THC testing in blood and saliva and driving

We've known it for a fact: the zero-sum approach of current laws to the issue of acceptable THC concentrations in drivers' blood is flawed. A recent meta-regression study conducted in Australia provides unequivocal evidence. It turns out that mere information about the concentration of THC in the body is definitively not the same as an impairment of driving ability. What is clear, however, is that neither the medical use of cannabis nor the announced decriminalisation of cannabis can mean a reduction in road safety. Can this somehow be reconciled?

What is the situation today? What are the risks for drivers who are medical cannabis patients or consumers of legal and illegal cannabis products? Is anyone doing anything about it? What solutions are being proposed? What does scientific research say about THC limits? What solutions might the future and technology bring? I invite you to read on.

Read in: 6 minute(s)

Status of hemp and cannabis in Polish law

The current cannabis law is unambiguous at this point:

  • The cultivation, possession and trafficking of recreational cannabis is prohibited and punishable by imprisonment,
  • The use of medical cannabis is legal for patients as a medicinal product dispensed in a pharmacy with a doctor's prescription,
  • Seed cannabis with a THC content of less than 0.2% is legal and publicly available.

In the context of driving, both patients of legal medical cannabis and users of tetrahydrocannabinol cannabis products bear risks.

The drug tests used by the police during routine checks are quite sensitive. Already after about 15-20 seconds, a positive test result from saliva collection can indicate a serious problem. It is standard at such a point that the driver is referred for a forced blood (or urine) test to confirm the saliva result with a more precise test that determines the THC concentration in the body.

The issue is getting sad.

There is no way of testing whether the driver actually has impaired consciousness and driving ability. There are neither regulations nor accepted, proven methods for this, and at least none of the potential candidates for such a method are currently being seriously considered in our country.

More about this later in the article.

Under the influence, and after use - there is a difference!

It is estimated that up to 1 million drivers travel on Polish roads every day while being 'after using' a THC drug.

It is difficult to imagine that even in today's Poland, someone would come up with the idea of mass criminalisation of such a huge number of citizens. This seems all the less likely as we are civilisationally one step away from decriminalising the possession of small quantities and personal use of recreational cannabis. It is rumoured that Mr Paweł Kukiz has reached an agreement with President Jarosław Kaczyński on this issue.

This does not change the fact that bringing about a clear definition and distinction of the concepts of 'state of under the influence of intoxicant' and 'state of after use intoxicant" is simply necessary and unavoidable.

Just so there is no doubt, let me be clear: I am an enemy of driving under the influence of anything that impairs cognitive ability, delays reaction time, distracts or materially adversely affects the ability to make a rational judgement on the road.

Permitted concentration of THC in the driver's blood

In the Polish legal system, there is no such thing as a permitted concentration of THC in the body as there is in the case of alcohol testing.

A zero-one driver found to have a trace amount of Delta-9 THC risks losing his or her licence and incurring all other criminal liability consequences prescribed by law.

This is the case even when the source of the psychoactive cannabinoid is legal medical cannabis used for health purposes as a medicine or when the tested concentration exceeds only 2.5 nanograms of THC per millilitre of blood [ng/mL].

The 2.5 ng/mL is the blood THC level used in court jurisprudence, not resulting from legislation but from the practice of forensic experts, the exceeding of which automatically gives the situation the hallmarks of a criminal offence.

Below this threshold, the courts declare an offence. The consequences are still very severe in such a case and include periodic loss of the driving licence and heavy fines.

The problem is that a mere determination of concentration is not evidence either of intoxication or, even less, of a reduction in road safety. Such evidence is basically only proof of a driver's cognitive impairment impairing their ability to drive safely.

At this point, it is worth reassuring those using e.g. CBD oils. The risk of detecting tetrahydrocannabinol in saliva already about 1-2 hours after taking an after all small dose of a few drops of the preparation is practically zero. If the saliva drug test shows nothing, and the circumstances do not indicate otherwise, the police officer will not refer for a confirmatory test from blood or urine.

thc testing in blood in the laboratory

Will this ever change?

Happily, awareness of the need for change in this area exists among the pro-legalisation community and politicians involved in the depenalisation and legalisation processes of cannabis.

Particularly noteworthy and commendable in this regard are the position and actions of Mr. Jarosław Sachajko from KUKIZ'15.

Unfortunately, the interpellation that this politician submitted on the issue of the THC limit for drivers to the Ministry of Health lived to see a classic response, which in a nutshell shows that the MZ is not dealing with the issue and has no plans to do so in the foreseeable future. This is a pity.

The Ministry overlooks existing solutions in the world, erroneously claiming that the current state of scientific and practical knowledge makes it impossible to set a limit or at least a range of such values at all.

And what is it really like?

Such solutions exist in the United States, Norway or Denmark, among others.

The literature of published, peer-reviewed scientific research includes, among other things, highly valuable studies using realistic car driving simulators in various road conditions.

