basic premise, the two sides diverge when it comes to how cannabis DUI enforcement should be handled. In every jurisdiction that has modernized its cannabis policies to permit adult use, cannabis opponents have pushed for enforcement practices that are not backed by science.

Germany is the latest jurisdiction to experience this scenario. Lawmakers in Germany adopted a per se cannabis DUI law this week, and drivers in Germany will now be subjected to a 3.5 ng/mL THC limit.

“The amendment to the Road Traffic Act is intended to introduce a THC (tetrahydrocannabinol) limit in road traffic and a ban on alcohol for cannabis users.” The Bundestag stated on its website.

“According to the new regulation, the limit will be 3.5 nanograms per milliliter in the future. If the limit is exceeded for the first time, there is a risk of a fine of 500 euros and a one-month driving ban.” the Bundestag also stated about the recently adopted measure.

Per se THC DUI limits are a knee-jerk public policy reaction by cannabis opponents. Opponents spend a considerable amount of time falsely hyping up imaginary ‘terror on the roadways’ doomsday scenarios leading up to legalization, including in Germany, and per se THC limits are their ‘solution’ to the imaginary problem that they themselves established using false pretenses.

Unfortunately, per se THC limits often resonate with many members of society due to per se alcohol limits being common, including in Europe. Per se blood alcohol limits in Europe range from zero tolerance in places like Hungary and the Czech Republic to .08 in the United Kingdom. The United States also has a national .08 limit, although state-level limits can vary in some circumstances.

While per se limits for blood alcohol levels are based on sound science, the same is not true for cannabis due to a multitude of factors, not the least of which is how the human body metabolizes THC. The human body does not metabolize alcohol and THC in the same manner.

According to a 2021 analysis conducted in Australia, cannabis impairment can last “between three and 10 hours” when consumption involves “moderate to high doses of the intoxicating component of cannabis, tetrahydrocannabinol (THC).” The analysis involved data from over 80 different studies spanning a period of over 20 years.

THC impairment may only last 3 to 10 hours, but metabolized THC can stay in a person’s system for as long as 100 days, well beyond the window of impairment. Depending on how much THC the user consumed and their metabolism rate, the consumer could easily have more than 3.5 ng/mL of THC in their system for weeks or months into the future.  Those consumers will not be impaired at all, and yet still run afoul of Germany’s new cannabis law.

The 3.5 ng/mL threshold in Germany is completely arbitrary, as there is no sound science demonstrating that such a limit automatically equates to impairment. In fact, a study conducted in Canada in 2019 found “no evidence of increased crash risk in drivers with Δ-9-tetrahydrocannabinol < 5 ng/ml and a statistically non-significant increased risk of crash responsibility (odds ratio = 1.74) in drivers with Δ-9-tetrahydrocannabinol ≥ 5 ng/ml.”

Another study conducted in Canada (2024) involving simulated driving data found that the presence of THC in blood is not predictive of detriments in psychomotor performance. The findings are in line with a separate government-funded study in the U.S. that also found that “there was no correlation between THC (and related metabolites/cannabinoids) in blood, OF [oral fluid], or breath and driving performance.”

“The complete lack of a relationship between the concentration of the centrally active component of cannabis in blood, OF, and breath is strong evidence against the use of per se laws for cannabis.” the researchers stated about the government-funded study. Researchers at Yale University also arrived at the same conclusions in a study in 2021.

Germany’s 3.5 ng/mL threshold will likely put a massive burden on the nation’s court system, with countless drivers being falsely accused of operating a motor vehicle while intoxicated. Offenders will have an affirmative defense and will be able to point out that just because they had THC in their system did not automatically mean that they were impaired at the time in question.

Cases involving those set of circumstances will presumably be disaffirmed, but only after a considerable amount of time and money was wasted for both the accused and the courts.

The cannabis plant is complex and how it interacts with human biology is dynamic. There is no one-size-fits-all approach to cannabis impairment as it pertains to operating motor vehicles on public roadways. Germany would be far wiser to implement a comprehensive approach to determining impairment, including the incorporation of various field sobriety tests.

They are less intrusive and are more effective at spotting actual impairment. Field sobriety tests, combined with public awareness campaigns educating consumers about the dangers of driving while impaired and the benefits of pursuing public transit options, are a much better strategy than per se limits.

Until Germany implements more sensible cannabis DUI laws, consumers in Germany are encouraged to take public transit as much as possible.