Measuring THC Blood or Urine Content Will Not Detect Impairment

The Canadian and BC governments are facing some difficult legal hurdles if they continue to pursue the notion of punishing people on the basis of having consumed particular qualities of marijuana before driving. 

​Earlier this month, I wrote about how the BC government will be introducing a 90-day Administrative Driving Prohibition for marijuana impaired driving and the flawed options available to how they will determine if someone is driving while impaired. 

And I’ve previously been quoted in articles about how significant an effect these poorly conceived laws will have on medical users. 

But what does it look like when Criminal courts, which require proof beyond a reasonable doubt, try to handle cases involving marijuana impairment? 

Urine and blood tests can prove a person consumed marijuana. That much is agreed upon and established in the courts. But that’s it.

It can only prove that the person used marijuana in the past. What urine and blood tests cannot do is prove whether a person was impaired as a result of marijuana use.

Can THC content in the urine or blood prove impairment? 

The likelihood that the Government will be able to draw a rational connection between a urine or blood THC content and impairment by a drug is seriously undermined by a recent decision of our courts. This case is a good forecast for how courts will likely view the evidence of marijuana impairment led by way of THC content in blood or urine. 

This year, the BC Supreme Court ruled on a case of Kevin Miller, who was accused of breaking a supervision order prohibiting him from using intoxicants. Miller was supervised at Belkin House and the Chilliwack Community Corrections Centre (CCCC), and had been on the order since 2010. In 2014, he wanted to use medicinal marijuana to deal with his arthritis, sleeping problems, and generalized anxiety. The major issue at the centre of the case is whether he breached his supervision order by smoking medical marijuana, which could be considered an intoxicant under the  Corrections and Conditional Release Act. This case demonstrates how prosecuting someone for impairment by marijuana becomes challenging. 

Miller asked his supervising officer at Belkin House about getting a prescription for medicinal marijuana. The officer told him he would have to get a prescription and have it filled at a legally-licenced producer. Miller returned with a prescription from a doctor and mentioned that he purchased and smoked some marijuana, however, the officer’s superior noted that it was missing details such as how much marijuana should be taken. This could raise concerns that he was taking the drug recreationally, breaching his supervision order. But how do you draw the line between a proper, medicinal use and an impairing, recreational one? Either way, things at this point seemed to be going well for Miller, as far as getting a marijuana prescription goes.

But eventually, Miller’s supervising officer changed in 2016 when he went to the CCCC. Miller’s new officer told him he would have to have a prescription and that Correction Services Canada would not let him store marijuana in their facilities. The new officer told Miller the process of getting a prescription was very complex and involved a lot of paperwork. Miller contested this, arguing that he had acquired a prescription and that it was on file. 

His new officer did not have the prescription on file and referred Miller to a nurse. Miller tried to get a new prescription, but could not get to Abbotsford where he originally had gotten his prescription because it was a significant distance from Chilliwack. Frustrated by his new officer’s denial that he had obtained a prescription, he asked the dispensary he used before to transfer his prescription to one in Chilliwack. He asked the new dispensary if they could hold onto any marijuana he purchased so as to not violate the CCCC’s rules and he bought and smoked a small quantity aware that it would show up on his urinalysis. He expected he would be able to talk about the results and verify that he had gone through the proper channels to smoke medical marijuana and was not using it to get intoxicated. Instead, he was arrested for violating his supervision order. 

This set the table for a very challenging case. Crown had to prove that in Miller’s example, marijuana was being used as an intoxicant, that Miller intended to breach his condition, and that if marijuana was being used as an intoxicant and Miller intended to use it as an intoxicant, that Miller did not have a reasonable excuse for doing so. 

Miller was very careful with his strain selection, choosing marijuana he knew had a lower tetrahydrocannabinol carboxylic acid (THC) percentage and a higher cannabidiol (CBD) percentage. This meant the marijuana would be more effective at relieving pain, mood problems, and appetite. In comparison to high THC marijuana, which might be preferred among recreational users.

