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Regular Cannabis Use Likely to Increase the Risk of Accidents Causing Personal Injury.

Regular use of drugs such as cannabis is one of the major risks for road users. The problem is that the cannabis plant and its products contain the active ingredient tetrahydrocannabinol (THC), which has a psychoactive effect on the entire central nervous system and influences all human senses. "This should by no means be taken lightly," says Dr. Thomas Wagner, traffic psychologist and head of the department of the officially recognized driver fitness assessment centres at DEKRA in Germany. "Users of cannabis products who drive a motor vehicle after ingesting the psychoactive substance endanger road safety on the one hand and also give rise to doubts about their fitness to drive on the other." This applies even more so in cases of frequent or regular consumption of the supposed "lifestyle drug."

Cannabis use by road users is one of the topics highlighted in the 2022 DEKRA road safety report "Mobility of Young People."

  • Initial contact with so-called "lifestyle drugs" often comes at a young age

  • Impairment of motivation and performance

  • Good reasons for setting THC threshold value in road users

Statistics from the German Federal Ministry of Health's Drug and Addiction Report are good causes to sit up and take notice. According to the report, 10 % of all young people in Germany between the ages of 12 and 17, 42.5 % of young adults between the ages of 18 and 25, and around 28 % of adults up to the age of 64 have used cannabis in their lifetime. 1.6 % of young people and 6.9 % of young adults do so regularly. Various studies have shown that the high-risk period for first use is between 16 and 18.

Alongside danger to health and reduced educational opportunities, cannabis use is also associated with an increased risk of road traffic accidents. "The extent of cannabis use is closely related to driving under the influence of substances and risky driving behaviour," indicates Dr. Thomas Wagner. For example, people are susceptible to this if they are looking for extreme experiences, have low self-control, or have a risk-friendly personality structure.

"The consequences of frequent, regular, and in particular of, chronic cannabis use is multifaceted and may include components of both motivation and performance," explains the DEKRA expert, referring, among other things, to his own research findings and studies that he compiled and evaluated together with Professor Dieter Müller of the Institute for Traffic Law and Traffic Behaviour in Bad Dürrenberg, Germany, for a recent article on the subject of cannabis use by road users in "Zeitschrift für Verkehrssicherheit" (Journal for Road Safety).

"All the cognitive processes that are important for safe driving can be impaired," Dr. Wagner says. That is, concentration, attention, reaction time, short-term and working memory, psychomotor skills, and perception of time and space. Concerning motivation, what is known as "amotivation syndrome" in long-term users has long been known. This presents apathy and loss of drive, inspiration, and interest, negatively affecting driving tasks' safe performance.

Impacts on driving safety

The unsafe driving observed after cannabis use mainly involves lane keeping, driving speed regulation, and dealing with rules about right of way at traffic lights or intersections. In addition, particularly among young drivers, conspicuous features such as slower driving, crossing the centre line more frequently with increased abrupt steering wheel movements, and prolonged reaction times can be observed in connection with the use of cannabis.

There are currently no official statistics on accident numbers, criminal offenses, or administrative offenses concerning cannabis for Germany. However, according to the Federal Statistical Office, the number of accidents resulting in personal injury due to the influence of intoxicating substances (other than alcohol) increased more than sevenfold between 1975 and 2020: from 323 to 2,366. Men accounted for 2,110 of these accidents, just under 90 %. Furthermore, epidemiological studies from other countries consistently show an increased risk of accidents causing personal injury by a factor of 1.26 to 2.66 and an increased risk of fatal accidents by a factor of 1.31 to 2.10 for drivers after ingesting cannabis products.

"Therefore, there are perfectly good reasons for setting a threshold value for THC that enables the reliable identification of risk carriers among road users," says Dr. Thomas Wagner. In Germany, this value is 1.0 nanogram per milliliter of blood serum, which currently constitutes the threshold for an administrative offense. It also marks the point at which a person's fitness to drive a motor vehicle is called into question and requires evaluation, as it is not possible to adequately exclude the possibility of impairment of safe driving. One-time, sporadic or infrequent cannabis users, on the other hand, do not pose an increased risk to road safety.

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