- How is legalized marijuana affecting workplaces?
- How does marijuana affect cognition?
- Workplace Drug Testing Policy and Legalized Marijuana
- Common Questions About Marijuana and Workplace Drug Testing
How is legalized marijuana affecting workplaces?
91% of Americans agree with the relaxation of marijuana laws according to Pew Research. This comes after marijuana has already been fully legalized in 17 states. See map below:
Clearly, social and cultural attitudes towards marijuana are becoming increasingly positive and accepting. Over half of American adults have tried marijuana at least once in their lives and 22% of Americans (55 million) used marijuana at least once or twice in the past year. 35 million American adults use marijuana at least once or twice a month, according to a poll by Yahoo News and Marist University.
The same trend of growing marijuana acceptance is visible on a global-scale:
The implications of marijuana legalization on society, culture, and local economies are still debated.
There is little dispute, however, that increased marijuana use is a serious challenge for some businesses, such as those in safety-sensitive industries.
First of all, there seems to be a general lack of clarity on how to manage use of a drug that is legal at the state level, yet still illegal at the federal level.
Secondly, there is a lack of understanding about the level of impairment present at various stages of marijuana use, and to what degree a drug-test is capable of revealing that impairment as opposed to merely revealing a trace of THC that was consumed weeks prior.
Increasing positivity rate on marijuana tests pose new challenges to workplaces.
For workplaces erring on the side of caution, this typically brings some of the following challenges:
- Hiring: Workplaces are finding it more difficult to hire qualified candidates who can pass pre-employment drug screens that include THC.
- Turnover: Workplaces are having to fire more workers due to increased THC positivity on random drug-tests. Unfortunately, this often means dismissing highly qualified, valuable employees who are difficult to replace.
- Morale: Workplaces are suffering from reduced morale due to increased drug-related dismissals and the general incompatibility of workplace regulations with new cultural standards of marijuana use.
On the other hand, “More and more employers appear to be treating marijuana use like alcohol use and ignoring off-duty recreational use," says Anne-Marie Welch, an attorney with Clark Hill in Birmingham, MI. "She recommends that employers who decide to continue screening for marijuana mention their drug-testing requirement in job postings. This will help employers screen out candidates who can’t pass the test" (SHRM).
For workplaces taking a more progressive approach to accepting these cultural changes by relaxing drug-testing practices, the following challenges become apparent:
- Productivity: Workplaces are suffering from reduced productivity due to increased cannabis impairment among workers (see cognitive impacts of marijuana impairment below).
- Safety: Workplaces are suffering from increased safety risks and incidents due to increased cannabis impairment among workers. False positives or positive results due to marijuana use outside of work may also cut short post-accident root cause analyses, leading to other important risk factors being overlooked.
Of course, the COVID-19 pandemic has put even more pressure on workplaces to revise their drug-testing policies because of the labor shortage it has created:
“There’s a labor shortage in some industries due to COVID-19-related illnesses, unemployment subsidies, fear and child care issues. As a result, employers are grappling with finding qualified applicants,” says Welch (SHRM).
One solution that has worked in many industries is using real-time impairment testing, such as AlertMeter®, combined with traditional drug-testing.
Workplaces also have the option to utilize a medical review office, such as Cynergy MRO, to assess the results of a drug or impairment test.
With a third party reviewing cognitive impairment and drug test results, you can account for important factors such as:
- amount of cannabis in the system
- employee medical history
- current visible impairment
- physician attestation for medical marijuana users, and more.
Together, real-time impairment testing and the utilization of a medical review office can ensure increased workplace safety and reduced employer liability. To learn more about how AlertMeter® real-time impairment testing and Cynergy Medical Review Office can improve your workplace drug-testing program, click here.
One of the reasons safety-sensitive workplaces struggle to establish a workplace marijuana policy that retains quality employees and filters out the impaired may be due in part to the misunderstandings regarding the cognitive effects of marijuana use. The next section will provide a review of the latest research on the cognitive effects of marijuana.
How does Marijuana affect cognition?
When Brandon Coats was 16-years old, he was a passenger in a vehicle that crashed into a tree. The accident left 80% of his body paralyzed.
Wheelchair-bound, Brandon got a job as a customer service representative for DISH in 2007. Meanwhile, his prescription medicine for involuntary muscle spasms had grown less effective over the years. So, Brandon's doctor recommended he try medical marijuana. He got his medical marijuana card in 2009 and found that it did in fact alleviate his symptoms.
