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Driving under the influence of cannabis: is it safe?

It is estimated that around 128,000 patients in Germany currently have access to legal cannabis(1). Thus, medical cannabis is becoming more widespread in this country. The number of cannabis prescriptions is growing every year(2). In addition, the Bundestag is now actively discussing the issue of recreational cannabis use and many experts are confident that the German parliament will soon fully legalize cannabis.
Therefore, discussions about how cannabis use affects a person’s daily life are more relevant than ever. One of the most important questions is how the effects of cannabis affect driving.

How does the use of cannabis affect driving ability?

Almost half of those who use cannabis (48%) are convinced that it is completely safe to use while driving. In contrast, only 14% of those who do not use cannabis agree that driving under the influence is safe. This data was provided by PSB Research and Buzzfeed News(3). Opinions are strongly divided, but what is the truth?
In 2010, the American Journal of Addiction published a study that concluded that cannabis does not have a significant negative impact on driving(4). Yes, in purely theoretical terms, cannabis’ psychoactive cannabinoid, THC, can impair attention span and time and speed perception. In reality, however, one sees quite different results.
In a 2017 experiment, participants were asked to drink alcohol or consume marijuana, and then they were tested in a car simulator. The result: the drivers who consumed cannabis showed a more careful driving style: they drove more slowly and kept more distance between cars.
So medical cannabis only theoretically makes you a more vulnerable and inattentive driver (since medical marijuana does not contain high levels of THC). But in fact, a driver under the influence of cannabis is not a danger to himself and other road users.
Taking the U.S. experience and analyzing the number of accidents in U.S. states where cannabis is legal or prohibited, no causality can be seen between legalization and an increase in fatal collisions. Most modern research says that alcohol consumption endangers driving safety more than cannabis use.

German laws and regulations

In 1998, Germany passed a law on driving under the influence of prohibited substances. At that time, everything from alcohol to cocaine, including cannabis, was classified as an illegal substance. This means that if you are stopped by the police for driving under the influence of drugs, one of the following two events may occur:

  1. The police request a blood sample if the driver shows clear signs of intoxication. In case of a positive result, the case is forwarded to the court due to the initiation of criminal proceedings..
  2. The police will request a urinalysis if the symptoms of intoxication are not pronounced. If the result is negative, the driver is discharged. But a positive result entails the obligation to take a blood test. If the test is positive, the driver will be brought to administrative responsibility (fine € 500 + revocation of the driver’s license for 3 months).

In 2017, an important event took place: Cannabis was legalized in Germany for therapeutic purposes, i.e. products containing cannabinoids were equated to pharmaceuticals and could be sold in pharmacies on prescription with immediate effect. Since taking medical cannabis on prescription cannot result in a driving ban, an appropriate controversy arises: What does the law say about drivers when THC is found in their blood?

Negative effects of the current legal situation

The fact is that cannabis affects the human body differently than alcohol. THC can be present in the blood for up to 30 days after consuming cannabis. Does this mean that citizens are obliged to give up driving? Not at all. Patients who regularly use medical cannabis for therapeutic purposes will always exceed the test limit of 1 nanogram per milliliter of tetrahydrocannabinol.
Incidentally, in 2015 a group of experts proposed raising the permissible limit from one nanogram per millimeter to three nanograms. But so far the restrictions remain the same and continue to cause contradictions between the laws. In this case, the tests should also be carried out differently.
It turns out that patients who have prescriptions for medical marijuana are at risk: They can be fined if banned substances are found in their body, lose the right to drive a car, as well as be denied insurance payments in case of accidents. Moreover, if your driver’s license is revoked for 3 months, you will have to pass the MPU test to get it back.

MPU information: Problems and challenges

The MPU (Medical-Psychological Examination) is a test that checks your suitability to drive a motor vehicle in Germany. The main purpose of the procedure is to assess whether you can behave safely in road traffic for yourself and others.
You will be asked certain questions about your state of health and complete tests on concentration, reaction speed and knowledge of traffic rules at the driver’s license office. The cost of the MPU varies between €530 and €1000, depending on the circumstances of the assessment. If you are taking the MPU due to drug problems, you will also have to provide a urine sample. Authorities now position this procedure as an effective method of reducing recidivism among drivers who have previously violated traffic laws while under the influence of alcohol or drugs.

THC half-life in the body

The effect of cannabis occurs within a few minutes or hours, depending on the form of consumption. However, THC can still be detected in the body for up to a few days or even weeks. To properly understand how long it takes your body to metabolize THC, you need to learn about the principles of human metabolism.
The elimination half-life of a substance can be understood as the amount of time it takes for the concentration of a substance to drop to half of the initial dose. However, the substance can be detected much longer after the elimination half-life. For THC, the half-life depends significantly on the dosage and frequency of use of cannabis products:

  • For those who rarely use cannabis; that’s an average of a day and a half;
  • For regular users it can be 5-13 days (and according to some studies up to 30 days).

This means that the drug test is likely to show a positive result for up to 12 days in patients who use infrequently and up to 30 days in patients who use regularly. The form of use is also important. When smoking, the maximum THC concentration is reached after 3-8 minutes, when ingesting – after 1 hour.
In summary, the duration of cannabis degradation in the blood varies widely and laws and regulations do not provide clear guidance. All this leads to misunderstandings when it comes to testing. Therefore, if you know that you are going to be tested for drugs soon, experts advise you to refrain from using cannabis for 14-30 days. However, the experts cannot answer what patients who take cannabis products for therapeutic purposes should do.

Information for doctors and pharmacies

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General information on medicinal cannabis

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So kaufen Sie medizinisches Cannabis in Deutschland?
Seit dem Inkrafttreten des „Cannabis als Medizin” Gesetzes am 10. März 2017 ist die Verschreibung von Cannabis in Deutschland zu therapeutischen Zwecken legal. Unter ärztlicher Anleitung können Patienten ein Rezept für medizinisches Cannabis erhalten und damit medizinisches Cannabis in verschiedenen Formen erhalten und anwenden.