The Science Behind Marijuana Testing at Work

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The human brain has a unique ability to take in information, block out unnecessary data, analyze it and issue a motor response—all within fractions of a second. It is one of the many reasons why humans are at the top of the food chain.

But the ability to process information, make a quick decision and act accordingly can be affected when under the influence of marijuana. All the steps involved in decision making slow down, which can—in some cases—cause catastrophic, unintended effects.

For instance, after smoking a joint with friends, a young man got behind the wheel of his car. He was aware that he was under the influence, so he adjusted his driving accordingly by driving slower than he normally would, explains Marilyn A. Huestis, Ph.D., member of the World Anti-Doping Agency's Prohibited List Committee and former senior investigator and chief of the Chemistry and Drug Metabolism Section, IRP, at the National Institute on Drug Abuse at the U.S. National Institutes of Health.

Up ahead in the road, an old man began walking across the street. The driver saw the pedestrian and mentally calculated that he was traveling slow enough that the man would be across the street by the time the car arrived at his location.

But, a few seconds later, the old man dropped a set of keys in the road. He bent over to pick them up, slowing his pace across the road. The driver saw the man stopped in the road, but his reaction speed was too slow, and the car continued moving forward—hitting the older man.

The incident was tragic. But just because marijuana affected this particular young man in this way does not mean that it would have the same effect on another user, Huestis adds.

"You can't come up with a single [limit] that is going to differentiate between unimpaired and impaired," she explains.

Marijuana is the most commonly used Schedule I drug in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC), with approximately 37.6 million users per year. A wide range of U.S. states have legalized marijuana for medicinal or recreational use, despite its continuing illegality at the federal level. Uruguay and Canada have also legalized the recreational use of marijuana.

Quest Diagnostics, which conducts drug testing for employers, reported in 2019 that many employers are dropping marijuana from their preemployment screening drug tests. But employers who do continue to test for marijuana have seen an increase in the number of employees and potential employees testing positive for the drug, says Dr. Barry Sample, director of science and technology for employer solutions at Quest Diagnostics.

"For the general workforce test, if we look at the positivity rates in recreational use states and medical use states, there's very little difference in positivity," he explains. "Where you see the difference, really and not surprisingly, is in the recreational use states and the nonrecreational use states."

Sample adds that tests only show whether someone has used marijuana—not if that individual is under the influence.

"What you need to remember is it doesn't matter if it's urine, oral fluid or hair testing—it just reflects use," he says. "It doesn't inform you whether someone was impaired or what their usage patterns are."

The amount of tetrahydrocannabinol (THC) in marijuana determines its strength, and it can have vastly different effects on users depending on their body weight, method of consumption (smoking versus edibles) and patterns of use—occasional users compared to daily users, for instance.

Researchers are still learning about how marijuana affects the body, but they do know that it directly impacts the brain and the parts responsible for memory, learning, attention, decision making, coordination, emotions and reaction time, according to the CDC.

"Heavy users of marijuana can have short-term problems with attention, memory and learning, which can affect relationships and mood," the CDC explains. "Marijuana also affects brain development. When marijuana users begin using as teenagers, the drug may reduce attention, memory and learning functions and affect how the brain builds connections between the areas necessary for these functions."

However, some research into marijuana usage indicates potentially beneficial side effects. For instance, cancer patients may find medical cannabis helpful in treating the nausea and vomiting caused by chemotherapy treatments. The drug has also been shown to be helpful in treating neuropathic pain—pain caused by damaged nerves.

But broader research and understanding of how marijuana impacts the human body has been difficult to conduct in the United States due to the drug's Schedule I classification. This has also prevented researchers from determining, as with alcohol, at what point a person is considered impaired after using marijuana.

"It's really a decision—an administrative decision—that balances the risk of people driving impaired versus society's tolerance for higher levels of impairment," Huestis says.

In the United States, after decades of research, the nation decided to set impairment for alcohol at a rate of 0.08 blood alcohol concentration level. But this is much higher than the rest of the world, which trends at the 0.05 level.