A year later, he was administered a random drug test. He tested positive for THC and, despite holding a medical marijuana card and never using marijuana while at work, he was dismissed from his job.
In 2015, the Colorado Supreme Court ruled in favor of DISH, citing that although medical marijuana was legal in Colorado at the time, it was still illegal federally.
(This story was originally reported by Westword.)
Despite winning in the court, DISH lost a valuable employee that day. They also set an unsustainable precedent by disallowing hundreds of thousands of medical marijuana users from seeking employment in a non-safety sensitive position within their company.
If this is such a contentious issue for non-safety sensitive workplaces, what can safety-sensitive industries who are even more pressed for quality employees do?
First, they must learn to look beyond the positive or negative result of a drug-test and focus on the actual culprit: impairment. After all, a positive drug-test doesn't necessarily mean that an employee is impaired at work and a negative drug-test doesn't necessarily mean that they aren't a serious safety risk in your workplace.
Consider the following research on cognitive impairment due to marijuana use. Note the high level of variability based on the type of user, the length of use over a lifetime, time since use, the frequency of use, etc.
According to this table, cognitive functions that are critical to the ability of a safety-sensitive worker to be safe and productive can be affected to varying degrees after marijuana use. For example, the ability of your worker to remember where you just told him the emergency brake was may be impaired if he consumed marijuana within the past 6 hours. If it's been over 7 hours, however, he might remember in time to pull it. If it's been over 3 weeks since he consumed marijuana, he might not get a positive drug-test or feel impaired, but he might make the very poor decision to climb a scaffold without a harness or start a forklift jousting competition:
For a more complete understanding of "fitness-for-work" in the age of legalized marijuana, let's review the research on how THC affects several of the cognitive functions that must be in optimal working order for safety-sensitive workers.
How does marijuana use affect short-term memory?
- Cannabis consumption impairs "the ability to hold and manipulate information and remember it following a short delay" (Tinklenberg et al., 1970; Miller et al., 1977; Heishman et al., 1997).
- In a study of chronic cannabis users, "acute intoxication resulted in significant impairment in working memory, and subjects receiving a higher dose of THC (3.9%) took significantly longer to complete the task" (Hart et al., 2001).
- "Chronic users of cannabis have altered memory-related brain activation in the form of dysfunctional SME production and/or poorer neural efficiency, which is associated with deficits in memory recall" (Shrivastava, et.al., 2011).
How does marijuana use affect decision-making and judgment?
- There are potential differences in risky decision-making between frequent marijuana users and non-users, "but it is uncertain whether these differences are pre-existing and increase vulnerability for frequent marijuana use or if they are related to the effects of frequent MJ use on decision-making" (Casey, Cservenka, 2020).
- "Cannabis users showed significant impairments on quality of decision-making and executive planning" (Grant et al., 2012).
- "Marijuana users demonstrated relative cognitive impairments in verbal memory, spatial working memory, spatial planning, and motivated decision making " (Becker et al., 2014).
- "Marijuana users are more likely to make risky judgments despite subsequent monetary punishment than healthy controls" (Grant et al., 2012)
- "Marijuana users demonstrate less flexibility and abstract reasoning ability than non-users and decision-making tends to be more risky" (Clark, Roiser, Robbins, & Sahakian, 2009; Solowij et al., 2012).
Although these studies and others disclose that decision-making impairment differs between chronic and acute use, there seems to be consensus that, in general, marijuana use does impair judgment and decision-making skills. In a safety-sensitive workplace, even the slightest impairment in judgment can quickly become disastrous. Take USAir Flight 405, for example:
On March 22, 1992, USAir Flight 405 arrived at gate B1 at LaGuardia Airport, New York to pick up 69 passengers headed for Cleveland, Ohio. It was delayed 1 hour and 6 minutes in getting there due to congestion in the airport's taxiways.
As it was a snowy day in New York, the plane was deiced. After one of the deicing trucks experienced mechanical problems and blocked the plane's exit, the flight was delayed another 20 minutes. At this time, another deicing was requested.
Due to the weather and heavy traffic, the flight was delayed another 20-40 minutes by the time it reached the runway.
With regulations requiring deicing every 20 minutes, the first officer checked the wings for ice several times as they awaited take-off. At one point, the first officer asked, "Look at all that stuff. What is that?" to which the pilot replied, "Sand I guess, urea sand." Later, the captain of the flight behind them in the taxiway remarked that the plane appeared to be clear of ice.
