Cannabis and Work: Implications, Impairment, and the Need for Further Research

Posted on by John Howard, MD; L. Casey Chosewood, MD; Lore Jackson-Lee, MPH; and Jamie Osborne, MPH, CHES®


American workplaces are facing unprecedented challenges related to the rapidly evolving landscape of cannabis legalization and its increasing use among workers. Cannabis[1] is the most frequently used illicit drug (by Federal law) among Americans, with an estimated 43.5 million past-year users age 12 or older in 2018 (1). Nearly 18% of adults employed full-time, and nearly 21% of adults employed part-time, reported using cannabis during the previous year. The implications for workplace safety are emerging, as well as concerns about impairment, risk of injury, recruitment and hiring, regulatory issues, and the overall health and well-being of both workers and the public.

Federal and State Status

The Controlled Substances Act administered by the U.S. Drug Enforcement Administration currently classifies marijuana as a Schedule I substance, meaning that it has no accepted medical use and has a high potential for abuse (4). Substances that are classified as Schedule I have the most regulatory restrictions, and thus there are strict limits on researchers’ access to study marijuana and explore its potential medicinal value and public health and safety impacts. Regardless of the federal prohibition of marijuana, 33 states* as well as Washington D.C., Guam, Puerto Rico, and the U.S. Virgin Islands have passed laws legalizing marijuana for medicinal and/or non-medical adult uses at the time of this publication (5).

Work and Safety

While data on marijuana use and workplace safety and health is limited, there is evidence suggesting workplace risks and burdens associated with the drug’s use. Studies of cannabis have demonstrated effects that include sedation, disorientation, impaired judgment, lack of concentration, and slowed fine motor skills, all of which can contribute to delayed decision-making, impaired learning, and memory and attention deficits (6). One such study, reported by the National Institute on Drug Abuse (NIDA), found 55% more industrial accidents, 85% more injuries, and 75% greater absenteeism among employees who tested positive for marijuana compared to those who tested negative (6). Research has also demonstrated a statistically significant association between marijuana use and increased risk of motor vehicle crashes (2,3). The National Safety Council (NSC) released a position statement in 2019 stating that “cannabis impacts psychomotor skills and cognitive ability” and “there is no level of cannabis use that is safe or acceptable for employees who work in safety-sensitive positions” (7). However, not all research is as conclusive about the relationship between marijuana use and occupational injury. A systematic review published in May 2020 found that the current body of literature does not provide sufficient evidence that marijuana users are at increased or decreased risk for occupational injury, and that further high-quality research is needed to eliminate study biases and provide clarity on causality (8).


NIOSH recognizes the challenges associated with detecting impairment from marijuana, especially when compared to other substances like alcohol. Impairment from marijuana varies with THC concentration or dose, route of administration, and users’ experience with, or tolerance to, the drug (9). Since marijuana is stored in the fatty tissue, it can be detected through drug testing several days or weeks – long after the individual has stopped experiencing any physiological effects and impaired functioning. The THC levels that create impairment are not well understood and according to the NIDA, there is wide variability in how THC is metabolized by frequent users versus infrequent users which makes interpretation of a positive urine drug test a challenge (10). NIOSH is currently developing information and resources on the topic of impairment testing as a potential adjunct or alternative to certain forms of workplace drug testing. Impairment testing evaluates a worker’s real-time cognitive function and motor skills to determine if there is evidence that the worker may be impaired, regardless of the source of impairment. It is theorized that, compared to traditional workplace drug testing, impairment testing may provide more immediate, actionable, accurate, and comprehensive information, allowing employers to be more proactive in minimizing risks in the workplace while maintaining more privacy and fairness for workers. Research efforts to explore this issue further are of great interest to NIOSH as we develop related content and resources.

