Police saliva test – how it works

TL;DR

• Roadside cassette test (e.g. Dräger DrugTest 5000), result within ~5–10 min.
• Positive result: mandatory blood draw at hospital or by an official doctor.
• Only the blood value is admissible – the saliva test is a pre-screen.
• Refusing the saliva test leads directly to a mandatory blood draw.

Step-by-step procedure

On reasonable suspicion (driving, smell, red eyes, admission), police order a saliva test. A swab is placed in the mouth for 1–2 min; the cassette reads THC (and other drugs). Cutoff ~25 ng/mL.

If positive, a blood draw follows (BÄK guidelines) – mandatory, refusal is a criminal offence. A forensic institute performs the analysis.

How a roadside check runs: preliminary test, blood draw and the 1.5 µg/L limit

The roadside saliva test is a preliminary test under Art. 55 SVG. It only indicates whether active THC is detectable in the oral cavity – an indication, not a measurement. If it is positive, or if you refuse it, the police order a blood draw performed by a physician and analysed at an institute of forensic medicine. Only that blood value decides the case.

Switzerland applies a legal THC limit of 1.5 µg/L in blood (Art. 2 para. 2 VRV together with ASTRA guidance). Above it, unfitness to drive is deemed proven without any driving error having to be shown. Consequences are typically licence withdrawal, a fine or a monetary penalty and, depending on your record, a fitness assessment with abstinence monitoring. A prescription for medical cannabis does not automatically exempt you; the cantonal road traffic office must assess the case individually.

The legal framework in the Road Traffic Act

The conduct of drug tests in Swiss road traffic is based on clear legal requirements in the Road Traffic Act. According to Article 55 SVG, the police are authorised to order measures to determine unfitness to drive in the case of drivers if there are corresponding indications. The saliva test serves as a quick, non-invasive tool for pre-selection directly on site. However, it does not constitute definitive evidence for court proceedings, but merely provides the officers with the reasonable suspicion that is mandatory for ordering further, more invasive measures.

Should the preliminary saliva test be positive, the legal chain of action for the authorities is mandatory. The police must order a blood sample, which may only be taken by a medical professional. This two-stage system protects the rights of those affected against faulty rapid tests and ensures that serious legal consequences are only decided on the basis of highly precise laboratory medical analyses. The coordination between the police, medical institutions, and the cantonal road traffic offices is strictly regulated.

• Legal anchoring of control powers in Article 55 of the Road Traffic Act.
• Function of the saliva test purely as an instrument for establishing suspicion without direct evidentiary value.
• Mandatory requirement for a medical blood draw following a positive preliminary test result.
• Protection of the individuals concerned through the requirement of forensically precise laboratory analyses.

Detection windows and biological influencing factors

The detection window of tetrahydrocannabinol in saliva differs fundamentally from that in urine or blood. While urine tests primarily detect inactive metabolites that remain detectable for weeks, the saliva test mainly detects active THC that is deposited in the oral cavity during consumption. As a result, the detection window in saliva is comparatively short, usually spanning only a few hours after the last consumption. Nevertheless, individual factors such as salivary flow, oral hygiene, and the method of consumption can influence the result.

With regular consumption, THC can also accumulate in saliva with a time delay due to redistribution processes in the body, making predictability more difficult. In addition, modern testing devices are highly sensitive to the smallest traces. Passive exposure in smoky rooms does not generally lead to the limit values being exceeded, but it can trigger a positive result at the threshold under extreme conditions. Since individual biology varies greatly, there is no reliable formula to predict the exact duration of detectability in saliva for an individual case.

• Detection of active THC in the oral cavity instead of long-term metabolites.
• Typical detection window of a few hours after the last active consumption.
• Influence of individual physiology and frequency of consumption on the retention period.
• Low risk of positive findings through purely passive consumption under normal conditions.

The administrative procedure of the road traffic offices

A positive saliva test, if subsequently confirmed in the blood, triggers a dual-track procedure. Alongside the criminal proceedings, which end in fines or monetary penalties, the competent cantonal road traffic office initiates administrative proceedings. These proceedings deal exclusively with the affected person's fitness to drive. Since Swiss law irrebuttably presumes unfitness to drive if the limit of 1.5 micrograms of THC per litre of blood is exceeded, there is an immediate threat of the driving licence being withdrawn as a precautionary measure.

To regain the driving licence, the authorities generally require a traffic-medical assessment. During this evaluation, the affected individuals must prove that there is no substance use that precludes fitness to drive. This usually requires proof of stable abstinence over several months through urine or hair analyses. The costs for these comprehensive medical assessments and laboratory analyses are extremely high and must be borne entirely by the affected person, representing a significant financial burden.

• Strict separation between criminal sanctions and administrative withdrawal of the driving licence.
• Immediate precautionary withdrawal of the driving licence if the blood limit is exceeded.
• Necessity of a traffic-medical assessment of fitness to drive for reinstatement.
• Assumption of all incurred assessment and laboratory costs by the affected driver.

Distinction from CBD and medical cannabis

The legal liberalisation of CBD products in Switzerland often leads to consequential misunderstandings in road traffic. Although CBD cannabis with a total THC content of less than 1 per cent is not classified as a narcotic and is legally available, it still contains small amounts of THC. Anyone who consumes CBD regularly or in large quantities risks the THC accumulating in their body. This can result in a positive saliva test during a roadside check, as well as exceeding the legal blood limit of 1.5 micrograms per litre.

Even for patients who have been prescribed medical cannabis by a doctor since August 2022 without an FOPH exceptional permit, no special rights apply in road traffic. The zero-tolerance practice regarding unfitness to drive remains in place. A medical prescription does not protect against the consequences of a positive drug test. In such cases, the road traffic office assesses on an individual basis whether safe participation in road traffic is guaranteed under the medication regimen, with strict traffic-medical requirements and regular checks being the rule.

• Risk of accumulation of THC traces in the body due to the consumption of legal CBD.
• No distinction made by rapid tests between legal CBD and illegal cannabis.
• Continued existence of strict limits even in the presence of a medical prescription.
• Case-by-case assessment of the fitness to drive of medical cannabis patients by the authorities.

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