Driving Licence and Cannabis: What You Need to Know

The partial legalization of cannabis through the KCanG changed little in one area: road traffic. Driving while under the influence of cannabis still risks severe consequences – from fines to licence revocation to the dreaded MPU (Medical-Psychological Assessment). At the same time, the rules have changed in important details: a new THC limit has been introduced, the mixed-use prohibition with alcohol has been tightened and detection methods have been refined. This article comprehensively explains what cannabis users need to know about road traffic to protect their driving licence.

## The THC Limit: 3.5 Nanograms Per Millilitre

With the amendment to the Road Traffic Act (StVG), which came into force simultaneously with the KCanG, a binding THC limit for road traffic was established for the first time: 3.5 nanograms of THC per millilitre of blood serum. This value was chosen on the recommendation of an interdisciplinary expert commission convened by the Federal Ministry of Transport.

### Why 3.5 ng/ml?

The limit is based on scientific evidence regarding driving fitness. Studies show that at a THC concentration of 3.5 ng/ml in blood serum, relevant impairment of driving ability begins, roughly equivalent to the impairment at 0.2 per mille blood alcohol. The expert commission deliberately chose a conservative value below the threshold at which significant performance deficits are demonstrable in driving simulator studies (typically from 5–7 ng/ml).

### What Does the Limit Mean in Practice?

Unlike alcohol, there is no linear relationship between cannabis consumption quantity and blood concentration. THC pharmacokinetics are complex: after smoking cannabis, the THC concentration in the blood rises to peak levels within minutes but then falls rapidly. In occasional users, the level typically drops below 3.5 ng/ml within 3 to 6 hours. In regular users, however, THC can remain detectable due to storage in fatty tissue for days or even weeks – even above the limit, although no acute intoxication is present.

This discrepancy between detectability and actual impairment is the central problem of the THC limit. While a regular user may drive to work in the morning with a THC level above 3.5 ng/ml without feeling subjectively impaired, they are legally considered unfit to drive. Conversely, an occasional user may fall below the limit just a few hours after consumption, even though residual effects may still be present.

### Comparison with Other Countries

The German limit of 3.5 ng/ml falls in the international middle range. The Netherlands applies a limit of 3 ng/ml, Norway 1.3 ng/ml (effectively zero tolerance). Canada has a tiered approach: 2 to 5 ng/ml counts as a lesser offence, above 5 ng/ml as a serious criminal offence. Colorado (USA) has a limit of 5 ng/ml as a permissible inference threshold, at which impairment is presumed but can be rebutted.

## Controls: How Is THC Detected in Road Traffic?

### Suspicion-Based Controls

In Germany, drug controls in road traffic are suspicion-based: police officers must have initial grounds for suspicion before they can order a drug test. Typical indicators that establish suspicion include reddened eyes, slowed reactions, dilated pupils, cannabis odour in the vehicle, conspicuous driving behaviour or nervous behaviour during the check.

### Preliminary Tests: Saliva and Urine

At the roadside, a rapid test is first conducted – typically a saliva test (Dräger DrugTest or Securetec DrugWipe). These tests are preliminary and have no legal evidentiary value. They can produce false-positive or false-negative results. However, a positive preliminary test authorizes the police to order a blood draw.

Urine tests are also used but are less common. They do not detect THC itself but the metabolite THC-COOH, which can remain detectable in urine for weeks. A positive urine test therefore says nothing about current impairment – it merely indicates past consumption.

### The Blood Draw: The Only Legally Binding Test

Only a blood draw performed by a physician provides legally admissible evidence of THC concentration. The police can have a blood draw ordered by a judge under § 81a StPO or order it themselves when there is imminent danger. In practice, officers on the scene often decide themselves, as a judge may not be reachable promptly. The blood sample is analysed in an accredited laboratory using gas chromatography-mass spectrometry (GC-MS) – the gold standard of forensic toxicology.

Important: The blood draw is a physical intervention and fundamentally only permissible with a judicial order or in cases of imminent danger. You have the right to request a judicial order. In practice, however, this often only leads to delays rather than prevention of the blood draw.

### May I Refuse the Preliminary Test?

Yes. Saliva and urine tests at the roadside are voluntary. You are not obliged to consent to a preliminary test. However, the police can order a blood draw based on reasonable suspicion even without a positive preliminary test. Refusal of the preliminary test may also be viewed as suspicion-reinforcing behaviour.

## Mixed-Use Prohibition: Cannabis and Alcohol

The KCanG introduced an absolute mixed-use prohibition for cannabis and alcohol in road traffic. Anyone who drives a motor vehicle while under the simultaneous influence of cannabis and alcohol commits an administrative offence – regardless of whether the individual limits are each met. This means: even with a THC level of 1 ng/ml and an alcohol level of 0.1 per mille – both well below their respective limits – a violation is committed.