"The captain was faced with quite a problem. If he wanted to be deiced a third time, he would have had to get out of the line [of jets waiting to take off] and taxi all the way back to the parking area and meet up with a deicing truck again. That would have put him very, very late, and it may have even caused the cancellation of the flight." (NTSB report)
The pilot did not assess any serious risk and, wanting to get his passengers to their destination, decided that it was safe to take-off without a third deicing. A few seconds later, the pilot had gotten the undercarriage to lift off the runway, but the plane only got several meters high before it crashed back to the ground and slid into the Flushing Bay. 24 of the 69 people onboard were killed.
Neither cannabis nor any other source of cognitive impairment was identified as a contributing factor in this tragic accident. However, it is a good example of the importance of optimum decision-making skills in a safety-critical environment--especially when something has already gone wrong such as bad weather or long delays.
Poor decisions and human error are difficult to pinpoint in the aftermath of an accident. It's much easier to blame adverse weather, malfunctioning equipment, or poor safety procedures.
The depth of investigation required in the aftermath of an aviation incident, however, has allowed for the understanding that "somewhere between 60-80% of aviation accidents are due, at least in part, to human error" (Shappell & Wiegmann, 1996).
If this comes from an industry in which worker health and alertness is much more regulated than in other safety-sensitive industries, consider how many other industrial accidents who undergo less thorough investigations would uncover human error and impairment as a root cause or contributing factor.
The profound reduction in accident rate, severity, and costs after workplaces implement cognitive impairment testing may serve as a good indicator of the extent to which poor decision-making due to cannabis, stress, or fatigue contribute to workplace accidents:
- 20% - 35% Overall Reduction of Accidents
- 15% - 55% Reduction in Costs of Accidents
- 25% - 70% Reduction in Worker’s Comp Claims
How does marijuana use affect reaction time?
Another of the most detrimental effects of marijuana is potential reduction in reaction-time.
In a safety-sensitive industry, if reaction time is impaired, a lot can go wrong very quickly. In the Exxon Valdez oil spill, the third mate in charge of steering the vessel away from a reef took just a couple minutes too long after being told to start maneuvering. Although the reason for the delayed reaction wasn't clear (sleep deprivation may have played a role), the difference in minutes resulted in extreme wildlife and habitat destruction and millions of dollars worth of damage. Every day, truck drivers must react quickly to avoid other drivers or obstacles on the road; construction workers must react quickly to assist a coworker in danger; manufacturers must react quickly to turn off malfunctioning equipment, etc.
The effects of marijuana on reaction time are still being studied. However, existing studies tend to conclude that reaction time is significantly impaired after marijuana use, and that the higher the dose of marijuana, the greater the impairment:
- In a small study of experienced marijuana users: "Linear movement time was significantly reduced after smoking marijuana, while rotary movement time was not significantly affected; error rates for the two types of motor movements increased significantly and especially for linear movements as the dose level increased" (Kvålseth,1977).
- "Reaction time performance may involve two phases: an early, attention-demanding phase which is sensitive to drug effects and a later, 'automatic', phase which results from practice and is more resistant to drug effects" (Peeke, 1976).
- In a study measuring cannabis' impact on simulated arterial driving, "High dose cannabis was associated with decreased mean speed, increased mean and variability in headways, and longer reaction time" (Lenné, 2010).
- From another study on cannabis and driving, "Experimental data show that drivers attempt to compensate by driving more slowly after smoking cannabis, but control deteriorates with increasing task complexity. Cannabis smoking increases lane weaving and impaired cognitive function. Critical-tracking tests, reaction times, divided-attention tasks, and lane-position variability all show cannabis-induced impairment. Despite purported tolerance in frequent smokers, complex tasks still show impairment" (Hartman, 2012).
- In a study measuring how long it took an intoxicated driver to avoid an accident: "Both alcohol and marijuana treatment significantly increased crash avoidance reaction time" (Alali, 2020).
- "[High-potency marijuana (13% THC)] significantly increased stop reaction time and the proportions of commission and omission errors in the Stop signal task (see below). THC-induced impairments lasted up to 6h postsmoking" (Ramaekers, 2006).
"The participant must respond to an arrow stimulus, by selecting one of two options, depending on the direction in which the arrow points. If an audio tone is present, the subject must withhold making that response (inhibition).Outcome measures cover direction errors, proportion of successful stops, reaction time on Go trials, and stop signal reaction time (SSRT)" (Cambridge Cognition)
How does marijuana use affect vigilance and attention?