"When you think about drawing a line in the sand, you could have an alcoholic who drinks huge amounts who is less impaired, versus an occasional user who is more impaired at 0.08," she adds.

When it comes to marijuana and measuring THC, Huestis says it's even more difficult. After Canada legalized recreational use of marijuana, Huestis explains that the government began exploring creating an impairment cutoff, but so far it has not established one.

Huestis has been studying the effects of marijuana since the 1980s, and during the first five years of her career she was able to conduct research only on occasional users—such as individuals who smoke marijuana once every few weeks.

So, she and other researchers created a study for their work with the National Institute of Drug Abuse in Baltimore. They established a residential unit where frequent marijuana users—those who used multiple times per day—could be brought in to test how long the drug remains in a person's system.

"Because they were volunteers, they could leave whenever they wanted to, but they could not come back and participate in the study later on," Huestis says.

The volunteers would enter the facility in the evening around 9 p.m and were not allowed to bring any drugs with them. The research team would then conduct tests on the volunteers in the morning to create a baseline data set from blood, urine, oral fluid and brain imaging.

"What we found was astounding, and it really caused us to look at all of the regulations around driving under the influence, how people tested positive and what we knew," Huestis explains.

The research team wrote three major papers based on its findings in Baltimore, including one about THC levels in blood samples. The research team looked at blood sample results taken the morning after the frequent users had checked into the research facility.

"These individuals reported that they used at least daily, multiple times per day, and half of their samples were negative—it was 19 hours between when they came in and we took the sample," Huestis says. "We also found that in other users we could measure THC in the blood of chronic, frequent cannabis users at low concentrations for as long as 30 days."

The users with longer-lasting traces of THC in their blood samples had what Huestis described as "huge body burdens," where THC would remain in their fat cells for extended periods of time due to the nature of the compound. "THC is lipophilic. It likes fat," she says.

In the Workplace

Before marijuana began to be legalized, it wasn't an issue the National Safety Council (NSC) had to address head-on. The NSC could point to U.S. federal law and advise employers to prohibit employees from using it.

After U.S. states began legalizing the drug—first for medical use and later for recreational use—many employers began dropping marijuana testing from their preemployment screening, says Jane Terry, vice president of government affairs at the NSC.

Employers who are hiring for safety-sensitive positions, such as truck drivers or pilots, continue to test potential and current employees for marijuana. This is because these positions are subject to U.S. federal regulations, often under the U.S. Department of Transportation, that require them to conduct drug testing.

"Truck drivers who have a Colorado license have to do testing, including for THC," Terry says. "That has not changed, but what we've seen from companies is there's an increasing presence in THC in those operators and the cultural idea that—in this legal change for the states in America—marijuana use is okay. It's affecting those who are required to be tested."

And this again poses difficulties—just because someone tests positive for usage does not mean that they are impaired, Terry adds.

"There is no scientific test for impairment of cannabis," she explains. "Policymakers and others think that because we can test for alcohol, it can be done for cannabis. But cannabis goes to your fat cells. Presence does not mean impairment—it can stick around for days or weeks. But because you can't test impairment, it is really challenging for employers to figure out how to react if someone is using on the job."

U.S. states that have legalized some reasons for marijuana use are creating more protections for employees who test positive for the drug. For instance, New Jersey enacted a law in July 2019 that prevents employers from refusing to hire individuals with a medical marijuana license. It also requires employers to give employees who do test positive for marijuana use the opportunity to provide a legitimate medical reason for testing positive.

But for employees who are fired for testing positive for marijuana use in a state that has legalized it, the courts remain divided because the drug is still considered illegal at the federal level. One of the first cases to demonstrate this was Coats v. Dish Network.

Brandon Coats worked for Dish Network as a telephone customer service representative from 2007 to 2010. Coats is a quadriplegic and has required use of a wheelchair since he was a teenager. After Colorado legalized the medical use of marijuana, Coats obtained a license to use marijuana to treat muscle spasms caused by his quadriplegia; he used the drug only while off-duty.