This strict prohibition is medically justified. Cannabis and alcohol mutually amplify their effects on driving fitness (synergistic effect). Studies show that the combination of both substances impairs reaction time, attention and lane-keeping more severely than the sum of their individual effects would suggest.

The fine for a mixed-use violation is 500 euros and a one-month driving ban – for the first offence. Sanctions increase significantly for repeat offences.

## Detection Times: How Long Is THC Detectable in Blood?

The detection time for THC in blood varies considerably between individuals and depends on numerous factors.

### Occasional User (less than once per week)

In occasional users, the THC level after smoking a single dose typically drops below the 3.5 ng/ml limit within 3 to 6 hours. After 24 hours, THC is generally no longer detectable in blood at relevant concentrations.

### Regular User (several times per week)

With regular use, THC accumulates in fatty tissue and is slowly re-released. The THC level can remain above 3.5 ng/ml for days after the last consumption. Studies show that daily users can have THC values above the limit up to 7 days after their last use. In individual cases, THC values above 3.5 ng/ml have been measured in very heavy long-term users even after 30 days of abstinence.

### Influencing Factors

Numerous factors influence individual detection time: body fat percentage (THC is fat-soluble – higher body fat means longer storage), metabolic rate, frequency and quantity of consumption, form of consumption (smoking vs. oral intake – with edibles absorption is slower but so is elimination), physical activity (exercise can release THC from fatty tissue and temporarily raise blood levels) and hydration.

### THC-COOH: The Metabolite in Urine

The THC metabolite THC-COOH (11-nor-9-carboxy-THC) is detectable for significantly longer than THC itself. In urine, THC-COOH can be detected for 3 to 5 days in occasional users, 2 to 4 weeks in regular users and up to 12 weeks in chronic users. THC-COOH is not directly relevant for road traffic (only the THC value in blood counts), but a positive urine test can prompt the driving licence authority to question fitness to drive.

## MPU: The Medical-Psychological Assessment

The MPU – colloquially called the idiot test – is for many affected individuals the most severe consequence of a cannabis violation in road traffic. It can be ordered by the driving licence authority when doubts about fitness to drive exist.

### When Is an MPU Ordered?

Typical triggers for a cannabis MPU include: driving under THC influence above the limit (particularly for repeat offences), conspicuous behaviour in road traffic associated with cannabis, possession of larger quantities of cannabis (even without a traffic offence, if the driving licence authority learns of it) and medical or police reports suggesting regular cannabis use.

The driving licence authority has discretionary latitude. Not every cannabis violation automatically leads to an MPU. For a first-time offence with a low THC level, the authority may also order milder measures such as a medical report or an abstinence programme.

### Course of the MPU

The cannabis MPU consists of three parts: a medical examination (physical examination, blood values, liver values), a psychological exploration (extensive conversation with a traffic psychologist about consumption behaviour, capacity for insight and behavioural change) and performance tests (reaction ability, attention, resilience).

The decisive part is the psychological conversation. The assessor evaluates whether the person has reflected on their consumption behaviour, whether a stable behavioural change has occurred and whether there is a risk of repetition. Standardised answers or obviously rehearsed statements are evaluated negatively.

### Abstinence Verification

As a rule, abstinence verification is required for the MPU. Common methods include: urine screenings over 6 or 12 months (4 to 6 random tests) or hair analysis (one centimetre of hair length corresponds to approximately one month – for a 6-month verification, 6 cm of hair is needed). Since the KCanG, the question of abstinence has become more nuanced: as cannabis is legal, the driving licence authority can no longer blanketly require total abstinence. Instead, it must be demonstrated that consumption and participation in road traffic are reliably separated. The precise requirements, however, have not yet been conclusively settled by case law.

### Costs and Duration

The MPU itself costs between 350 and 750 euros. Additionally, there are costs for abstinence programmes (200–500 euros), preparatory counselling or courses (300–1,500 euros) and possibly a lawyer. The entire procedure – from the order through the abstinence phase to passing the MPU – typically takes 6 to 18 months.

### Failure Rates

The failure rate for cannabis MPUs is approximately 35 to 45 percent on the first attempt. The most common reasons for failure are: lack of insight into one's own consumption behaviour, no credible behavioural change, inadequate preparation and positive abstinence tests.

## Consequences: What Happens When You Commit a Violation?

The consequences of a cannabis violation in road traffic are graduated.

