Criminal Lawyers for Positive Saliva Drug Test

Roadside saliva drug tests (also known as oral fluid screening devices) are the primary method used by Spanish police to detect drug-impaired driving. However, these preliminary tests have significant accuracy limitations and are subject to high rates of false positives. A positive saliva test does not, by itself, prove impairment—it only indicates the presence of certain substances.

Legal Framework: Technical Limitations

Key weaknesses include: cross-reactivity (over-the-counter medications, prescription drugs, and certain foods can trigger false positives), detection windows (cannabis metabolites can be detected for days after consumption, long after any impairment has ended), no correlation with impairment (a positive test shows substance presence, not that the driver's ability was affected), and environmental contamination (passive exposure to cannabis smoke can produce positive results). The offence of Art. 379.2 CP requires proof of actual impairment while driving, not the mere presence of a substance.

Defense Strategies

Our defense focuses on: demanding confirmatory blood or urine analysis (the preliminary saliva test alone is insufficient for conviction; laboratory confirmation is required, as the Supreme Court has held), challenging the chain of custody of samples, presenting medical evidence of prescribed medications that may explain the positive result, and arguing the absence of impairment signs (normal driving, passing field sobriety tests, no visible intoxication symptoms).

Presence vs Influence

Art. 379.2 CP punishes driving under the influence of drugs and, in any case, with a detectable presence. Where only presence is established —inactive metabolites with no current effect on the driver's faculties— the defence can argue that the offence is not made out and that the matter belongs in the administrative sphere. The argument turns on the principle of proportionality and on the external signs, or their absence, recorded in the police report.

Criminal Consequences

Drug-impaired driving under Art. 379.2 CP is treated like drink-driving: prison of 3 to 6 months, a fine or community service, and the deprivation of the right to drive of 1 to 4 years, with the prison term usually suspended for a first offence. Because a positive screening alone does not prove impairment and may reflect past, non-impairing use, the absence of confirmatory analysis or of clinical signs frequently leads to acquittal or to the reclassification of the matter as a mere administrative infraction.

Presence versus influence: the line between a crime and an administrative offence

This is the decisive distinction in drug-driving cases. The saliva test that the Guardia Civil or the police carry out at the roadside is an indicative screening test: it detects the presence of substances in saliva, but it does not measure how far they affect the ability to drive. The offence under Article 379.2 of the Criminal Code does not punish mere presence; it punishes driving under the influence of toxic drugs, narcotics or psychotropic substances. A positive saliva result therefore shows that the substance is in the body, not that the driving was actually impaired.

Where there is presence but no proof of real impairment of driving, what exists is an administrative offence under the Road Traffic Law (consolidated text approved by Royal Legislative Decree 6/2015), not a crime. The consequence is a financial penalty and the loss of points through the administrative channel, not a criminal conviction. That is why the defence always begins by separating the two levels: what a police report describes as an indicative positive is not, on its own, the influence required by the criminal offence.

The prosecution usually grounds influence on external signs recorded in the report: erratic driving, red eyes, slurred speech, lack of coordination. It is worth examining whether those signs were documented objectively and at the time, or whether they are generic impressions. The absence of concrete data of impairment, set against a simple positive for presence, is one of the central arguments for holding that the conduct does not cross the criminal threshold.

The evidential weight of the saliva test and the right to laboratory confirmation

The saliva test carried out on the road is an indicative screening, not a definitive item of incriminating evidence. A positive result opens the procedure, but it must be confirmed by a second analysis of a sample sent to a laboratory (saliva or, where appropriate, blood). That laboratory confirmation is what provides certainty about the substance and its concentration; without it, the roadside screening alone has limited weight to support a conviction.

The person subjected to the check has the right to request a contrasting analysis by means of a blood test, with the sample taken at a medical centre. This right matters because it allows the result of the portable device to be challenged, and because failing to allow it or to inform of it may affect the validity of the evidence. The defence reviews the chain of custody of the sample, the traceability from collection to laboratory, and correct identification, since any break may compromise the reliability of the result.

The screening device itself is also examined: its approval, its condition and the way it was used. An unapproved or improperly used indicative test proves nothing beyond the suspicion that justifies the next step. The key point is to remember that an indicative positive is the starting point of the investigation, not its conclusion, and that the decisive element is laboratory confirmation together with proof of influence.

Procedure: the police report, the fast-track trial and the guilty plea

Offences against road safety (Articles 379 to 385 of the Criminal Code) are a typical channel for the fast-track trials regulated in Articles 795 and following of the Criminal Procedure Act. After the check and the drawing up of the police report, the matter usually passes quickly to the duty court. Investigation falls to the Investigating Court or duty court, and the trial to the Criminal Court. Knowing this sequence makes it possible to prepare the defence from the first steps, which carry great weight in these cases.

In the fast-track trial a guilty plea is often offered, which may carry a reduction in the sentence requested. Whether to accept it is a decision that must be weighed carefully: a hasty plea, before reviewing the strength of the evidence (the indicative nature of the test, the lack of laboratory confirmation or the absence of data on real influence), may close the door to a defence with real prospects. The speed of the procedure should not mean giving up the chance to examine the report and the evidence.

For that reason it is essential to act as early as possible: study the report, check whether rights were respected during the check, assess the available evidence and decide, with proper judgement, whether a plea is advisable or whether to maintain the position at trial. The strategy is defined case by case, according to the specific evidence and the personal circumstances of the driver.

Penalties, driving ban, aggravating and mitigating factors, and limitation

A conviction under Article 379.2 is not limited to a prison term, a fine or community service: it always carries the deprivation of the right to drive motor vehicles and mopeds under Article 47 of the Criminal Code. In practice this ban is among the most burdensome consequences, because it bears directly on mobility and often on working life. Once the sentence has been served, recovering the licence may require further procedures.

It is also important not to confuse offences within the same group: refusing to undergo the legally established tests is a separate offence under Article 383, and driving after the licence has lost validity through total loss of points, or without ever having obtained one, is punished under Article 384. In assessing the penalty, aggravating circumstances (for example, factors of greater concurrent risk) and mitigating ones (such as making amends or the absence of a record) may carry weight, and are analysed case by case.

As to limitation, these road-safety offences carry a maximum penalty that does not exceed five years, so they become time-barred after five years under Article 131 of the Criminal Code. No shorter period applies: the applicable term is five years. Checking the calculation and the acts that interrupt it is a basic step in the defence, alongside the constant separation between the criminal offence and the administrative penalty under the Road Traffic Law.