Switzerland's THC limit: 1.5 µg/L blood

What does the limit measure?

The measurement is active Delta-9-THC in whole blood. 1.5 µg/L equals 1.5 ng/mL. The inactive metabolite THC-COOH – detectable for weeks after use – is not relevant.

The 1.5 µg/L threshold already factors in measurement uncertainty: reaching or exceeding it establishes unfitness on its own, no additional impairment proof required.

When am I back under the limit?

For occasional users, active THC in blood drops below 1.5 µg/L within 4–8 hours. Daily users can stay above the limit for 24–48 hours or longer – individual variability is high.

The safe rule is at least 24 hours before driving after a single session, and 72 hours for regular use. Home saliva tests offer no legal safety net – if in doubt, don't drive.

International comparison

• Germany: 3.5 ng/mL Delta-9-THC in blood serum (since August 2024).
• Austria: no numeric limit – individual impairment is assessed.
• France: zero tolerance – any positive trace is enough.
• USA (varies): Colorado, Washington, Nevada 5 ng/mL; some states zero tolerance.

Swiss practice: procedure, deadlines and costs

The 1.5 µg THC per litre of blood limit is not an impairment value but a determination threshold: it marks the point from which the laboratory considers the finding forensically secure. Legally, unfitness to drive is deemed proven at that value (Art. 2 para. 2 Traffic Rules Ordinance with Art. 34 VSKV-ASTRA) — no check of actual impairment takes place. In practice: even driving twelve hours after last use and feeling sober, a frequent consumer may still be above the limit because THC is stored in fatty tissue and slowly released. Only the blood sample taken by the forensic institute counts; the roadside saliva test is a preliminary test. Cost consequence of a positive blood sample: analysis and expert report of roughly CHF 900–1,500 charged to the driver, on top of the fine and the administrative measure.

The difference between preliminary tests and laboratory analysis

During traffic checks, the Swiss police frequently rely on so-called preliminary tests. These rapid saliva or urine tests serve the officers on site as an indicator to substantiate or refute an initial suspicion of cannabis consumption. However, a positive result in such a rapid test is not legally binding for establishing unfitness to drive. The rapid tests are often highly sensitive and can trigger even when the active THC level in the blood has already fallen below the critical limit. They merely serve as a decision-making aid to determine whether a blood sample should be ordered.

Only the chemical-toxicological analysis of a blood sample carried out by an authorized institute of forensic medicine has legal validity. Here, active delta-9-THC is determined using precise laboratory procedures such as gas chromatography-mass spectrometry. Only when this forensic report confirms the limit value of 1.5 micrograms per liter of blood is the unfitness to drive considered legally proven. Those affected must be aware that refusing an ordered blood test under Swiss road traffic law entails serious administrative and criminal consequences, which can be equated to a positive sample.

Risks of legal consumption: CBD and pilot projects in road traffic

In Switzerland, the consumption of cannabis products with a total THC content of less than one percent is legal, as they are not classified as narcotics under the Narcotics Act. Many consumers therefore lull themselves into a false sense of security when driving a vehicle. Even though CBD products can be legally purchased, they almost always contain small traces of THC. With regular or intensive consumption of CBD flowers, the THC they contain can accumulate in the body. In practice, this regularly leads to the limit value of 1.5 micrograms of active THC in the blood being exceeded during a traffic check.

A similar legal situation affects participants in the state-approved pilot trials in Swiss cities such as Zurich or Basel. Although the purchase and consumption of THC-containing cannabis is legalized within the framework of these scientific projects, no special regulations apply in road traffic. The Federal Office of Public Health (BAG) and the competent authorities always emphasize that participation in a pilot trial does not exempt participants from the strict rules of the Road Traffic Regulations. Anyone caught behind the wheel after consuming must expect the same harsh sanctions as any other road user.

Traffic-medical assessment and the reinstatement of the driving licence

If a person is found to exceed the limit in their blood, the authorities usually withdraw their driving licence as a precautionary measure. In order to regain driving aptitude, the cantonal road traffic offices generally require a traffic-medical assessment. This procedure serves to rule out chronic abuse or dependency. The assessment is carried out by recognized traffic medicine specialists and includes a physical examination as well as a detailed discussion about consumption habits and the personal life situation of the person concerned.