In May 2010, Dish had Coats take a drug test, and he tested positive for marijuana. Coats informed his employer that he was a registered medical marijuana patient and would continue using the drug. But in June 2010, Dish fired him for violating the company's drug policy.

Coats sued Dish for wrongful termination because under Colorado law, he was using marijuana legally during nonwork hours. In 2015, his case made it to the Colorado Supreme Court, which upheld his termination because marijuana is a Schedule I drug under federal law. The court interpreted this to mean that even employees who use marijuana in states that have legalized it are not protected by federal labor laws that would have prevented his termination.

"…'the Supremacy Clause unambiguously provides that if there is any conflict between federal and state law, federal law shall prevail,' including in the area of marijuana regulation," the court wrote. "Coats's use of medical marijuana was unlawful under federal law and thus not protected."

While the courts and legislators continue to grapple with the drug's legality, the NSC says more research is needed on cannabis to determine how it affects users and their ability to function when under the influence. But until that research produces actionable data, the NSC is advocating that people who hold safety-sensitive positions should not use marijuana—even when not at work, Terry says.

The NSC released a policy statement in October 2019 expressing its stance on marijuana in the workplace, because employees who tested positive for cannabis had 55 percent more industrial accidents, 85 percent more injuries and 75 percent greater absenteeism compared to those who tested negative.

"NSC believes it is unsafe to be under the influence of cannabis while working in safety-sensitive positions due to the increased risk of injury or death to the operator and others. Research is clear that cannabis impacts psychomotor skills and cognitive ability," the NSC said. "However, the amount of THC detectable in the body does not directly correlate to a degree of impairment. At this time, NSC believes there is no level of cannabis use that is safe or acceptable for employees who work in safety-sensitive positions."

And the NSC maintains that to create a safe work environment for all employees, employers should continue to prohibit employees from being under the influence of marijuana while on the job—regardless of whether they hold a safety-sensitive position or not.

To help create a drug-free workplace, the NSC says employers should have a drug policy that includes proper management training to make managers more likely to enforce the policy; access to support for employees with drug problems; clearly defined use and possession parameters for employees; established rules for post-accident testing; and rules on how to handle an employee's conviction or arrest.

"A drug policy must be very specific and supported by workplace procedures to reduce the chance of litigation," according to the NSC. "Drug policy and workplace procedures should be reviewed by a lawyer to ensure they comply with state laws. And policy must be updated frequently to keep up with changing laws and attitudes."

To help enforce these policies, Terry says employers are also looking for solutions where they can test for marijuana impairment on the job, as they can administer breathalyzer tests for alcohol impairment.

Two researchers at the University of Pittsburgh recently developed a similar test, which uses a device that incorporates nanotechnology and artificial intelligence to measure THC levels in a person's breath.

"At the heart of our technology is the sensor chip made of carbon nanotubes—it's 100,000 times smaller than a human hair," says Alex Star, a professor of chemistry at the University of Pittsburgh. "When molecules land on the surface of the carbon nanotubes, there's a change in their conductance…THC being less volatile than other components of human breath, other molecules can leave the surface of the chip faster, but the THC stays for a longer time."

Star and his research partner, Ervin Sejdic, associate professor of electrical and computer engineering at the University of Pittsburgh, worked on the device for three years and obtained permission from the U.S. Drug Enforcement Administration to purchase marijuana to conduct testing. They created the device and an artificial intelligence algorithm to help them understand what the device's measurements might mean.

"The computer model is getting trained on how those traces [of THC] would look," Star explains. "The machine learning can predict with greater accuracy if the THC is present or not. It's much more reliable than simply displaying the numbers that you're directly observing from the sensor."

However, Star echoes Huestis's expert opinion that just because THC is detected it does not mean that a person is impaired.

"What does the measurement actually mean? We're still figuring that out," Star adds. 

Megan Gates is senior editor at Security Management.

This article is adapted from Security Management magazine with permission from ASIS © 2019. All rights reserved.