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Jo McGuire is the Executive Director of the National Drug and Alcohol Screening Association, which is the largest membership organization in the U.S. for those operating in the workplace drug testing space. She was appointed to serve on the Colorado Governor’s Task Force to regulate CO State Constitutional Amendment 64 due to her expertise in the drug testing industry and has participated in the United Nations General Assembly on the World Drug Agreements, the 68th Session of the Commission on Narcotic Drugs, and the first and second Latin American Congress on Workplace Drug Testing. Jo is a Certified Substance Abuse Program Administrator (CSAPA) with a B.S. in Sociology and a Minor in Cannabis Studies from Colorado State University-Pueblo. Jo serves as a board member for the Community Alliance for Drug Free Youth, Science Team and the Recovery Ready Workplace Institute’s Employment Council. She is a recognized subject matter expert and seasoned public policy advisor.
For any questions about NDASA and the work the association does, contact Jo at [email protected]. |
Welcome to the National Drug & Alcohol Screening Association (NDASA)!
NDASA is the voice of the nation’s drug and alcohol screening industry. Our diverse membership includes testing companies, employers, laboratories, Third Party Administrators, human resources managers, safety professionals, substance abuse counselors and others. We stand together to maintain drug-free workplaces and protect public safety.
To promote our industry’s interests, NDASA provides best-practices professional training and certification, hosts national and regional educational conferences, offers informational resources, leads governmental advocacy efforts on federal and state levels, and works closely with regulators who impact our industry, including the U.S. Department of Transportation.
As a 501C organization, NDASA is committed to serving our members in a professional and transparent manner and while we are governed by an elected Board of Directors, we are proud that our association is member driven and member owned.
The Why
NDASA was founded in 2018 as a public safety response to a growing need for training, advocacy and best-practice standards for the drug and alcohol testing industry. The data tells the story:
NDASA is the voice of the nation’s drug and alcohol screening industry. Our diverse membership includes testing companies, employers, laboratories, Third Party Administrators, human resources managers, safety professionals, substance abuse counselors and others. We stand together to maintain drug-free workplaces and protect public safety.
To promote our industry’s interests, NDASA provides best-practices professional training and certification, hosts national and regional educational conferences, offers informational resources, leads governmental advocacy efforts on federal and state levels, and works closely with regulators who impact our industry, including the U.S. Department of Transportation.
As a 501C organization, NDASA is committed to serving our members in a professional and transparent manner and while we are governed by an elected Board of Directors, we are proud that our association is member driven and member owned.
The Why
NDASA was founded in 2018 as a public safety response to a growing need for training, advocacy and best-practice standards for the drug and alcohol testing industry. The data tells the story:
- Employee substance use costs U.S. employers more than $164 billion annually and small-business owners face upwards of $7,000 per month in lost revenue due to employee turnover, absenteeism, lack of productivity, accidents, injuries, and even workplace fatalities.
- According to the U.S. Department of Justice 50 percent of workplace accidents and up to 40 percent of employee theft is caused by drug abuse.
- Nearly 70 percent of the estimated 22.4 million illicit drug users, ages 18 or older, are employed full or part time.
- Some 41.2 million binge drinkers are in the workplace.
- The rate of workforce drug positivity hit a 16-year high in 2019, according to Quest Diagnostics.
- Ongoing changes in drug legislation are making the development and enforcement of workplace drug policies, increasingly difficult. As of 2020, 33 states have legalized marijuana for medical use and 10 states and the District of Columbia for recreational use. Some states, including Oregon, are moving toward decriminalization of a host of other illicit substances.
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Marijuana and Safety-Sensitive Work
https://ndasa.com/2026/07/13/marijuana-and-safety-sensitive-work/
July 13, 2026 By NDASA
By Todd Simo, MD, President, American Association of Medical Review Officers; Melissa Snider-Adler, MD, Board Member of the Medical Review Officer Certification Council; and Patrice Kelly, JD, President, Patrice Kelly Consulting, LLC
Regulatory overview
In October 2022, President Biden asked the U.S. Department of Health and Human Services (HHS) and the Drug Enforcement Administration (DEA) to review how marijuana is scheduled under the Controlled Substances Act (CSA). In August 2023, HHS recommended to DEA that marijuana be moved from Schedule I to Schedule III, based on HHS’ scientific and medical evaluation. In May 2024, the DEA proposed a rule that, if finalized, would transfer marijuana to Schedule III.