A central component of this assessment is proof of stable abstinence, which must usually be provided via hair analysis. Since THC metabolites are incorporated into the hair as it grows, consumption can be reconstructed seamlessly over months. As a rule, the authorities require documented proof of abstinence of at least six months, and in severe cases even one year, before a reassessment takes place. All costs for the traffic-medical examinations, laboratory analyses, and administrative fees must be borne by the individuals themselves.

Cantonal differences in enforcement and police checks

Although the Traffic Regulations Ordinance and the limit of 1.5 micrograms of THC per litre of blood apply uniformly throughout Switzerland, clear cantonal differences exist in practical enforcement. The density of police checks and the awareness of emergency services vary greatly between urban agglomerations and rural regions. The handling of suspicion and the thresholds for ordering a blood sample are also interpreted with varying degrees of severity by the cantonal police forces. Some cantons increasingly rely on modern saliva testing devices, while others primarily trust classic pupil and coordination tests.

These cantonal discrepancies are also reflected in the handling of minor offences. Although federal law provides for a fixed penalty of CHF 100 for adults with small quantities of THC cannabis, the linking of these offences with road traffic law is handled differently from canton to canton. If cannabis is found on a person during an identity check without them driving a vehicle, some cantons systematically report this to the road traffic office to assess driving aptitude, while others refrain from doing so. Consumers should therefore be aware of the strict practices in their respective canton of residence and driving.

How long is THC detectable in the blood after consumption?

In blood, active THC is usually detectable for between 4 and 8 hours in occasional users, but in regular users, detectability can last for several days. The exact duration depends heavily on individual metabolism, body fat percentage, and frequency of consumption. Since THC accumulates in fatty tissue and is slowly released back into the bloodstream, daily users can still exceed the limit of 1.5 micrograms per litre of blood even after days of abstinence.

Can the police force a blood sample without suspicion?

No, the police may not order a blood sample without reasonable suspicion of unfitness to drive. There must be concrete signs such as conspicuous driving behaviour, red eyes, delayed reactions, or a positive preliminary test. However, if a driver refuses a reasonably ordered saliva test or blood sample, this is legally considered an evasion of measures to determine fitness to drive, which entails penalties of similar severity to a positive blood sample.

Does the THC limit also apply to riding e-bikes?

Yes, the THC limit of 1.5 micrograms per litre of blood also applies to riding e-bikes and bicycles in Switzerland. Since cyclists, as road users, are subject to the rules of the Road Traffic Act, they must expect sanctions in the event of unfitness to drive. Although non-motorised vehicles do not usually carry the threat of direct revocation of a driver's licence for a first offence, the authorities can issue a ban on riding bicycles and, in the event of doubts about general fitness to drive, order a traffic medicine assessment.

Riding home on two wheels also requires fitness to ride. Our guide explains the differences between ordinary bicycles, slow e-bikes and faster models: Cannabis on bicycles, e-bikes and e-scooters: Swiss vehicle classes and consequences

How does medical cannabis affect fitness to drive in Switzerland?

Even with a medical prescription for medicinal cannabis, the strict zero-tolerance limit of 1.5 micrograms of THC per litre of blood generally applies to Swiss road traffic. Patients are only permitted to drive a vehicle if a traffic medicine assessment has positively confirmed their fitness to drive under the specific medication. Even with such an assessment, fitness to drive must be critically evaluated individually before every journey, as the responsibility for safe participation in road traffic always remains with the driver.

Frequently asked questions

Does CBD count toward the THC limit?

CBD itself is not counted. But legal CBD flower contains up to 1.0 % THC – heavy use can still push you over 1.5 µg/L.

Can I drive on medical cannabis?

In principle no – zero tolerance applies even with a prescription. Exceptions require an individual medical fitness assessment.

What if the blood test shows 1.4 µg/L?

Below 1.5 µg/L the zero-tolerance rule does not automatically apply. Police must then prove concrete signs of impairment (driving, physical state).

Who pays for the blood analysis after a positive check?

The driver. Analysis and toxicological report together cost roughly CHF 900–1,500, on top of the fine and the administrative measure.