Cannabis use while driving: Do or don't?

With the legalization of cannabis in April 2024, many questions and issues arose that society had never faced before. Among them was the question of what regulations should, must, or may apply to cannabis and road traffic . Until now, the answer was a clear no. But what about now? Have the strict regulations changed? Is it now legal to smoke cannabis and drive? Let's take a look together!

THC limit(s) for cannabis in road traffic in Germany

Smoking weed and driving is obviously out of the question, just as drunk driving isn't a complete no-go. You must be fit to drive, and if you're as high as a kite behind the wheel, that's hardly the case. But, as with alcohol, there are effects of the substance that extend beyond the window of consumption and, depending on the amount consumed, can leave you incapacitated for quite some time afterward. We're talking, of course, about blood alcohol content, or more specifically, the THC level in your blood. Even if you feel sober, these levels must be within the legal limits to comply with the regulations regarding cannabis use while driving. With alcohol, this limit varies depending on the circumstances. For example, novice drivers or professional drivers don't have to prove any blood alcohol content at all, i.e., 0,0 per mille. For most other people, however, up to 0,3 per mille, you're still considered fit to drive and don't necessarily have to face consequences. In most cases, even a blood alcohol level of 0,5 per mille is overlooked, but if your blood alcohol is higher, you can expect a fine. Important: This applies to routine checks where you don't exhibit any signs of impairment. If you show signs of impairment or are involved in an accident, this can be prosecuted as a traffic violation or even a criminal offense, even with a lower blood alcohol level! In addition, you'll likely receive points on your license and face a driving ban. For most drivers, this means: Having a beer with friends and then driving home is fine – as long as "a beer" actually means a beer.

Even before legalization , there was already a regulation regarding cannabis use in road traffic: namely, 1 ng/ml of blood serum. This limit is reached quite quickly and is essentially a zero limit. Especially with today's THC content in cannabis , which is sometimes well over 20%, half a joint is enough to exceed the threshold – and it happens even faster when using a vaporizer . Shortly after legalization, a new limit for cannabis use in road traffic was introduced.

The new THC limit for driving

According to official information, in order to establish a new regulation regarding cannabis in road traffic, a commission of experts was set up to assess the minimum THC limit for driving, the amount of cannabis required to achieve this, and so on. The decision was then made: The new THC limit for cannabis in road traffic has been 5 ng/ml blood serum since July 2024, 3,5. However, it is not clear why. According to studies, there is no increased risk of accidents up to 7 ng/ml (see table). Perhaps they wanted to set a precedent and say: please don't smoke weed and drive. Perhaps one of the commission members had a problem with the number 7. Perhaps—and we're just throwing this out there—perhaps they simply lacked their own experience and contact with the topic, and therefore, unfortunately, had incomplete understandings of reality. The following table can be found in the recommendation of the interdisciplinary expert group that developed the proposal regarding cannabis in road traffic:

For comparison: A THC level of 7 ng/ml would correspond to approximately the same impairment as 0,1–0,5% blood alcohol. Why a significantly lower limit was chosen? We don't know either. 

Incidentally, the expert working group's report also states that regular users showed an average blood serum level of 4,8 ng/ml – but without any simultaneous impairment of their driving ability. Here, too, the current regulations regarding cannabis in road traffic don't seem to make much sense.

Cannabis and the Road Traffic Act (StVG)

The German Road Traffic Act (StVG) regulates the use of cannabis in road traffic quite strictly. If the currently applicable legal limit is exceeded, the driver is considered unfit to drive, even if there are no driving errors or obvious impairments (really?). Those caught driving under the influence of cannabis face rather unpleasant consequences, such as a fine of at least €500, two points on their license, and a one-month driving ban – even for a first offense. Repeated offenses or conspicuous driving behavior can even lead to license revocation and a mandatory medical-psychological assessment (MPU). Naturally, this is something one wants to avoid.

However, we do have one small security measure for you: The police are generally not allowed to randomly pull out and test road users, as strict regulations apply here as well – and they protect you. For a test to be conducted, at least one of the following conditions must be met:

• Unusual driving behavior (e.g. difficulty staying in lane).

• External signs of consumption such as the smell of cannabis or dilated pupils.

• Cannabis lying around openly.