Advocates on both sides of the issue (pro and con) expressed opinions during the rescheduling process. As a reflection of the strong public interest in marijuana rescheduling, the DEA received more than 42,000 public comments on its proposal and, in August 2024, the DEA announced that it would hold a hearing on it. Due to the change of administration, this process ground to a halt.
On Dec. 18, 2025, President Trump issued an executive order instructing the U.S. Attorney General to “take all necessary steps to complete the rulemaking process related to rescheduling marijuana to Schedule III of the CSA in the most expeditious manner in accordance with federal law.” On April 24, 2026, Acting Attorney General Todd Blanche issued an order immediately placing in Schedule III both FDA-approved products containing marijuana and marijuana products regulated by a state medical marijuana license, and provided for initiation of an expedited administrative hearing process to consider the broader rescheduling of marijuana from Schedule I to Schedule III to begin June 29, 2026. See AG Order No. 6754-2026 (April 23, 2026); published April 28, 2026, as a final rule at 91 Federal Register 22714 (April 28, 2026)
There are caveats within the Attorney General’s order that change the current dynamics of state medical marijuana programs.
Challenging the “Marijuana is safer than alcohol” narrative
The well-funded marijuana lobby has persuasively promoted its message that marijuana is safer than alcohol. This is a bit like playing “Two Lies and a Truth.”
There is no debate that alcohol is an impairing, addictive substance that can cause long-term health conditions and may shorten life expectancy. By the same logic, there should be no debate that marijuana is also an impairing, addictive substance that can cause long-term health conditions and may truncate life expectancy. Like all drugs, overuse/abuse causes the majority of problems. And, like all substances, overuse and misuse are where the majority of problems occur.
The Truth
More than 2,000 people die each year due to alcohol poisoning. When looking at the risk of fatal overdose, it is true that marijuana appears to be safer than alcohol. The active parts of marijuana, delta-9 tetrahydrocannabinol (THC) specifically, will not cause fatal respiratory depression in the same way opioids, alcohol, or benzodiazepines can. Cannabinoids primarily act on receptors called CB1 receptors, which are part of the endocannabinoid system (ECS) we all have in our bodies. These receptors are not strongly expressed in the brainstem’s respiratory rhythm generators, and they do not directly shut down the drive to breathe. This is one of the reasons we often hearpeople say you “cannot overdose” from marijuana use.
That statement, however, can be misleading.
While direct fatal THC overdose is rarely reported, people still can die from injuries, incidents, crashes and medical events related to the cognitive and psychomotor effects of cannabis. Those deaths may not be recorded as deaths “from marijuana,” even when cannabis-related impairment contributed to the event.
One such case of a medical event was found in a report of a 27-year-old male who died after ingesting 600 mg of THC edibles and smoking an unknown amount of marijuana. The autopsy listed anoxic brain injury following cardiac arrest, citing multi-route consumption.
The lies
When it comes to the duration of impairment after use and the ability to identify reliably when someone is under the influence, marijuana is far less predictable and, therefore, less safe than alcohol. When an individual consumes alcohol, intoxication and impairment are linked and occur simultaneously. When an individual uses marijuana, impairment often continues longer than the acute intoxication phase – leading the individual to think incorrectly that they are not impaired because they no longer feel intoxicated or “high.”
Lie #1: Pharmacology of THC (length of impairment)Alcohol is both intoxicating and impairing based upon a blood alcohol level achieved after drinking. The degree of impairment is based on the blood alcohol level because alcohol is distributed freely between the brain and blood. As the blood alcohol level diminishes, the intoxicating and impairing effects directly caused by alcohol also diminish. This means the intoxication/impairment window for alcohol is related directly to the blood alcohol level.
Marijuana intoxication (the “high”) is caused primarily by THC binding to brain receptors. The cannabis plant also contains other active chemical compounds, called cannabinoids, which act on the brain and body. There are more than 120 cannabinoids; most are not well studied and may contribute to both the intoxicating effects and ongoing impairment. Typically, the effects of THC intoxication are dependent on the dose of THC (both the potency and amount used), the route of administration, and other individual factors. The effects may include euphoria, relaxation, altered sensory perception, increased appetite, paranoia, increased anxiety, and/or restlessness. The effects usually peak 20-30 minutes after smoking begins, and last about 3-6 hours once discontinued. When using edibles, the intoxication timeframe is different. The onset of feeling “high” starts later, sometimes several hours after ingestion; however, the duration of the intoxication is also longer, often lasting 6-12 hours or longer.