Miller’s urine sample showed he had 63 nanograms of THC per millilitre on September 24, 2016. He was not tested for how much CBD he had in his system, which blocks the euphoric effects of THC. Even the Crown’s expert witness, a toxicologist and pharmacist, noted CBD has anti-intoxicant effects. 

This is one of the things that are very important about this case: the court was unclear about whether or not the impairing effects of marijuana were actively present and how they can be judged. The Crown’s witness was clear, as well as many scientists, that the effects of marijuana, unlike alcohol, vary widely from person to person. While Miller undoubtedly consumed marijuana, it could be argued quite reasonably that he was not using the drug as an intoxicant. 

Defence counsel submitted that the definition of an “intoxicant” under the Corrections and Conditional Release Act is: 

Intoxicant means a substance that, if taken into the body, has the potential to impair or alter judgment, behaviour or the capacity to recognize reality or meet the ordinary demands of life, but does not include caffeine, nicotine or any authorized medication used in accordance with directions given by a staff member or a registered health care professional.”

By that definition, Miller was okay to use a medically-authorized substance and still conform to the rules set out that prohibited him from consuming intoxicants. 

The judge ultimately agreed that Miller did, beyond a reasonable doubt, consume what could be considered an intoxicant. However, the judge was left with a reasonable doubt that he intended to breach the condition of his prohibition on using intoxicants. Miller was found not guilty but was warned that he would have to speak to his parole officers to get proper authorization to use marijuana in the future. Here’s what the judge said:

Mr. Miller wanted to use marihuana for medical purposes and to do so legally. I accept he honestly believed a suitable strain would treat certain medical conditions afflicting him. He was advised the first step was to get a prescription from a doctor. He obtained what I accept he believed to be a proper prescription from a doctor. There is no evidence he was aware of or made aware of formal shortcomings in the prescription that according to the regulations governing the prescribing and dispensing of medical marihuana negative its being a prescription. He testified he was interested only in the medicinal element of the marihuana, not THC, not interested in any intoxicant effect.”

This case is a perfect foil for what will happen if and when the Government tries to regulate driving by the imposition of THC blood content limits. The science will not support that this is a reasonable prohibition. The science already does not support that a person is impaired based on having any particular blood or urine THC content. Enacting bad laws that are not supported by science will be met with this type of treatment from the Courts. The Government should heed this case as a caution of what is to come. 

Since we know different strains of marijuana have different effects, and those effects vary from person to person based on numerous factors, it is impossible to know whether or not someone is really impaired when they’ve used marijuana.

This case also adds an interesting layer of addressing how will the government deal with CBD as a possible mitigator of the impairing effects of THC? There is no provision to test for CBD under any of the currently proposed legislation. 

It is clear from the legislation that is currently being reviewed that the government has not put enough thought into how the impairing effects of marijuana can be mitigated through using marijuana in a smart way. Cases like Mr. Miller’s present a clear problem for Crown in trying to prove someone was impaired by marijuana. If the government tries to enforce a strict definition of what is impairment by marijuana, it will likely be subject to the same treatment by the courts.

15 thoughts on “Measuring THC Blood or Urine Content Will Not Detect Impairment”

  1. what about the studies….government says it has studies that prove smoking impairs….while we here of other studies that there is no impairment and often the opposite, smoking often impoves driving skills?
    should we not demand full disclosure of these studies and cross examin them?

  2. Functionality tests far exceed the capabilities of a drug/alcohol test. Sleep impairment is a major difficulty on our roadways. Anxiety messes with functionality however, so a relaxed enough process to give people their bearings before testing, or even allowing retesting, would make a mountain of difference.
    I also think insurance companies could offer premiums to people willing to implement a breathalyzer in their ignition.
    Changes in road laws, functionality tests, and insurance mandated breathalyzers would bring us to a place where road side pirates stop looking like a mascot for our police forces which give them a very bad rep.

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