• An accident.

But what exactly happens to your ability to drive on the road if you have consumed cannabis?

Effects of cannabis consumption on driving ability

As you can see from the table above, cannabis affects the body in various ways. Among them are reduced reaction time, poor concentration, and reduced fine motor skills. In addition,

… distorted perception : speed, distances and dangers are misjudged.

…reduced attention span : Multitasking ability is limited, which is problematic in complex traffic situations.

… Fatigue or drowsiness : Especially at high doses, cannabis can have a sedative effect.

… Risk tolerance : Some studies show that cannabis can affect judgment and lead to riskier behavior.

… Limitations in decision-making ability : Situations are assessed less accurately, decisions take longer.

… Panic or anxiety : This can negatively affect road traffic behavior, especially in inexperienced consumers.

… reduced memory performance : Short-term information (e.g., traffic signs) is processed less effectively or forgotten.

Especially for occasional users, even low levels of THC can endanger road safety. Of course, this all depends on how much was consumed, how your body reacts, and so on. To ensure you're fully fit to drive, the ADAC recommends waiting at least 24 hours after consumption before getting behind the wheel again. You should approach anything below this with a bit of healthy self-assessment, be aware of the potential risks, and, above all, seriously consider whether you consider yourself a danger to yourself and other road users. If in doubt, it's better to get an outside assessment!

And what about medical cannabis in traffic if it is consumed on prescription?

Patients who receive cannabis by prescription are subject to special regulations, but fitness to drive remains a central issue – it would be counterproductive if all prescription users were released onto the road unfit to drive. Generally, patients with medical cannabis are allowed to drive , provided they are not impaired. The responsibility lies with the driver, who must assess whether they feel fit to drive. The legal THC limit of 3,5 ng/ml in blood serum applies equally to medical and recreational users. At first glance, that doesn't sound so different.

The crucial difference: Patients with medically prescribed cannabis can cite their treatment if stopped by the police. However, this is not a free pass. Anyone stopped while driving under the influence of cannabis and clearly unfit to drive – for example, due to fatigue, dizziness, or reduced reaction time – risks legal consequences despite having a prescription. To drive safely, patients should first check how their body reacts to the prescribed dose. Caution is particularly advised during the initial adjustment period or when changing the dose. Regular consultations with the prescribing doctor help monitor potential side effects . If your doctor agrees, you could also have your blood levels tested occasionally, as this way you always know exactly where you stand with your consumption. In most cases, cannabis prescriptions aim to keep the prescribed amount so low that the psychoactive effects remain minimal. As a pain patient who really needs to consume a lot, the situation is naturally different, and you can expect to be permanently above the permitted limit of 3,5 ng/ml.

And what about long-term cannabis use while driving?

Surprisingly, long-term cannabis users can be at increased risk of traffic accidents despite having THC levels below the legal limit. Studies show that regular use also has long-term effects on cognitive and motor skills, which are crucial, if not fundamental, for safe road use. Even with blood THC levels below 3,5 ng/ml, chronic users can still be impaired. Conversely, however, it's also possible that with "medium-term use," blood levels are too high, but driving ability is not impaired.

However, studies suggest that the ability to react quickly, hand-eye coordination, and the ability to assess dangerous situations can be significantly impaired in long-term users. These cognitive changes therefore also have a negative impact on road safety. An increased risk of accidents could therefore exist for long-term users even if the THC level does not immediately exceed the legal limit. This is because regular use can lead to the development of tolerance, in which the substance's effects are less intense, but the body's own adaptations still impair driving ability. Furthermore, research shows that long-term users are more likely to engage in riskier driving behavior, which further increases the risk of accidents. Combined with a potential reduction in judgment and attention, the risk of accidents remains elevated even with low THC levels. So, it's a fun situation – you won't get a fine because your blood test results were correct, but it's far from ideal.

Cannabis in traffic: What do I do with the information now?

Cannabis in traffic isn't all that easy. There's a lot of information, some of the regulations are somewhat confusing, and you can't just do a blood test at home to see for yourself where you are. So what should you do? We'd stick to the following:

And if you were hoping you'd be able to drive without consequences after cannabis legalization, we're very sorry. And to return to our initial question, "Cannabis in Traffic: Do or Don't": Don't.