### Administrative Offence under § 24a StVG (THC above 3.5 ng/ml)

First offence: 500 euros fine, 1-month driving ban. Second offence: 1,000 euros fine, 3-month driving ban. Third offence: 1,500 euros fine, 3-month driving ban. Additionally, 2 points are recorded in the fitness to drive register in Flensburg.

### Criminal Offence under § 316 StGB (Unfitness to Drive)

If, in addition to the THC detection, symptoms of impairment are present (swerving, causing an accident, reaction deficits in a fitness to drive test), a criminal offence of drunk driving may apply. The penalty ranges from a fine to up to one year of imprisonment, plus revocation of the driving licence for at least 6 months. A new licence can only be issued after an MPU.

### Endangering Road Traffic (§ 315c StGB)

If cannabis-related unfitness to drive creates a concrete danger to other road users or property of significant value, a conviction for endangering road traffic is possible. The penalty is up to five years of imprisonment.

## Novice Drivers and Probationary Period

For novice drivers in the probationary period (first two years after obtaining a licence), stricter rules apply. Even the first cannabis violation in road traffic leads to extension of the probationary period by two years, mandatory participation in an advanced training seminar and the regular fines and driving bans. For novice drivers under 21, a 0.0 per mille alcohol limit also applies – however, an analogous zero-tolerance rule for THC does not exist.

## Legal Remedies: What to Do After a Violation?

Anyone who receives a fine notice for cannabis in road traffic has several legal remedies available.

### Appeal Against the Fine Notice

An appeal can be filed within two weeks of delivery. Prospects of success exist particularly in cases of: procedural errors (e.g. faulty blood draw), analytical imprecision (measurement close to the limit – the measurement uncertainty is typically ±15 to 20 percent), lack of initial suspicion for the control and violations in evidence preservation.

### Lawyer

For cannabis traffic offences, consultation with a specialist lawyer for traffic law or criminal law is recommended. The costs (from approximately 500 euros) can pay for themselves many times over through avoided driving bans or MPU orders.

### Objection to MPU Order

An objection to an MPU order can be filed with the administrative court. The prospects of success depend heavily on the individual case. Since the KCanG, lawyers increasingly argue that the mere fact of cannabis consumption – without a traffic offence – no longer justifies an MPU, as cannabis is legal. Case law in this area is developing dynamically.

## Practical Tips for Cannabis Users

### Consistently Separate Consumption and Driving

The most important rule: do not consume and then drive. As a rule of thumb: after smoking cannabis, wait at least 12 hours before driving. For oral consumption (edibles), wait at least 24 hours. For regular consumption, these times may be considerably longer.

### Know Your Detection Times

If you consume regularly and drive regularly, educate yourself about your individual detection times. Some providers offer THC self-tests for blood or saliva that can provide rough guidance – but they do not replace forensic analysis.

### Behave Correctly During Controls

Stay calm and polite. Make no statements about your consumption behaviour – you have the right to remain silent. Refuse the voluntary preliminary test if you are unsure. Cooperate with the judicially ordered blood draw but request a judicial order. Do not let yourself be pressured.

### Document Everything

Note the date, time, location and course of the control. Remember the officers' service numbers. Note whether you declined or took the preliminary test. Request a copy of the medical documentation of the blood draw.

### Ensure Proper Insurance

Check your vehicle insurance: driving under the influence of drugs can lead to loss of insurance coverage. In the case of an at-fault accident under THC influence, the insurer can make recourse claims – which can cost tens of thousands of euros.

## Special Case: Medical Cannabis and Driving Licence

Patients with a medical prescription for cannabis are fundamentally allowed to participate in road traffic if they are fit to drive. The THC limit of 3.5 ng/ml does not apply to them in the same way: those who are properly adjusted and show no symptoms of impairment may drive despite higher THC levels. However, fitness to drive must be demonstrated in case of doubt, and a dosage change or start of therapy requires a waiting period until individual tolerability is established.

Patients should always carry the medical prescription in the vehicle and present it during controls. A positive drug test alone does not justify an administrative offence for patients – the decisive factor is actual fitness to drive.

## Outlook: How Might the Legal Situation Develop?

The combination of legalization and strict traffic regulation is criticized from many sides. Regular users argue that the limit effectively forces them to choose between cannabis consumption and driving. Legal scholars and toxicologists are discussing alternative detection methods that better reflect current impairment than a rigid blood value. Possible developments include: raising the limit to 5 ng/ml, introducing saliva-based rapid tests with legal evidentiary value, developing driving fitness test apps as a supplementary diagnostic tool and differentiating the limit for occasional and regular users.

Until then: anyone who wants to keep their driving licence must strictly separate consumption and driving – and stay informed about the current legal situation.