Cannabis and driving: controversy rages on

It is well known that the time taken to flush the remains (metabolites) of cannabis from the body of the person who has used it is much longer than for any other substance detectable in a check (alcohol, amphetamines, benzodiazepines, cocaine, MDMA, methamphetamine, and opiates). While alcohol disappears from the body within a few hours and stimulants take three to four days, some people test positive for cannabis up to three weeks after their last use. A number of factors will have a bearing on the rate of elimination; for example, whether the person is an occasional or regular user, or depending on their weight and the amount of fatty tissue they have as this is where the metabolites are stored and slowly released.

Furthermore, as more countries roll out cannabis access programmes (for medical or adult-use), various regulatory models for drug testing and driving are being put forward. If you compare these proposals with countries where there are no cannabis access laws, it is easy to see that there is a lot of work to be done before we can claim to understand the basics of how cannabis affects driving. Today, ‘zero tolerance’ policies stand side by side with policies that are very tolerant of use. The challenges for the future are to scientifically determine the thresholds above which driving is dangerous; make progress in the specificity, sensitivity and reliability of testing; work on the quantitative determination of consumption, and try to filter out false positives which may result from past consumption.

On a more down to earth level, and aside from theoretical considerations and legal debates, there is the current Road Traffic Act which penalises a positive test result and also the effect of cannabis on driving. Below is a summary of its most relevant points together with a rundown on some scientific publications which may help to provide some context for this fascinating debate and its implications.

We start from the underlying assumption that cannabis use affects us in several ways: perceptively (senses), cognitively (memory, attention, etc.) and in psychomotor terms (response time, coordination of movements, etc.). Cannabis’s influence on driving varies depending on the amount consumed and how long it is since it was consumed. It is also acknowledged that people who use cannabis regularly are less affected than those who do so occasionally, unless they combine it with drinking alcohol as this increases the risk of having an accident.

Drug testing is a highly controversial issue around the world. In fact, as is the case with alcohol, each country takes a different approach. In Spain, a breathalyser is used to determine how drunk the person is and a different instrument, the ‘Drogotest’ drug test (also known as a ‘lollipop’), is employed to detect the presence (or not) of metabolites in saliva as a result of the ‘digestion’ of the various psychoactive substances that the person has swallowed.

Under section 14 of the Road Traffic, Motor Vehicle and Road Safety Act, ‘the driver of any vehicle may not drive on the roads covered by this Act with the presence of drugs in their body, excluding any substances used under medical prescription and for therapeutic purposes and provided that they are able to drive the vehicle in keeping with the duties of diligence, care and avoidance of distraction’. In addition, ‘the driver of a vehicle is required to submit to tests for the detection of alcohol or the presence of drugs in their body’. In other words, refusing to take the tests is an offence involving disobedience to authority and the penalty can be between six months and one year’s imprisonment and disqualification from driving for a period of one to four years.

If you test positive in a control and the law enforcement officers consider that you are not driving under the influence of the substance, this would be an administrative offence which would entail:

─Losing six points off your licence.
─A €1,000 fine (reduced by 50% if paid within a fortnight of notification).
─Possible immobilisation of the vehicle (at the discretion of the authorities).

If there is a positive result in a control and in this case the law enforcement officers also consider that one of these situations applies:

─The person is driving under the influence of the substance or there are clear signs.
─An offence may be related to the use of the substance.
─The person has been involved in a traffic accident.

These cases would constitute a criminal offence, which would entail:

─The immobilisation of the vehicle.
─The authorities would draw up a report.
─Three to six months’ imprisonment or a day-rate fine lasting six to 12 months or community service.
─Withdrawal of driving licence for one to four years.

How is a drug test carried out?

  1. It begins with taking a saliva sample, a procedure consisting of two steps. The first, known as an indicative test, is used to detect the presence of illegal substances. If this first test gives a positive result, the second test, known as the evidential test, is carried out immediately afterwards to identify the type of substance and its quantification. If this second test is also positive, the driver may no longer drive their vehicle, which will be immobilised.
  2. At the same time as the saliva sample is taken, the officer assesses the driver’s external signs which may influence driving such as nervousness, trembling, etc. These signs are added to the case file for the proceedings. This assessment will be crucial as it makes the difference between an administrative fine and an action constituting a criminal offence.
  3. After the second positive result (the evidential test) and before leaving the checkpoint, the driver may ask for a blood test to confirm the data provided by the saliva sample. This will be carried out by medical staff in a hospital. If the results are also positive, the applicant has to pay the costs of these tests.
  4. The saliva samples (and blood samples if requested) are sent to a laboratory. The security measures in the transfer are extremely strict: the samples are transported in sealed tubes, in sealed coolers, in vehicles specifically designed for carrying biological samples, etc. There also has to be a chain of custody to ensure that the evidence collected is not altered or tampered with in any way.
  5. When the containers get to the laboratory, specialised staff check the security conditions have been met, empty out their contents, and all the documentation is checked with a record made of the date and time of receipt. The samples are then registered and ready to be analysed.
  6. The analysis is carried out using a gas chromatograph and a mass spectrometer, which will determine what kind of drug is in the sample and the quantity.
  7. The results are validated one by one by specialised medical staff. The complete final report will be sent to the local Traffic Department (Prefectura de Trànsit) for further processing.