Workers’ Compensation

In addition to direct worker safety and health issues, the changing landscape of marijuana legalization and use also has important implications for workers compensation. The impact of marijuana use on workers compensation claims varies from state to state and even organization to organization. NIOSH is exploring workers compensation issues pertaining to marijuana, including but not limited to:

  • determination of impairment at the time of an injured worker’s accident;
  • impact on a worker’s compensation claim if employee tested positive for state-approved and/or physician-recommended medical marijuana at the time of an accident; and
  • potential for reimbursement for medical marijuana used to treat a work-related injury.

According to the National Council on Compensation Insurance (NCCI), most jurisdictions have workers compensation laws that, in some form, restrict workers compensation benefits when the injury is attributed to intoxication or drug use (11). Interestingly, some research suggests that medical marijuana could have a positive impact on worker safety and health. Medical marijuana may allow workers to better manage pain and other symptoms associated with workplace injuries and illnesses, reducing worker’s compensation claims (12) and the use of opioids (13-15). However, further research, including more comprehensive and long-term studies, are needed to better understand these relationships.

Knowledge Gaps

Despite the evolving landscape of legalization and commercialization, there are gaps in the knowledge guiding workplace policies surrounding marijuana, including those related to worker safety and health and privacy and confidentiality issues. We must work to address research barriers, fill research gaps, and improve research quality and surveillance capacity. Research on the association between cannabis use and occupational safety and health needs to be explored across different populations, occupations, workplace settings, worker characteristics, and work patterns. Research should also focus on understudied demographics, including working adolescents and employed older populations. Similarly, the evolution of marijuana legalization and use presents several critical considerations for employers, including, but not limited to:

  • comprehensive impairment policies and testing methodology;
  • state antidiscrimination or reasonable accommodation provisions for state-approved medical marijuana;
  • awareness and delegation of safety-sensitive roles and tasks; and
  • employer liability.

NIOSH will also continue to conduct research and Health Hazard Evaluations (HHEs) specific to worker safety and health in the rapidly expanding marijuana production and retail industry sectors.


Like any emerging hazard with worker and workplace implications, the rise in marijuana use among workers deserves critical review, additional research and a deeper understanding. It is vital to examine this issue through the lens of occupational safety and health, and to prepare for the inevitable and continuous changes to come. NIOSH is taking crucial first steps in examining this topic and welcomes input and recommendations from its stakeholders.


John Howard, MD, is the Director of the National Institute for Occupational Safety and Health (NIOSH).

L. Casey Chosewood, MD, is the Director of the NIOSH Office for Total Worker Health®.

Lore Jackson-Lee, MPH, is the Associate Director for Policy, Planning, and Evaluation at NIOSH.

Jamie Osborne, MPH, CHES® is a Public Health Analyst with the NIOSH Office of Policy, Planning, and Evaluation.


*error corrected 6/23/2020 (changed 34 to 33 states)


  1. 2018 NSDUH Annual National Report
  2. The Health Effects of Cannabis and Cannabinoids
  3. Marijuana and Public Health
  4. 21 U.S.C. Chap 13, § 801 et seq. at
  5. State Medical Marijuana Laws
  6. NIDA Report: Marijuana
  7. NSC Policy/Position Statement: Cannabis Impairment in Safety Sensitive Positions
  8. Wade R. Biasutti, Kurt S. H. Leffers & Russell C. Callaghan (2020): Systematic Review of Cannabis Use and Risk of Occupational Injury, Substance Use & Misuse, DOI: 10.1080/10826084.2020.1759643
  9. Phillips, J. A., Holland, M. G., Baldwin, D. D., Gifford-Meuleveld, L., Mueller, K. L., Perkison, B., … Dreger, M. (2015). Marijuana in the Workplace: Guidance for Occupational Health Professionals and Employers: Joint Guidance Statement of the American Association of Occupational Health Nurses and the American College of Occupational and Environmental Medicine. Workplace Health & Safety, 63(4), 139–164.
  10. NIDA News Release: Research on THC blood levels sheds light on difficulties of testing for impaired driving
  11. National Council on Compensation Insurance
  12. Ghimire KM, Maclean JC. Medical marijuana and workers’ compensation claiming. Health Economics. 2020;1–16.
  13. Bradford AC and Bradford WD. 2016. “Medical Marijuana Laws Reduce Prescription Medication Use in Medicare Part D,” Health Affairs 35, no. 7 (2016): 1230–1236.
  14. Bradford AC, Bradford WD, Abraham A, Bagwell Adams G. Association Between US State Medical Cannabis Laws and Opioid Prescribing in the Medicare Part D Population. JAMA Intern Med. 2018;178(5):667–672.
  15. Wen H, Hockenberry JM. Association of Medical and Adult-Use Marijuana Laws with Opioid Prescribing for Medicaid Enrollees. JAMA Intern Med. 2018;178(5):673–679.