There are studies that make it clear that blood concentrations of Delta-9 Tetrahydrocannabinol are not at all a reliable measure of driving impairment, or even of the cognitive functions necessary for driving.

Serious publications can also be found showing that there is no increased risk of accidents in drivers with labelled THC levels of 2-5 ng/mL.

Alcohol vs Marijuana

The analogy between alcohol and cannabis is apparent and, as usual, the devil is in the detail.

Differences between alcohol and cannabis appear already at the level of toxicokinetics. Intoxication by the two substances has a different nature, course, duration and intensity and extent of cognitive impairment.

In the case of alcohol, we know with 100% certainty that the higher the blood concentration, the stronger the intoxication.

This principle does not work with cannabis, where the peak intoxication occurs around 60-90 minutes after use, i.e. when the concentration is already in decline, and the cessation of intoxicating effects passes within 4-6 hours. To be on the safe side, experts suggest waiting about 10 hours.

Australian study of the effects of THC on driving ability

9 November 2021 on Neuroscience & Biobehavioral Reviews available online at Science Direct (link in sources below the article), the results of a regression meta-analysis by a team of researchers from the University of Sydney led by Dr Danielle McCartney have been published.

What makes this study different from others?

Well, metaregression is a method of ordering and evaluating a set of existing scientific studies. It enables a kind of synthesis of the results of heterogeneous research by facilitating the use in practice of compiled knowledge stemming from numerous, historically stretched works on a given issue.

One might be tempted to say that this one study replaces all previous ones.

What can we learn from the scientists this time?

  1. THC biomarkers are not associated with impairment of [KD: driving ability and cognitive functions used while driving] in individuals regularly cannabis users
  2. THC biomarkers have a weak association with impairment of [KD: steering ability and cognitive functions used while driving] in individuals occasionally cannabis users
  3. THC biomarkers are generally relatively poor indicators of impairment [KD: steering ability and cognitive functions used while driving].

In the conclusion of the publication, the authors pointed out that the use of THC concentration limits could lead to the criminalisation of people whose cognitive functions and ability to drive safely are not impaired in any way.

Interestingly, the authors indicate that the medical use of cannabis may even improve the ability and cognitive function necessary for safe driving in patients treated with medical cannabis for, for example, insomnia or chronic pain.

Of course, under no circumstances we do not say about the situation of driving "under the influence", i.e. when the driver is simply intoxicated.

Doesn't this mean that the concept of a THC limit for drivers should be considered useless in general and therefore any parliamentary efforts in this regard are pointless?

Was there cognitive impairment or was there not?

To answer the question about the point of using limits in THC blood tests, it is worth remembering that it is good to have such a rigid or range-defined parameter on your side of the power.

Setting the Delta 9 THC limit at a responsibly high level could help save a lot of time, money, energy, stress and hassle for non-road-hazardous drivers. The courts, I imagine, would also be fine with a solution that minimised the number of cases while not risking increasing the danger on Poland's roads.

At the end of the day, this is what safety is supposedly all about, not callously raising crime statistics and recapitalising public funds with fines. Yes or no?

What if the concentration limit is exceeded? As we already know, this does not prove intoxication combined with impaired driving.

What could provide such evidence? Innovative technological solutions can help.

I think we will soon see concrete proposals for e.g. smartphone apps based on artificial intelligence algorithms.

Since we can perform tests that unambiguously assess our psycho-motor state based on a set of observations of, for example, pupil reaction to light, reaction time or divided attention, I bet dollars against nuts that artificial intelligence and two pinches of hardware can also learn this with enough precision to constitute irrefutable proof of guiltlessness.

Mobile apps for use by medical cannabis patients, consumers of legal cannabis products and, in the longer term, recreational cannabis users, in my opinion, have the power to solve the problem while maintaining high safety standards on Polish roads and beyond.

Implementing such solutions would require significant changes to the law.

It is more than certain that somewhere in the world someone is currently working on solutions to the problems addressed in this article.

I quietly hope that we will see the time when this multitude of non-risk drivers will stop driving with the proverbial soul on their shoulders, and when THC testing in the blood will no longer be a cause for panic.

Driving and THC through the eyes of a police officer

Very interesting material on driving a THC in the form of a podcast to listen to has been made available on its website Opening Eyes activist and figure fully deservedly gaining a wider and wider audience in the cannabis world - Matthew Zbojna. In one of the episodes, which you can listen to below, Matthew spoke to Police Activist namely Kamil Kaczorowski - a man who, by virtue of his profession and his experience with the use of medical marijuana, is perfectly familiar with the procedures for the practical application by the police of Poland's current drug laws during roadside checks.


  3. - The legal blog of Stelios Alewras - drug lawyer and pro-legalization activist
Pure Hemp Shop - Trusted
SEMIKO sp. z o.o. Reviews with

We use cookies to continuously improve the quality of our services, our commercial offer and to enrich our content. You can find out more about this and how we process your personal data in our PRIVACY POLICY.

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.