You can lodge an appeal against a fine with the relevant government agency. However, if you do decide to appeal, it is unsuccessful and you end up having to pay the fine, you will not be eligible to get the 50% off for prompt payment. In 2018 a court in Oviedo ruled in favour of a driver fined for testing positive for cannabis as it found that the administrative procedure carried out had infringed a number of fundamental rights which directly violated the right of defence that every person is entitled to.

Remember that there are several factors which determine how long cannabis metabolites stay in the body: a) the amount of the substance consumed, b) the type of consumption: whether it is occasional or recurrent, c) each person’s metabolism (each individual’s rate of elimination) and d) the presence of other illnesses or health problems.

Some studies suggest that THC lasts for 12 hours in saliva, although others estimate it at two or three days. Meanwhile, in blood it is up to four days (approximate values) for occasional use and up to seven days in the case of recurrent use.

The drug use test also does have a cut-off point, i.e. a specific quantity above which it tests positive. The device used in Spain is usually the Draeger Drugtest 5000, which tests positive for cannabis at 5 nanograms of THC. The Alere DDS2 model is also employed, although we do not know its technical specifications.Final del formulario

Cannabis metabolites build up in our body’s fatty tissues, which is why they are flushed out much more slowly than, for example, alcohol, cocaine or MDMA. This means that an overweight person who smokes regularly would need much more time to purge their body of THC than a slim person who only smokes occasionally. Physical exercise is another important factor. One study has shown that THC levels (urine) are considerably lower when tested immediately after exercise.

You should additionally be aware that in the event of an accident, insurers do not have to pay any costs or provide any coverage if the test is positive. In other words, they are released from all obligations under the policy.

As for CBD, if the product consumed is pure and does not contain THC, it should not test positive in the ‘Drogotest’ because it is not a psychoactive substance. However, the problem is that it is legal in today’s market to mix CBD with THC (at most 0.2%), and in this case it might test positive for THC in a control.

The scientific evidence on the likelihood of having more accidents when driving under the influence of cannabis is mixed. Most studies are research conducted with driving simulators and/or using neuropsychological tests of psychomotor performance coupled with survey-based studies.

In 1998, a field study was performed in Germany outside discotheques with 241 subjects who had taken drugs and were going to drive or had driven a car at the time. Using a simulator with a laptop computer and a joystick, the volunteers had to hold a car in the middle of a lane while driving along a winding road with an 80 kph speed limit. Blood and saliva samples were also taken. It was found that cannabis or ecstasy/amphetamine use alone did not adversely affect driving performance, although the combination of the substances with one another and/or alcohol did. However, the sample of cannabis users was only 39 subjects and the simulator probably lacked ecological validity.

A meta-analysis published in 2012 which compiled all the studies published to that date did not find any consensus about whether the risk of crashes is higher or lower under the influence of cannabis. In a more recent study conducted in a laboratory setting, 80 volunteers were given different doses of THC and alcohol (40 for THC and high alcohol and 40 for THC and low alcohol), using a simulator that reproduced real-life conditions fairly closely. Again, the combination of THC and alcohol was found to impair driving ability, with a higher incidence under night-time driving conditions in both regular and occasional cannabis users. It also confirmed the results of previous research that the combination of alcohol with cannabis increases THC concentrations in the blood. The researchers reported that despite differences between groups in test performance, the overall degree of impairment in all treatment conditions was slight. Moreover, as this was an exploratory study, further studies are needed to confirm its findings.

A 2015 study, which did not use a driving simulator but rather neuropsychological tests as indicators of possible psychomotor impairment in driving, found that occasional cannabis users performed worse on tests under the effects of THC than frequent users, suggesting that there is a possibility that frequent users may develop some tolerance to the psychomotor effects of cannabis. THC-impaired driving was also found to be dose-dependent, i.e. the higher the dose of cannabis, the greater the driving impairment.

In another study, conducted with 75 subjects aged 18-25 years who had reported using cannabis at least once in the past 12 months, both self-reported driving under the influence of cannabis (DUIC) and objective effects were studied in a simulator under normal conditions (without cannabis administration). The finding was that cannabis users self-reported a risky driving style, including a broad range of reckless on-road behaviour. A higher rate of reckless behaviour was also found in the simulator test. However, these results may have more to do with the specific population studied (18-25 years) or with a self-selection problem of the sample: as the simulation was conducted under normal conditions (no cannabis administration), the results may be due more to a specific personality style of the sample studied than to the fact of being a cannabis user. Indeed, a study reviewing the major research, both laboratory-based and epidemiological, concluded that because drivers who have used cannabis are more aware that their abilities are impaired, they tend to compensate effectively for the impairment by using a variety of behavioural strategies such as driving more slowly, overtaking less and leaving more space between themselves and the cars in front of them. It is also found that the combination of marijuana and alcohol eliminates the possibility of using these strategies effectively.

What one study did say is that under the acute effects of cannabis, the ability to multitask worsens, which means that driving could be impaired. A 2018 study concluded that regular cannabis users had slower reaction times, deviated less in speed and had greater difficulty matching a lead vehicle’s speed compared to non-users.

In short, the easiest way to avoid testing positive in a drug test if you have consumed cannabis is not to drive. If you do have to drive, it’s best to leave more time between your last use and driving. Your own and other people’s safety are worth more than any traffic ticket. The relationships between marijuana use and driving accidents are not yet fully clear and studies should be conducted using larger samples, comparing performance on simulators between frequent and infrequent users, stratifying by age and gender, and controlling for variables such as alcohol and/or other drug use.