[1] The terminology used to describe the cannabis plant, its components, and the physiological impacts of the different compounds in the plant are complex and contribute to much of the confusion surrounding it. Cannabinoids refer to the many chemical compounds unique to the cannabis sativa plant. Delta-9-tetrahydrocannabinol, or THC, is the main psychoactive cannabinoid, which gives users the “high” associated with the plant, and cannabidiol, or CBD, is the main non-psychoactive cannabinoid. Cannabis sativa that has high levels of THC and lower levels of CBD is referred to as “marijuana” (2,3). In this blog, marijuana will be used to refer to the Cannabis plant and to the THC-containing drug made from the plant.


Posted on by John Howard, MD; L. Casey Chosewood, MD; Lore Jackson-Lee, MPH; and Jamie Osborne, MPH, CHES®

19 comments on “Cannabis and Work: Implications, Impairment, and the Need for Further Research”

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

    This is an excellent essay. There is no doubt that compounds containing THC have the great potential to cause impairment and therefore a dangerous situation in the workplace. I anxiously await further information regarding impairment testing. Thank you!

    Research results in cannabis must not be taken for granted. Cannabis industry and its people must be open about it because it is one factor to consider in order to improve the manner of providing quality service.

    Thank you for you comment.

    Thank you for discussing this emerging serious problem. Cannabis use is increasing, and along with it impairment impacting work place safety. There is an excellent (while older) body of research using placebo double blind controlled studies showing impairment of the visual system with acute low dose marijuana use. The primary authors are Anthony Adams, Quinella Portnoy Hagerstrom and Mert Flom. We have had ability to do IRB approved opportunistically dosed studies identifying significant impairment of the visual field with acute marijuana use. This along with studies published in JAMA showing dysfunction of the neural retinal cell response using ERG…. clearly provides evidence that there is visual impairment. For many jobs, if one cannot see accurately, one cannot perform safely. Further research (ideally with placebo double blind controlled studies using real life marijuana) needs to be done….

    Dr. Valenti, thank you for your comment about the importance of visual acuity in ensuring workplace safety. As you point out, the literature about the effects of cannabis on vision begins in the 1970s. The following paper is an example of the literature you draw our attention to: Adams A.J. (1978) Acute Effects of Alcohol and Marijuana on Vision. In: Cool S.J., Smith E.L. (eds) Frontiers in Visual Science. Springer Series in Optical Sciences, vol 8. Springer, Berlin, Heidelberg,

    Overall, I thought this was a really interesting take on cannabis in the workplace. I think that as we start to learn more about the long term side-effects of cannabis use, it will be easier for employers to make decisions regarding the use of employees using, whether that’s recreational or medicinal. In my opinion, it’s much harder to determine whether or not an employer has the right to make a decision about someone’s medical wellbeing but we’ll just have to see in the coming years.

    Thank you for your comment. Indeed, we are just at the beginning of understanding the role of cannabis and the workplace. We hope that researchers take up the challenge of furthering our understanding.

