With the advent of the new Highway Code there is a lot of talk about drugs that can influence the results of drug tests during a roadside inspection. There is even the story of a driver who had his license revoked for taking a Tachipirina. Let’s clarify right away: this is a false myth! Drugs based on paracetamol, the active ingredient contained in Tachipirina®, they cannot interfere with drug tests salivary or urinary tests and even less so with the alcohol test, therefore their intake does not lead to the withdrawal of the driving licence. But there are some drugs, like antidepressants and some over-the-counter medications, such asibuprofen and other non-steroidal anti-inflammatories (NSAIDs) which may, in rare cases, give rise to a false positive.
If I take ibuprofen or paracetamol, can my license be taken away?
The answer is no. As for paracetamol, there are no studies reporting false positives in drug or alcohol tests caused by this molecule and does not affect driving ability. The same leaflet for paracetamol-based drugs under the heading “Driving precautions” contains the words “It does not affect the ability to drive or use machines”. The only exception, if we really want to be picky, are painkillers based on paracetamol and codeine, but in this case it is the codeine that gives positivity, given that it is an opioid drug: in fact they are subject to various controls and can only be purchased with non-repeatable medical prescription (RNR).
For ibuprofen, however, cases of false positives have been reported for i cannabinoids and in some cases even for the phencyclidine (aka, PCP), a powerful hallucinogenic. One wonders: how much ibuprofen can give a false positive? There is no single answer. A clinical study from the 1990s tried to make this complex calculation by drug testing volunteers who took different doses of ibuprofen and other anti-inflammatories. Long story short, they collected 510 urine samples and only TWO were false positive results for cannabinoids.

So you can rest assured: if you take a painkiller or an anti-inflammatory, you will have a very low probability of testing positiveif they ever had to stop you. This data is also confirmed by a study by the Papa Giovanni XXIII Hospital of Bergamo, which used one of the devices supplied to the police, the Abbott SoToxa. The Bergamo study, carried out on SerD patients (Pathological Addictions Service) has in fact detected very few cases (7 out of 292) of false positives to amphetamines, however caused by antihypertensive, hypoglycemic and mood stabilizing drugs.
Driving license withdrawal and drugs: which can cause false positives
A false positive is obtained when the test gives a positive result for the presence of a substance, even if it has not been used. There are a few things that cause these false positives drugssometimes even very common, or some foods, such as poppy seeds which, if eaten in excessive quantities, could test positive for opiates (after all, opium and morphine derive from Papaver somniferum).

It is not yet clear how this interference occurs: according to some authors it is caused by a structural similarity between these molecules and the illegal substances sought, while in most cases the cause of theinterference remains unknown.
The first case includes drugs based on pseudoephedrinea molecule contained in many nasal decongestants, from products for allergies to those for rhinitis. If this name sounds familiar, you’ve probably seen Breaking Bad! The “pseudo” is in fact used in the show as precursor of methamphetamine synthesis and you will remember Jesse Pinkman trying to get as many rhinitis drugs as he could, before Professor Walter White proposed another method, faster and with greater yield. But that’s another story.
In addition to pseudoephedrine, also some classes of antidepressantssome antipsychotics, such as quetiapine and the unsuspected ibuprofenand other NSAIDs, have caused false positives, primarily in rapid urine drug tests. Antidepressants and antipsychotics are, however, drugs for which a medical prescription is required, while ibuprofen is a very common over-the-counter drugbut as we have seen these are very rare cases.
What are drug tests and how do they work
Rapid salivary and urinary tests often used as screening by the police are a very useful, fast and minimally invasive to analyze biological fluids for substances of abuse, mainly cocaine, amphetamines, methamphetamines, opiates, ecstasy and cannabis (THC).
The most common ones exploit the immunological methodsuch as for pregnancy tests or COVID-19 tests, in which specific antibodies immobilized on the support bind to illegal substances if present in the saliva or urine sample taken. The tests used by the Police and Carabinieri are the Sotoxa devices from the Abbott company and the DrugWipe S respectively.
Obviously, although with high percentages of precision, these tests are not infallible and can give false negative or false positive results. It must be said that these are mainly tests qualitative which are followed by specific quantitative tests laboratory, as confirmed by the Italian Forensic Toxicologists Group and in any case, the percentages of false positives are very low.
However, it seems that there are some problems with the tests supplied: first of all, according to what was declared by the companies, the DrugWipe S detect a minimum limit of 10 ng/ml of delta-9-tetrahydrocannabinol (THC, the active ingredient of cannabis), while Sotoxa devices have a limit of detection at 25 ng/mlthus creating possible discriminations based on the device with which the analysis is carried out. Another critical issue was also identified by the study by the ASST of Bergamo: the Sotoxa devices they do not detect important substances of abuselike the fentanyl and the methadone.
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