According to Al-Shargi, "vigilance can be defined as the ability to sustain attention and remain alert to a particular stimulus over a prolonged period of time" (2019).
The effects of marijuana use on vigilance and attention have mostly been studied within the context of adolescent attention span and schoolwork. However, vigilance and attention are also extremely important when considering the daily routines of a safety-sensitive worker.
Many 24/7 operations, 911 operators and emergency dispatchers, security personnel such as prison guards, must sustain a high level of vigilance even when work is monotonous or slow. Their ability to stay vigilant and focused through long, dull night-shifts is extremely critical.
Whether due to fatigue or cannabis, it is imperative that workplaces are aware of the risks caused by impaired attention and vigilance at work.
- "Inhalation from cannabis joints leads to a rapid increase in blood THC with a delayed decrease in vigilance and driving performance, more pronounced and lasting longer in occasional users than in chronic users" (Hartley, 2014).
- "There is increasing evidence that cannabis intoxication negatively affects basal cognitive functions like episodic memory, attentional control, and motor inhibition" (Kroon, 2021).
"Marijuana subjects showed decreased activation in the normal attention network...The greater activation in the precuneus with increasing visual attentional load in both groups of marijuana users suggests that these subjects require greater attentional modulation in this brain region than the non-drug users. This increased usage of the reserve network might lead to a decreased capacity to perform even more cognitively demanding tasks" (Chang, 2006).
Again, there is evidence that marijuana use leads to reduced attention and vigilance. However, factors such as amount of use, frequency of use, and type of user (chronic vs occasional) complicate our ability to fully understand the extent of the attention detriment.
If a worker cannot score within his normal range of alertness on this 60 second test, he may be too impaired to work. The test does not identify the cause of impairment--cannabis, fatigue, stress, alcohol, etc.--so whilst protecting worker privacy, the test provides an accurate assessment of cognitive detriment due to any cause, in real-time.
Workplace Drug Testing Policy and Legalized Marijuana
Even though marijuana has been legalized in many US states, safety-sensitive workplaces still have zero-tolerance policies for marijuana and other drugs. Depending on the industry and where the company is located, workplaces utilize a variety of testing methods for marijuana.
Since THC can linger in the human system for 3 weeks or longer, many workplaces wonder if it's fair to fire an employee who got a positive result on a random drug test even though he hadn't consumed marijuana any time recently. If you share this concern, consider the following testing methods to better understand their strengths and weaknesses and identify areas for improvement:
1. Marijuana and Pre-Employment Drug Testing:
Pre-employment drug tests that include THC testing may be effective if your goal is to exclude chronic or habitual marijuana users from your workforce. However, this may also include people who use medical marijuana to manage chronic pain/disorders and enable them to perform better at work than they could without it. An important factor to consider is that if a potential employee cannot abstain from smoking long enough to avoid a positive test result, they may not be able to abstain around work hours either. Unless the use is for medical purposes, not abstaining may also indicate a general lack of concern on the worker's part. If you are willing to hire a medical marijuana user who consumes in a way that does not impact their ability to work safely, you may utilize a medical review office to assess positive test results and provide physician attestation that the candidate is, in fact, medically required to consume marijuana.
2. Marijuana and Random Drug Testing:
Random drug testing can be an effective method of deterrence and an effective way to enforce your zero-tolerance drug policy. However, its efficacy relies on being utilized frequently and in an unpredictable manner. This means workplaces must invest quite a lot of time and money to frequently conduct these tests. If your workplace is in a remote location, this could become a real productivity killer. However, if testing becomes too infrequent, workers will not be sufficiently deterred. On the other hand, testing too frequently may contribute to reduced workplace morale and higher turnover. Few workers like being told to urinate in a cup. Even fewer like it when they suspect that the testing isn't "random" and they're being singled out.
3. Marijuana and Post-Accident Drug Testing:
There is a growing trend of positivity in post-accident drug-tests. The latest statistic states that 78% of post-accident drug-tests are positive for marijuana. However, it is important to consider whether this relationship is causal or correlational. Is increased marijuana consumption causing more accidents? Or are there more positive test results due to increased consumption on weekends, without interference with work hours? It is paramount to safety that workplaces are able to answer this question in their root-cause analyses.
One option is to utilize a Medical Review Office to gather more information about the amount of cannabis in the system at the time of the accident and what level of impairment it may have been associated with. If there was a trace amount of THC indicating use several days/weeks ago, it might not make sense to attribute the accident to marijuana use. If there is a high amount of THC still detectable in the system, marijuana impairment likely played a role.
