Many questions need examining to establish effects of legalized cannabis on work safety

Co-authors of pending systematic review on central nervous system agents outline what we know — and don’t — about OHS implications of legalized cannabis

The Canadian federal government has committed to making recreational marijuana legal by July 1, 2018. As that date approaches, many workplaces are concerned about the implications this change may have for occupational health and safety (OHS).

At the Institute for Work & Health (IWH), Scientist Dr. Andrea Furlan and Post-Doctoral Fellow Dr. Nancy Carnide have been examining the research literature to learn more about potential implications. Their search of the literature is the first step in a systematic review they are conducting on the effects of various central nervous system agents, including marijuana, on workplace injuries, deaths and near misses.

Although the systematic review is still underway—and findings are not yet available—Furlan and Carnide have agreed to share what they know from the literature in a Q&A with At Work.

Q: Recreational marijuana has become legal in some U.S. jurisdictions in recent years: Colorado, Alaska, D.C., Oregon and Washington. What research has been done on whether marijuana use increases in the workplace following such legalization?

A: As far as we are aware, no published studies to date have examined the impact of recreational marijuana legalization on the workplace. The only data we have seen is from a report released this year by a large private drug-testing company in the U.S. It found that the rates of positive cannabis tests in Washington and Colorado in 2016 outpaced the national average for the first time since the two states legalized cannabis in 2012. But these rates were based on the number of tests conducted. Also, they do not necessarily reflect increased use or impairment in the workplace.

Q: What research has been done on the impact of marijuana use on workplace health and safety?

A: Several studies have examined the impact of marijuana use on a number of workplace outcomes, but with mixed results. Some have found associations between marijuana use in the workforce and work absenteeism, reduced productivity, job turnover, disciplinary measures, workplace accidents and injuries, unemployment and interpersonal conflict. However, other studies have found no association with some of these outcomes. Overall, the evidence to date is quite inconsistent.

Earlier this year, the National Academies Press, a publishing body of the National Academy of Sciences in the U.S., published a major report on the health effects of marijuana use. One of the areas they examined was the effect of marijuana on injuries and accidents, including injuries and fatalities in the workplace setting. Based on six main studies, this review did not find enough evidence to either support or refute a statistical link between marijuana use and occupational injuries or accidents.

Q: Have there been any studies on marijuana use and safety-sensitive jobs?

A: There are very few studies on marijuana and safety-sensitive situations at work. Most of the studies are about driving, which are then extrapolated to work settings. And even in driving, the research is in its infancy. There’s not a lot of consensus. Researchers know marijuana use impairs driving, but they don’t know much about how it impairs driving. What is consistent in the few studies out there is that reaction time is slower, so people also drive slower.

Also, it’s not clear to what extent you can extrapolate driving to work situations. Driving is a learned activity that many people do almost on auto-pilot. Drivers’ brains are often multi-tasking; many people are talking or doing a secondary task while behind the wheel. That kind of activity may be similar to some work situations, but not to others.

What you’ll find more in workplace settings are post-accident investigations where the people involved are tested to see if they were under the influence of marijuana or other drugs. These are done on a case-by-case basis, and the problem with relying on these investigations is that the accidents may have happened even if the workers had not been under the influence.

These kinds of cases tend to be more publicized, but you need rigorous research with control groups to determine whether the frequency of accidents is actually higher among those using these drugs than among those who are not. And just because people test positive for tetrahydrocannabinol (THC) in their urine does not necessarily mean that they’re impaired. That’s the other problem that we have.

Q: Can you explain why it’s so difficult to develop a test of impairment?

A: Part of the problem is that marijuana remains in the system for quite some time beyond the actual time of impairment. So someone can use marijuana on Friday night and come into work on Monday no longer impaired, yet test positive for marijuana use. There is no consensus as of yet on the levels of THC detected in fluids that indicate acute impairment.

The question of impairment also depends on how marijuana is ingested. Nowadays, people can use marijuana in many different ways. They can smoke it or vape it—in other words, ingest it via the lungs. Or they can ingest it via the digestive system, by swallowing edible cannabis oil in capsules or eating brownies with the oil baked in, for example. The effects of edible cannabis are slower to kick in and last longer than the effects of cannabis that has been inhaled. But we don’t even know the degree of impairment when people ingest edibles, never mind how long the impairment lasts.

Keep in mind that, in the world of alcohol research, where they’ve now established the blood-alcohol content considered too impaired to drive, people started doing research 50 years ago. To even develop a roadside test for marijuana akin to a roadside test for alcohol, you would need to know what areas of the brain are affected by marijuana. They might not be the same parts of the brain that are impaired under the influence of alcohol, or opioids, or benzodiazepine (sleeping pills).

Q: From a workplace health and safety perspective, what differences are there between medical marijuana use and recreational marijuana use?

A: Marijuana is made up of over 70 cannabinoids. THC and cannabidiol (CBD) are the main ones researched. THC is the cannabinoid responsible for the impairing, psychoactive effects—the “high” felt after consuming marijuana – while CBD produces no psychoactive effects. Typically, recreational users of marijuana will seek euphoria and opt for marijuana containing a higher THC percentage. Medical users are generally using marijuana for therapeutic purposes and may be less inclined to consume to get high. Having said that, the THC concentration in medical cannabis in Canada can vary anywhere from one per cent up to 25 per cent, and it is up to individual patients to decide which strain and concentration works best for their condition. 

Another difference is that people who use cannabis for medical purposes may need to use it every day, and many times during the day. As a result, they may develop a tolerance to the effects on their attention, concentration, reaction and so on. On the other hand, people who use marijuana for medical purposes may over time develop a liking for the euphoric effects of marijuana. It’s not always easy to distinguish usage patterns between people who use cannabis for medical purposes and those who use it for recreational purposes. Any difference in workplace safety risks between recreational and medical users hasn’t been studied as far as we know.

Q: You’ve been reviewing and assessing the quality of existing studies on this topic for a systematic review. What questions have researchers been able to answer, and what are they tackling next on this topic?

A: As mentioned earlier, several studies have examined the relationship between cannabis use and various workplace outcomes, with inconsistent results.

Some of the inconsistency in the findings may be due to differences in study methodologies and difficulties in conducting this type of research. Some study designs preclude the ability to assess cause and effect in the relationship. Another common design limitation is the lack of a control group. Other issues include insufficient sample size of cannabis users, failure to account for confounding factors (other factors that may influence outcomes), and a lack of consideration of the timing of use and impairment in relation to outcomes such as accidents and injuries.

While a great deal of concern exists in the workplace community around the effects of cannabis, particularly with the impending legalization, we need high-quality observational studies to be able to better answer questions about its effects on work, including its effects on health and safety.

At a more basic level, we have limited data on the extent of cannabis use and impairment among workers, and this is true in both the U.S. and Canada. The best estimates we have in Canada reflect overall use, which includes use away from work and, therefore, may be of limited relevance to OHS. We know virtually nothing about the current magnitude of workplace cannabis use —i.e. use during work, on breaks and in the hours prior to beginning a work shift.

Also, an important area of occupational health research not often considered in the context of legalization is the potential health impact on workers involved in the production of cannabis. Some researchers in Washington State are beginning to look at this, with an initial focus on the effects of UV radiation.

Finally, one of the key avenues for future research will be to identify an accurate measure of impairment for use in workplaces. This is something that the workplace community is particularly keen to see.

Furlan and Carnide expect to finish their systematic review in the summer of 2018. Watch for their findings in an upcoming issue of At Work.

Source:  At Work, Issue 90, Fall 2017: Institute for Work & Health, Toronto