Research indicates THC-induced impairment can remain significant, or even peak, while blood levels of THC are rapidly decreasing. Unlike alcohol, there is no direct, linear correlation between blood THC concentration and the level of impairment. Even when the person no longer feels “high,” THC sequestered in the brain continues to interact with the endocannabinoid system, causing impairment in higher brain function.
Impacts of THC
Impact on cognitive and motor functions of THC and the other components found in marijuana include:
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. It is important to acknowledge that these positive drug tests demonstrated marijuana, specifically delta-9 THC, exposure. They did not definitively prove impairment. However, the findings show an association between marijuana exposure within the detection window of the testing method and increased occupational injuries and accidents.
Further, research also has demonstrated a statistically significant association between marijuana use and increased risk of motor vehicle crashes. One such study from 2022, published in the Journal of Studies on Alcohol and Drugs, showed an analysis of five states that allow the recreational use of marijuana for adults aged 21 and older revealed a 5.8% increase in the rate of traffic crash injuries and a 4.1% increase in fatal crash rates after legalization and the onset of retail sales. The researchers found no increase at the same time in a comparison group of states that did not legalize the drug.
All of these points help explain why marijuana is not alcohol, and the length and type of impairment after marijuana use are of concern to employers. A person who uses marijuana the evening before work may not show obvious signs of intoxication or impairment the next day; however, they still may have impairment in higher brain functions, including executive function. That impairment may create risk for the employee, their co-workers, the public, and the workplace environment, particularly in safety-sensitive positions where the job requires the very brain functions that marijuana can affect: attention, judgment, reaction time, coordination, decision-making, and the ability to recognize and respond to hazards.
Lie #2: Ability to test for definitive impairment of marijuana useOne of the most persistent misconceptions is that we can test for marijuana impairment in the same way we test for alcohol impairment.
We cannot.
Unlike alcohol, where a blood alcohol concentration (BAC) provides a reliable and predictable relationship to impairment, there is currently no test that definitively determines impairment from marijuana or THC. In the workplace, we use drug testing as a risk mitigation tool. The primary purpose of drug testing is deterrence. However, as we know, drug testing is also an accurate detection tool. Drug testing identifies the use of a substance, in this case, marijuana, at a pre-determined level in a timeframe that is known to increase the risk of impairment. However, it is important to understand what a drug test can and cannot tell us.
What drug testing actually tells us
Drug testing detects the presence of a substance or its metabolites, not impairment. Different testing matrices answer different questions:
The science gap
The challenge of testing for impairment after the use of marijuana lies in the pharmacology of THC.
THC is a lipophilic substance, meaning it is stored in fat and brain tissue, released gradually over time, and its effects and duration can vary significantly between individuals. This is why blood THC levels can be decreasing while impairment is still present; individuals may no longer feel “high” but still can have cognitive impairment, and there is no consistent, linear relationship between THC levels and functional impairment.
As stated above, impairment can persist beyond intoxication with significant impacts on attention, reaction time, executive function, and decision-making, even when outward signs are minimal or absent.
Drug testing is not an impairment test. It is a risk-mitigation tool.
It helps answer questions like:
The real-world implication
Because we understand how THC and other cannabinoids affect the brain and how long those effects may last, we know impairment can occur within the same window of detection, and in some cases, beyond it.
Bottom line
The idea that we can definitively test for marijuana impairment is simply not supported by science. But that does not mean we are without tools.
It means we need to use the tools we have, including drug testing, observation, policy, and education, to manage risk effectively.
Additional Point: Medical Marijuana Use and Determination of Fitness for Duty
Safety concern with usage is not unique to marijuana. There are multiple classes of medications (opioids, benzodiazepines, etc.) that cause concerns, particularly when being used by employees performing safety-sensitive duties.
The safety concern raised by an employee’s use of these medications often can be resolved by determining the dose, timing, and frequency of use.
When prescribing a medication, the medical provider knows the exact dose of the medication along with the recommended usage pattern. For example, if a physician treating someone with generalized anxiety disorder prescribes for severe anxiety Valium at a dose of 5 mg once per day as needed, that physician has a certain confidence of how that patient used the medication when seen at the follow-up visit.
To further augment a provider’s ability to assure his/her patient’s controlled substance use, there are Prescription Drug Monitoring Programs (PDMPs) in place. The PDMPs are state-run, electronic databases that track the prescribing and dispensing of controlled substances (schedules II-V). PDMPs aim to reduce prescription drug misuse, addiction, and overdose by providing real-time data to clinicians and pharmacists to identify high-risk patients and “doctor shopping” behavior.