A more proactive option is to use real-time impairment testing before workers begin their shifts or undertake a critical task. Via a 60-second test, you can identify workers who may be impaired or struggling to stay alert. If, after speaking to the worker, you have reasonable suspicion that the worker is currently intoxicated, you can order a drug-test and find out about marijuana impairment before it leads to an accident.
This leads us to the fourth type of drug testing:
4. Marijuana and Reasonable Suspicion Testing:
The success of reasonable suspicion testing relies largely on the confidence level of a supervisor or manager engaging with the employee demonstrating signs of impairment. Often reasonable suspicion goes unreported, only to be recognized later in the form of an incident or injury. Adequate training and communication skills are essential if you are relying heavily on reasonable suspicion testing.
Alternatively, you can enlist the services of Cynergy MRO, a medical review office who will conduct a quick telehealth visit with workers who are identified as potentially impaired by the AlertMeter® test.
The medical review office will be able to determine whether there is reasonable cause to order a drug-test, whether the employee requires medical attention, or if he/she can safely continue work. It's a great way to reduce liability and increase confidence in your workers' ability to work safely.
5. Marijuana and Cognitive Impairment Testing:
As mentioned, one of the disadvantages of traditional drug-testing is its inability to identify impairment in real-time.
A drug-test is purely a measure of whether a substance was consumed at any time in the recent past, to the level that it can still be detected in the bloodstream, hair, or urine. The test provides no further insight about whether the worker smoked weeks ago or if they are currently cognitively impaired.
A cognitive impairment test fills this gap. It measures subtle differences in how a worker with an established baseline performs on tasks that measure reaction time, accuracy, vigilance, pattern recognition, and short-term memory.
If it detects significant differences in the worker's performance on these tasks, it tags the worker as "outside normal range of alertness".
This triggers a notification to a supervisor who then speaks with the worker to determine if there is an active safety risk.
Many times, the worker is fatigued, dehydrated, or stressed and needs a break, a snack, or a drink of water before they can resume work. Other times, the supervisor will conclude reasonable suspicion and refer the worker to HR or follow company protocols.
The AlertMeter® is the only accurate cognitive impairment test that can identify potentially impaired workers in 60-seconds. It is a simple, graphics-based test that all worker can take with ease regardless of age, technical skill, language, or education. Workers appreciate the fact that it is non-invasive and doesn't violate worker privacy in any way.
Common Questions About Marijuana and Workplace drug testing
1. What happens if a worker smokes on a Friday night and then gets a random test on Monday which comes up positive?
It depends on your company policy. However, one of the manufacturing companies who uses AlertMeter® (click here to hear their story) actually eliminated random drug testing for this reason. The company is located in Colorado, where marijuana is legal. The employee had smoked on the weekend and got random drug-tested on Monday. He came up positive and had to be fired per company policy. The employee had worked there for 20 years and operated really complex machinery. It took over a year to find another worker with the skills and qualifications needed to replace him. It also damaged morale since they fired one of their best and most loyal employees. The company decided to get AlertMeter® and totally ended their random drug-testing program, reducing drug-testing costs in the process. They are still able to maintain a zero-tolerance drug policy.
2. Can you use medical marijuana and still work in a safety-sensitive job?
One of the issues with legal marijuana is that unfortunately, medical marijuana cards are often not written by or monitored with regularity by a primary care physician. If someone is in a safety-sensitive position, the physician who signed off on the use should verify that the person with the card is able to perform their safety-sensitive job duties, and what restrictions on use would be applicable based on the condition for which the referral was given.
There is a gap in accountability for physicians referring marijuana use for a medicinal purpose. Data shows that medicinal marijuana, along with a number of other legal prescription drugs, do not fit well in an environment where there is a particular need for safety. A Medical Review Officer plays a key role in this area of accommodation vs. safety.Cynergy MRO: "We recently instituted a medicinal marijuana attestation process for non-regulated drug screens. We can help you make the decision when you’re considering whom to hire, and under what accommodation practice. After that, you can use AlertMeter® as a daily process. If you utilize both services--a physician verifying appropriateness of use before employment, and AlertMeter® to ensure daily fitness, you have a high level of risk mitigation in place."
3. Isn’t cognitive impairment testing a bit invasive? How do we get the staff to take the test?
Would your employees rather play a 60 second game or urinate in a cup?
