Impaired By Drug

This information is not a replacement for getting a lawyer.

Do not take this article as personal legal advice, because it’s not. Every legal situation is different, and this article is only intended for general information and educational purposes.

One of the very few situations in which you are compelled by law to cooperate with the police is when you are being investigated for driving while impaired by drug. There are three sets of tests which you may be required to perform. These three tests are described below

1. On the roadside – Standardized Field Sobriety Test

The police officer on scene may, in order to determine if he has reasonable grounds, demand that you perform the Standardized Field Sobriety Test (“SFST”). Failure to take the test is a criminal offence. The SFST test has three components (the nystagmus test, the “walk-turn” test and the “one leg stand” test). The results of these tests are not admissible as evidence that are you impaired, rather they provide the officer with the reasonable grounds to take you to the station to be evaluated by a Drug Recognition Expert (“DRE”) officer.


2. At the station – Evaluation by DRE officer

If a police officer believes on reasonable grounds that you have been operating a motor vehicle while impaired by drug then you may be required to attend at the police station for a drug evaluation by a DRE officer. If the police make a demand that you participate in an evaluation by a DRE officer then you have to participate or you will be charged with what is called “refuse to comply.

The evaluation will involve the DRE officer doing the following:

  • taking your pulse;
  • examining your eyes for nystagmus, which is an inability of the eyes to maintain a visual fixation as the eyes move to the side. This test is not applicable to cannabis users; and
  • conducting the following divided attention tests:
    • Romberg balance test: you must stand with your hands at your sides and close your eyes. The test lasts for 30 seconds. Note that the DRE officer will not tell you it will be 30 seconds;
    • walk and turn test: you must walk toe to heel with your toes and heels not more than ½ an inch apart in a straight line;
    • one leg stand test: you must stand on one leg for 30 seconds with your arms held at the side of your body;
    • touch finger to nose test;
  • check vital signs and again check pulse;
  • check pupils, nasal cavity and ingestion exam (for cannabis the DRE will conduct a non-convergence test to determine if you can cross your eyes); check muscle tone;
  • check for injection sites and take 3rd pulse;
  • interrogate. Note that you are not obliged to respond to the interrogation; however, there are certain questions that you must answer. They are:
      • whether you need sleep;
      • whether you have eaten that day;
      • whether you are epileptic; and
      • whether you are under the care of a doctor or dentist.

If you do answer any questions because you think you have to then you should indicate that you are answering the question because you think you are legally required to do so. You will find attached a chart used by DRE officers. The chart indicates what drugs supposedly cause what effects on the body.

DRE chart

3. Toxicology Testing

If you fail the evaluation, then you will be charged and you will be required to provide a urine or blood sample which will be sent to Health Canada for toxicology tests. The urine test indicates only if cannabis (or any other drug) is in your system. It does not indicate how much of that drug was in your system at the time or whether that drug was impairing your ability to drive. The DRE officers will concede that cannabis remains in the body for at least 30 days which means the toxicology tests do not tell the court much. Often, a urine test will only show the presence of Carboxy-THC, the inactive metabolite of marijuana, which will make proving any impairment much more difficult for the Crown. If they proceed with a blood test then there is a higher chance that THC will be found. A toxicologist can determine the concentration of that THC and be called to testify as to how your level of THC would affect a normal person. If you are given the option you should provide the urine sample.

It should be noted that in both urine and blood they can find either THC or carboxy-THC. THC is the active drug and carboxy-THC is the inactive metabolite. Urine tends to show carboxy-THC and not straight THC, and this is why urine samples are better for defendants, because impairment is only caused by THC and not by carboxy-THC. Thus if they cannot show THC, a toxicologist cannot state whether there was an impairing quantity.

So, if they do find THC, then an expert still has to determine if there is enough THC to cause impairment, and then they must try to relate average abilities to handle that amount of THC to the ability of the specific person to handle that amount of THC.



Nathan Baker
Law Office of Richard J. Aitken
P.O Box 2126
263 Charlotte Street
Peterborough, ON K9J 7Y4
Tel. # (705) 742-0440
Fax # (705) 742-0889

NORML Canada