Imperfect Science of Cannabis Impairment Testing

Imperfect Science of Cannabis Impairment Testing

WIS has highlighted key points in this article.
(Feb. 14 / 2019)
Employers face a serious challenge in cannabis testing in the workplace — the current science cannot test for present impairment. Cannabis has unique qualities that make it unlike other drugs or alcohol. It is processed differently by the body, creates inactive byproducts and is retained in body tissue for weeks or longer.

This does not mean employers are without tools to test for cannabis impairment on the job. But their approach needs to be tailored and combine science and physical observations in a way that best fits their business.

So why is cannabis impairment so hard to test for? And what methods can be combined by employers?

THC, metabolites and variability
Tetrahydrocannabinol (THC) is the psychoactive, impairment-causing component in cannabis. The human body metabolizes THC into a psychoactive compound, which is then metabolized further into a non-psychoactive one. There are 18 different metabolites of cannabis identified in the urine, the primary one (carboxy-THC) causes no motor or mental effects.

Cannabis is a fat-soluble drug and THC is stored in the body’s fatty tissue even as blood levels fall quickly. Fat-soluble drugs can be detected through testing for a significant time after use.
Individual variables also come into play in testing, such as a person’s duration of use, time between use, metabolism, body size, frequency of ingestion and THC content in the product used. These factors can drastically increase the lingering impairment effects of cannabis.

Methods of testing
Urinalysis: Urinalysis does not test for the active components of cannabis, but for the inactive metabolites (a byproduct of THC). The presence of these metabolites only establishes prior use, not present impairment. To put it another way, urinalysis testing for cannabis impairment is testing for byproducts in a byproduct.

Inactive metabolites can continue to be found in urine well after the psychoactive, acute elements of the drug have disappeared from the employee’s system. This means an employee can test positive for cannabis use on a urine test and not be under its influence or impaired by it at all.

Oral fluid: Oral fluid testing has a distinct advantage over urinalysis. It tests for the impairing THC compound, not the metabolites that occur once the body has processed the drug. The presence of THC in oral fluid can be generally regarded as evidence of recent cannabis use. Oral fluid testing is the scientific method police are using in roadside tests for impaired driving in Canada.
Yet the challenge of testing for present impairment remains. Since people have different absorption rates and metabolisms, the presence of THC still does not necessarily mean impairment; it means that an individual has used cannabis recently.
Blood: The presence of THC can be accurately and effectively found in the blood. Questions remain, however, whether this constitutes impairment. Blood testing aims to solely measure THC content but can it can give mixed results by including metabolite byproducts, depending on the extent of usage.

Courts have said that blood tests are preferable to urinalysis and even to oral fluid testing. But courts still do not suggest a high degree of reliance on blood testing as an incontrovertible tool to indicate that relatively small levels of THC in the blood can lead to a finding of impairment.

Physical indications: Some physical signs of severe impairment seem easy to discern. These include confused thinking, slurred speech, dilated pupils and the observation of the smell of cannabis. Employers, however, must be cautious in using non‑regulated measures of impairment. The law has shown they do not have the ability to determine impairment on an ad hoc basis.

Employers may need to rely on a combination of drug testing and physical observations. Arbitrators have accepted evidence that individuals can be trained to observe signs of impairment. It does however require time, expertise and training to become proficient at psychophysical testing.

The Canadian Model — Alcohol and Drug Guidelines is a valuable resource for employers. This “best‑practice” tool was developed for those in the construction industry but has spent the time and money to collaborate with medical professionals and industry leaders to establish standards for drug and alcohol testing.

Looking ahead

A completely new landscape of drug testing in the workplace emerged in Canada with the legalization of recreational cannabis on Oct. 17, 2018. It will change again when cannabis edibles, beverages, extracts and topicals are permitted for sale in October 2019 or later.
Supervisors should be trained to identify behavioural anomalies that indicate impairment from cannabis on the job. However, it is important to remember that such behavioural indicators may be caused by fatigue or stress. Having an employee assistance program in place provides employees with the opportunity to reveal any drug dependency problem they may have. Appropriate drug testing can properly be part of an employee’s rehabilitation program.
In addition, work policies should require that employees disclose any drug use, including cannabis, that might impair the performance of their job — even in non-safety sensitive positions. The drug testing regimen, notwithstanding the present impairment limitations, should be part of this broad approach.