Driving Under the Influence of Drugs
It is a common misconception that a “DUI” only relates to impairment by alcohol. This is inaccurate. CC 253(1)(a) relates to impairment by “alcohol,” a “drug” or any combination thereof.
This makes litigation in this area highly complex. The effects of various illegal and legal narcotics is generally not as well understood as alcohol. For example, while most members of the bar, bench and police have some experience with alcohol, this is not true of illegal and legal narcotics. Indeed, unlike alcohol, in most cases it is not true of the general public.
Proof of actual drug impairment is currently based heavily on “specialist” police officers. Such officers typically have no significant scientific background at all. Essentially, the partisan police officer sits in the place of both the approved instrument and the approved screening devices used in an “impaired by alcohol” prosecution. This is problematic, as it moves a great deal of the analysis to a comparatively subjective person.
For example, although one can dispute the readings of the approved instrument for alcohol, at its core they are based on real science. Generally, approved instruments make a prediction of blood alcohol level based on a sample of the accused’s breath. The prediction is based on “Henry’s Law,” which generally states that, in a closed environment the amount of alcohol in the air above a sample of alcohol can be used to predict the alcohol content of the sample, assuming a given partition ratio. While thoughtful people may well disagree as to the empirical validity of this metric, there is no doubt that it is broadly based on solid science. Moreover, by being based on real science, it has the benefit of being challenged by the scientific method when changes develop in technology or research methods.
Contrast this with the current “impaired by drugs” system, which, as a practical matter, relies almost exclusively on the police officer.
Impaired By Drugs Under the Criminal Code
The “drug demand” sections of the Criminal Code are analogous to those for alcohol.
CC 254(3.1) states that where a peace officer has reasonable grounds to believe that a person is committing, or has committed within the last three hours, the offence of impaired operation by the consumption of a drug or the combination of alcohol and a drug they can make a demand for an evaluation conducted by an evaluating officer to determine whether the person’s ability to operate a motor vehicle is impaired.
CC 254(3.3) states that this drug evaluation procedure must be carried out by an evaluating officer and can include a breath test on an approved instrument if the evaluating officer has a reasonable suspicion that the person has alcohol in their body.
CC 254(3.4) states that if, after completing the evaluation, the evaluating officer believes on reasonable and probable grounds that the person’s ability to operate a motor vehicle is impaired by a drug or by a combination of alcohol and a drug, the evaluating officer may make a demand for a sample of oral fluid, urine or blood.
There are several tests that are authorized via CC 254(3.1). They are:
- measuring the accused’s pulse, determining if the pupils are the same size and that the eyes track an object equally
- eye examinations such as the horizontal gaze nystagmus test, the vertical gaze nystagmus test, and the lack-of-convergence test
- divided-attention tests such as the Romberg balance test, the walk-and-turn test, the one-leg stand test and the finger-to-nose test,
- examining the accused’s blood pressure, temperature and pulse
- examining the size of the accused’s pupils, and nasal and oral cavities
- examining the accused’s muscle tone
- examining the accused’s arms, neck and legs for evidence of injection sites
The term “Physical Coordination Test” is more common in Canada. It can be thought of as synonymous with “Standard Field Sobriety Test,” or “SFST,” which was developed in the United States.
Unlike the relatively subjective assessment of an individual officer, actual impairment by a drug (or lack thereof) is based on the science of pharmacology. Pharmacology is the is the study of drug action on the body through chemical processes. Essentially, it involves the analysis of the interactions between the substance and the body. The achieve an effect, the substance binds with a part of the body, which then causes a chemical process.
This interaction can be broken down into two interconnected concepts: pharmacodynamics and pharmacokinetics. Pharmacodynamics is the drug’s effect on the body, whereas pharmacokinetics is the effect that the body has on the drug. Pharmacodynamics, broadly speaking, is the primary mechanism of action of that specific drug. Pharmacokinetics, on the other hand, includes things like the processes of absorption, distribution, metabolism and elimination/excretion.
When a drug is consumed, it begins to be administered into the body. For example, drugs that are taken orally typically pass through the liver fist, which alters the drug’s bioavailability to the rest of the body. This means that the amount of the unchanged drug is typically less by the time that it reaches the circulation blood. The drug is then distributed to various sites throughout the body. In most, but not all, cases, the drug will bind to a specific receptor in a “lock-and-key” fashion on the cell surface in a specific part of the body. The binding of the drug to a receptor changes the shape of the receptor, which can activate molecules bound to the receptor on the inside of the cell.
Driving Under the Influence of Marijuana
The active drug in marijuana is Delta 9-tetrahydocannabinol, or THC. The effect of THC in a given instance depends largely on the potency of the plant used and the route of administration.
Almost immediately after smoking, there is a rapid increase, and then rapid decrease in THC plasma levels. The THC is metabolized to the psychotropic active 11-OH-THC metabolite and then further oxidized to THC-Acid, which appears in both drugs and urine. This is the metabolite that is usually tested for in urine drug screens.
Smoking of marijuana produces very low blood levels of the (active) 11-OH-THC metabolite which is being converted to the (inactive) water-soluble THC-Acid. This is what eventually appears in both blood and urine. Thus, when urine drug screens for prior marijuana use are done, it is the inactive THC-Acid that is tested for, not the THC itself.
On the other hand, when marijuana is eaten (for example, in brownies, etc) it is absorbed through the gastrointestinal tract and eventually returns to the liver where is it also converted to 11-OH-THC. The process converts far greater amounts of 11-OH-THC that when smoked.
Unlike alcohol, there is little correlation between the tested THC and actual impairment. For example, when a tested BAC is (say) 200 mg/% in a given subject, then that subject is almost certainly “more” impaired than when their BAC is at 100 mg/%. Moreover, after the expulsion of alcohol from the accused’s blood, it is safe to say that they are no longer impaired at all (potential hangovers, notwithstanding). The same cannot be said for marijuana, which makes the prosecution of these offences highly challenging for the crown.
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