There is nothing within the AlertMeter® app that requires private or sensitive employee information. Essentially, all the test does is prompt a quick conversation between a supervisor and a potentially impaired employee. What you do after that follows existing company protocol, exactly what you're currently doing during a stretch and flex or another in-person exercise for supervisors to detect impaired workers. This is just a faster and more objective way of doing it. We have overwhelmingly positive feedback from workers and supervisors who have used this.
Thankfully, with the legalization of marijuana has come new and improved ways to detect worker impairment and improve workplace safety. Comprehensive MRO services for pre-employment screening prevents a catastrophic hire. Daily fit-for-work assessment tools like AlertMeter® create a culture of safety and trust among co-workers that they are in a drug safe working environment. The MRO ensures that the daily screening and application of policy are assessed fairly and equally across the employee population, giving supervisors and employees a high level of trust in the equity of the process. The partnership between the employer, the MRO, the technology, and the employees is a winning combination for your business.
Click here to listen to a webinar about how you can utilize AlertMeter® and Cynergy for increased confidence in your workforce, improved safety, improved morale, decreased costs, and decreased liability.
Alali K, Stewart J, Taneja R, Nwobi E, Commissaris R, et al. (2020) Marijuana and alcohol increase crash avoidance reaction time in a driving simulator test at blood concentrations below commonly-used per se ‘Cut-offs’ for Intoxication. J Addict Med Ther Sci 6(1): 009-015. DOI: 10.17352/2455-3484.000030
Al-Shargie, F., Tariq, U., Mir, H., Alawar, H., Babiloni, F., & Al-Nashash, H. (2019). Vigilance Decrement and Enhancement Techniques: A Review. Brain sciences, 9(8), 178. https://doi.org/10.3390/brainsci9080178
Chait, L.D. Subjective and behavioral effects of marijuana the morning after smoking. Psychopharmacology 100, 328–333 (1990). https://doi.org/10.1007/BF02244601
Emese Kroon, Lauren Kuhns, Janna Cousijn, The short-term and long-term effects of cannabis on cognition: recent advances in the field, Current Opinion in Psychology, Volume 38, 2021, Pages 49-55, ISSN 2352-250X, https://doi.org/10.1016/j.copsyc.2020.07.005.
Hartley S, Simon N, Larabi A, Vaugier I, Barbot F, Quera-Salva MA, Alvarez JC. Effect of Smoked Cannabis on Vigilance and Accident Risk Using Simulated Driving in Occasional and Chronic Users and the Pharmacokinetic-Pharmacodynamic Relationship. Clin Chem. 2019 May;65(5):684-693. doi: 10.1373/clinchem.2018.299727. Epub 2019 Mar 14. PMID: 30872375.
Hartman RL, Brown TL, Milavetz G, et al. Cannabis effects on driving lateral control with and without alcohol. Drug Alcohol Depend. 2015;154:25-37. doi:10.1016/j.drugalcdep.2015.06.015.
Hartman RL, Huestis MA. Cannabis effects on driving skills. Clin Chem. 2013;59(3):478-492. doi:10.1373/clinchem.2012.194381.
Kvålseth TO. Effects of marijuana on human reaction time and motor control. Percept Mot Skills. 1977 Dec;45(3 Pt 1):935-9. doi: 10.2466/pms.19184.108.40.2065. PMID: 600655.
L. Chang, R. Yakupov, C. Cloak, T. Ernst, Marijuana use is associated with a reorganized visual-attention network and cerebellar hypoactivation, Brain, Volume 129, Issue 5, May 2006, Pages 1096–1112, https://doi.org/10.1093/brain/awl064
Lenné MG, Dietze PM, Triggs TJ, Walmsley S, Murphy B, Redman JR. The effects of cannabis and alcohol on simulated arterial driving: Influences of driving experience and task demand. Accid Anal Prev. 2010;42(3):859-866. doi:10.1016/j.aap.2009.04.021.
Peeke SC, Jones RT, Stone GC. Effects of practice on marijuana-induced changes in reaction time. Psychopharmacology (Berl). 1976 Jul 28;48(2):159-63. doi: 10.1007/BF00423255. PMID: 826928.
Ramaekers, J., Kauert, G., van Ruitenbeek, P. et al. High-Potency Marijuana Impairs Executive Function and Inhibitory Motor Control. Neuropsychopharmacol 31, 2296–2303 (2006). https://doi.org/10.1038/sj.npp.1301068
Shrivastava, A., Johnston, M., & Tsuang, M. (2011). Cannabis use and cognitive dysfunction. Indian journal of psychiatry, 53(3), 187–191. https://doi.org/10.4103/0019-5545.86796