    Please do continue to evaluate and analyze the effects of legalization – of both medical and recreational use of marijuana – on workplace safety. As usage increases across populations, and as testing guidelines for cannabis are removed due to privacy and protection issues, we need to thoroughly understand how these changes will affect worker safety and public safety. Marijuana can significantly impair judgment, motor coordination, and reaction time. Studies show that chronic (more than twice per week) usage has negative impacts on brain function, including on memory and the ability to plan and execute tasks. See

    We are already seeing the removal of marijuana testing from annual and random drug test protocols – even in industries such as construction! IMPACT (Ironworker Management Progressive Action Cooperative Trust) has released a statement that can be summarized like this: their “Drug-Free Work Force Program” will no longer require the testing for THC or marijuana and all penalties for members who test positive for those drugs have been eliminated. They state that employers should use “evidence of impairment on the job” to make employment decisions.

    Industries in which workers perform safety sensitive tasks, such as operating heavy equipment, should maintain their zero-tolerance stance towards drug use, including marijuana. Employers whose employees perform these tasks need to continue to test – regardless of legalization – on pre-employment, post-accident, and random bases. It is distressing to see a cooperative trust – the intersection of labor unions and management – remove the requirement for THC/marijuana testing. I believe the government can help protect workers and the public by transparently continuing research and offering strong guidelines to labor unions, employers, and the public regarding the impact of marijuana usage on the human body. Thank you.

    Thanks very much for your comment and for elevating ongoing concerns about the intersection of work, substance use, safety, and impairment. NIOSH recognizes that addressing cannabis use amongst workers, drug testing, and appropriate workplace policies is challenging and seeks additional assistance in answering questions related to the impact cannabinoid consumption has on occupational safety and performance and what evidence-based cannabis-related workplace policies can be recommended. By further investigating these issues, NIOSH researchers and partners hope to offer worker and employer recommendations supported by data-driven evidence.

    Guys, from a job hunter in the engineering field, it’s become harder to pass the pre-employ urine test. Some employers are actually lost on this subject and tested me for 20 vs 50 ng level of THC in the urine. They STILL think this is uncovering impairment! This has the effect of eliminating a good candidate who isn’t a chronic user, yet has a small amount excreted in urine that you all know lingers for over 10 days. I sure do appreciate what the IMPACT people did. It’s an about face to a decades-old misappropriate test. Perhaps when a real fair test is created, they and all of us will be able to use that and still leave the public’s life private as long as they are not endangering others at work.

    Thank you for your comment on the lack of correlation between a positive cannabis urine test and cognitive or behavioral impairment. In the absence of a standardized impairment test for cannabis impairment like the breath test for ethyl alcohol, employers still rely on the urine test. As you point out, reliance on urine testing for cannabis metabolites confuses non-impairing use with actual impairment.

    As an Australian, it’s great to know that cannabis can only be prescribed by TGA authorized prescribers to ensure safety. Americans are facing increasing challenges regarding cannabis legalization and its impact on workplace safety. It’s important to understand the implications for both workers and the public to make informed decisions. It’s crucial to focus on more research to improve knowledge gaps and develop comprehensive policies that address worker safety and health issues.

    Great post! The legalization of cannabis has significant implications for the workplace, including potential impairment and the need for further research to understand its effects better. Employers must update their workplace policies to address cannabis use responsibly while considering employee rights and safety concerns. Further research is essential to develop standardized testing methods for impairment and to inform evidence-based workplace policies on cannabis use.

    Thanks for your comments Jason. We agree with you that this is an important, rapidly-evolving issue. Additional research and policy work is essential to keeping workers and our workplace as safe as can be.

    The intersection of cannabis and work raises concerns about impairment and productivity. While some research suggests potential benefits, like pain management, further studies are needed to understand its impact on cognitive function and workplace safety. Establishing clear policies and guidelines is essential to navigate this complex issue effectively.

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Page last reviewed: September 29, 2021
Page last updated: September 29, 2021