Cannabis use while driving: Do or don't?

The legalization of cannabis in April 2024 has opened up many questions and problems that society has never had before. Among other things, what regulations apply to Cannabis and the road traffic must, should, or may apply. Until now, the answer was quite clear: No. But what's the situation now? Have the strict regulations changed? Are you now allowed to smoke weed 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 driving while drunk is an absolute no-go. You have to be fit to drive, and if you're stoned as a beach howitzer behind the wheel, that's hardly the case. But as with alcohol, the substance has effects that extend beyond the consumption window and, depending on the amount consumed, can leave you incapacitated for quite some time afterwards. We're talking, of course, about blood alcohol, or the THC content in your blood. Even if you feel sober, the values ​​must be correct in order to meet the applicable requirements for cannabis in road traffic. For alcohol, this limit varies depending on the circumstances. For example, novice or professional drivers don't have to be able to prove they have any blood alcohol content at all, i.e. 0,0 per mille. For most other people, however, the following applies: Up to 0,3 per mille, you are still not considered unfit to drive and you don't always have to face consequences. Usually, even up to 0,5 per mille, a blind eye is turned, but if your blood alcohol level is higher, you can expect a fine in any case. Please note: This applies to mere checks where you show no abnormalities. If you exhibit signs of impairment or are involved in an accident, this can be punished as an administrative offense or even a criminal offense even with a lower blood alcohol level! Added to this are the occasional points on your license and a driving ban. For most drivers, this means: Having a beer with friends and then driving home is fine – as long as "a beer" is also a Beer means.

And even with cannabis in road traffic, there were legalization There is already a regulation: 1 ng/ml blood serum. This limit is reached quite quickly and is essentially equivalent to a zero limit. Especially with today's THC content of cannabis, which is sometimes well over 20%, half a joint is enough to break the threshold – when consumed with Vaporizer It's even faster. Shortly after legalization, a new limit was set for cannabis in traffic.

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 report of the expert working group also states that long-term users showed an average value of 4,8 ng/ml blood serum – but without simultaneous impairment of 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 Road Traffic Act (StVG) regulates the handling of Cannabis in traffic Pretty strict. If the current limit is exceeded, the driver is considered unfit to drive, even if there are no driving errors or obvious impairments (aha?). Those caught driving with cannabis face rather undesirable 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 the suspension of a driver's license and the ordering of an MPU (medical-psychological examination). This, of course, is something you want 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.

… tiredness or drowsiness: Cannabis can have a sedative effect, especially at high doses.

… risk-taking: Some studies show that cannabis can affect judgment and lead to riskier behavior.

… limitations in decision-making ability: Situations are assessed less effectively and decisions take longer.

… panic or anxiety: This can negatively influence the behavior in traffic, especially for 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 on prescription are subject to special regulations, but driving ability remains a central issue here as well – it would be counterproductive if all prescription users were released into traffic unfit to drive. In principle, patients with medical cannabis in road traffic be on the road, provided they are not impaired. The responsibility lies with the driver, who must assess for themselves whether they feel fit to drive. However, the legal THC limit of 3,5 ng/ml in blood serum applies equally to medicinal and recreational users. At first glance, that doesn't sound all that different.

The crucial difference: Patients with medically prescribed cannabis can rely on their treatment in the event of a check. However, this is not a free pass. Anyone who is stopped while driving under the influence of cannabis and is 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 adjustment phase or when changing dosage. However, regular consultations with the treating physician help to identify possible Nebenwirkungen to monitor. If your doctor agrees, you could also occasionally have your blood levels tested, as this will ensure you always know exactly what level you're at with your consumption. In most cases, cannabis prescriptions aim to keep the prescribed amount as low as possible to minimize the psychoactive effects. As a pain patient who really has to consume a lot, things are different, of course, 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.