Driving under the influence of medication: when is it an offence?

Driving under the influence of medication is a criminal offence in Belgium as soon as a medicine puts you in a state comparable to drunkenness, or when a saliva or blood analysis shows a substance from the statutory drugs list above the threshold. A medical prescription is not an automatic exemption. Below, we explain which rules apply and what you should do during a roadside check.

Drugs and medicines: two different rules

The Road Traffic Act (Wegverkeerswet / loi relative à la police de la circulation routière) works with two systems. Article 37bis is a so-called presence rule: it is sufficient that a saliva or blood analysis shows one of the listed substances at a concentration equal to or above the statutory threshold.

Article 35 works differently. It punishes anyone who drives a vehicle while drunk or in a similar state, in particular as a result of the use of drugs or medicines. Here everything turns on your actual condition, which the police establish on the basis of your behaviour and outward signs.

In addition, Article 8.3 of the Highway Code (Wegcode / Code de la route) provides that every driver must be in a fit state to drive and must have the required physical fitness and the necessary knowledge and driving skills.

Which substances are on the Article 37bis list?

The list currently contains five substances or groups of substances. The thresholds are set out in Articles 61bis (saliva test), 62ter (saliva analysis) and 63 (blood analysis) of the Act. A result below the threshold is disregarded.

Ketamine is not yet on the list. Parliament did approve the addition of ketamine in May 2026. According to the parliamentary preparatory documents, however, that addition will only enter into force on a date set by the King, once saliva tests capable of detecting ketamine are available. The official consolidated text of the Act as of November 2026 does not yet mention ketamine.

Which medication can produce a positive saliva test?

Article 37bis makes no distinction between an illegal drug and a medicine. If your medication contains a listed substance, or if your body converts it into such a substance, a test may come back positive.

• Morphine. Painkillers based on morphine directly contain a listed substance.
• Codeine. Codeine is found in some painkillers and cough medicines. According to the official product information, codeine is converted into morphine in the liver, so a positive result for morphine is possible in that case too.
• Cannabis-based medicines. A cannabis-based medicine containing THC may produce a positive result for THC.
• Certain ADHD medication. Some ADHD medicines belong to the amphetamine group. A positive result for amphetamine cannot then be ruled out. Ask your doctor or pharmacist what this means for your treatment.

Other medicines are not on the list as substances, such as methadone, tramadol, sleeping pills and sedatives. Article 37bis does not apply to them. They can, however, seriously impair your ability to drive, in which case Article 35 may come into play. For more on how the test works, see our article on a positive saliva test at a drugs check.

When is the use of medication a criminal offence?

There are three situations in which medicines can lead to prosecution.

• A listed substance above the threshold. If the saliva or blood analysis shows an Article 37bis substance at a concentration equal to or above the threshold, the offence is in principle established, even if the substance comes from a medicine.
• A state resembling drunkenness. If you drive with visible signs of impairment, such as drowsiness, slow reactions or an unsteady gait, Article 35 may be applied, whichever medicine causes it.
• Unfit to drive. The Highway Code requires you to be physically fit and to keep your vehicle under control at all times. Anyone unable to do so because of medication also breaches that rule.

Refusing a saliva test, saliva analysis or blood test without a legitimate reason is also an offence under Article 37bis. If you put forward a legitimate reason, for example a medical one, a doctor assesses that reason.

What penalties do you face?

For offences committed on or after 1 September 2026, the new Criminal Code applies with its penalty levels (strafniveaus / niveaux de peine). Penalty level 1 means that the judge chooses between, among other things, a fine, community service of 20 to 120 hours or a probation sentence of 6 to 12 months, but no prison sentence. The amounts below are the amounts actually payable.

In addition, after a positive saliva test or a refusal, the police impose a temporary driving ban of 12 hours (Art. 61ter). That ban may also be imposed where the test is negative but you are clearly in the state referred to in Article 35. Before you may drive again, a new test is carried out.

For offences committed before 1 September 2026, the old penalty system continues to apply, unless the new law is more lenient (Art. 2 Criminal Code). See also our article on the new Criminal Code and road traffic and on the driving ban (verval van het recht tot sturen).

Is a medical prescription a defence?

Article 37bis contains no exception for prescription medicines. A prescription therefore does not automatically rule out prosecution where the analysis shows a listed substance above the threshold. For Article 35, too, all that counts is how you were actually driving.

In practice, however, the prescription is an important document in your file. It shows where the measured substance came from and that you followed your doctor’s dosage. Whether this can lead to an acquittal in your specific case is not expressly regulated by law and depends on the circumstances. In any event, it carries weight in the judge’s assessment, including the choice of penalty.

A favourable measure such as a suspended verdict (opschorting / suspension du prononcé) or a suspended sentence (uitstel / sursis) may then be discussed. Read more in our article on suspended sentences and suspended verdicts.

The role of your doctor and the package leaflet

The driving licence rules place a clear duty on the doctor. Under Annex 6 to the Royal Decree of 23 March 1998, the doctor checks what effect a medicine has on driving behaviour, alone or in combination with other substances or alcohol, and informs the patient of the possible consequences. According to the same annex, anyone who regularly uses psychotropic substances that endanger fitness to drive is not fit to drive.

The package leaflet contains a section on driving and using machines. Be sure to read it at the start of a treatment or when the dose changes. Vias has been calling for years for a system of pictograms on the packaging, following the French example. Until that exists, the leaflet, your doctor and your pharmacist remain your main sources of information.

The risk is real. According to Vias, 3 to 4% of road accidents in Belgium are attributable to medicines, and combining sleeping pills or sedatives with alcohol sharply increases the risk of an accident.

What should you do?

1. Do not refuse the test. Refusing without a legitimate reason is itself an offence, carrying the same penalty range as a positive result.
2. Mention your medication. State which prescription medicines you take and have this recorded in the police report (proces-verbaal).
3. Keep your evidence. Keep the prescription, a certificate from your doctor, your medication schedule and the packaging.
4. Consider a second analysis. You may have a second saliva analysis carried out at your own expense by an accredited laboratory (Art. 62ter). Discuss with us promptly whether this makes sense in your case.
5. Respect the driving ban. Do not drive during the temporary 12-hour ban. Driving during such a ban is a separate offence.
6. Respond to a summons. Read what to do in our article on a summons to the police court (dagvaarding) and have your case prepared in good time.

How Novex Advocaten can help

Our firm assists drivers before the police court (politierechtbank / tribunal de police) every day, including where a medicine is the cause of a positive test. We check whether the procedure was followed correctly, whether the measured value exceeded the threshold and whether the substance is explained by your treatment.

More information can be found on our page on drugs and driving and on our general road traffic law page. We plead before the police courts in Dutch or French. You can contact us in Dutch, French, English or Arabic.

We agree on our fees clearly and in advance. Legal expenses insurance often covers the costs; read our article on legal expenses insurance.