However, for medical marijuana programs, there are no such guardrails. The original intent of medical marijuana programs was for compassionate care. Medical marijuana was to be used solely when traditional prescription medications were not effective. A medical marijuana recommendation is based on state law, which allows that person to buy and possess a certain amount (typically by weight) of a marijuana product. There is no known dose of THC or other cannabinoids being used at any one time, nor is there any guardrail in place regarding frequency of use. As an illustration, compared to the Valium (also a DEA schedule III medication) prescription with a known dose and controlled amount, a medical marijuana recommendation holder in California can buy up to 8 ounces of dried flower (or plant conversion equivalent) and 12 immature plants per day.
Because cannabis can have a prolonged impairment window, and because the dose, amount used, timing, frequency of use, and amount of psychoactive cannabinoids consumed, including THC, often cannot be reliably confirmed, it is extremely difficult to resolve workplace safety concerns related to medical cannabis use.
Unlike many prescribed medications, medical cannabis does not allow for the same type of assessment of dose, timing, and frequency of use. As a result, the potential risk in a safety-sensitive workplace cannot be assessed or resolved with any level of confidence.
Conclusion
It is important to remember that the U.S. Department of Transportation’s drug testing regulations implemented in 1989 were a response to several tragedies that took place because of marijuana. Specifically, marijuana-related crashes took place in: January, 1987 (Amtrak and Conrail crash in Chase, Maryland) in which two Conrail operators tested positive for marijuana (16 fatalities and 170 injuries); February, 1987 (Metro North crash in New York) in which the engineer tested positive for marijuana (30 injuries); in 1988 (Bronx, NY Metro-North commuter train crash) in which the engineer and four transit employees tested positive for marijuana and other drugs (one fatality); in 1985 (Miami, FL collision of two trains) in which one operator tested positive for marijuana and other drugs (16 injuries). These incidents are cited in the Congressional Report for the Omnibus Transportation Employee Testing Act of 1991 (OTETA), Report of the Senate Committee on Commerce, Science and Transportation on S. 676, 102nd Congress, 1st Session, pages 5 – 6. Since the inception of DOT-regulated testing in 1989, which was affirmed by OTETA, the National Transportation Safety Board has not found a single commercial transportation accident to have been caused by marijuana.
DOT-regulated testing follows a zero-tolerance approach to marijuana use, relying on urine testing, which has a long detection window. This means marijuana use, even outside of work, may lead to a positive test at or above the cutoff levels provided in the DOT’s regulation, creating a strong deterrent effect. Employees subject to drug testing under DOT regulations are well aware of the requirement to abstain from the use of marijuana.
For more than three decades, since the inception of DOT-regulated drug testing, these protocols have effectively prevented marijuana-related fatalities in commercial transportation. Thus, the prevention resulting from DOT-regulated testing has created an outstanding record of safety that is at risk of being wholly undone by the rescheduling of marijuana.
In short, marijuana use by DOT-regulated, safety-sensitive employees operating in commercial transportation has been deterred in the industries subject to drug testing for marijuana. The same is true for non-DOT testing to the extent that states require or companies otherwise choose to create DOT-like programs. In other words, DOT-regulated drug testing for transportation safety-sensitive employees has long been integral to maintaining safety standards within the domestic transportation sector, protecting America’s traveling public, while non-regulated workplaces that have mirrored DOT policies have provided for employee safety.
It is important that we don’t forget the lessons of the past, or be destined to repeat them.
July 13, 2026 By NDASA
By Todd Simo, MD, President, American Association of Medical Review Officers; Melissa Snider-Adler, MD, Board Member of the Medical Review Officer Certification Council; and Patrice Kelly, JD, President, Patrice Kelly Consulting, LLC
Regulatory overview
In October 2022, President Biden asked the U.S. Department of Health and Human Services (HHS) and the Drug Enforcement Administration (DEA) to review how marijuana is scheduled under the Controlled Substances Act (CSA). In August 2023, HHS recommended to DEA that marijuana be moved from Schedule I to Schedule III, based on HHS’ scientific and medical evaluation. In May 2024, the DEA proposed a rule that, if finalized, would transfer marijuana to Schedule III.
Advocates on both sides of the issue (pro and con) expressed opinions during the rescheduling process. As a reflection of the strong public interest in marijuana rescheduling, the DEA received more than 42,000 public comments on its proposal and, in August 2024, the DEA announced that it would hold a hearing on it. Due to the change of administration, this process ground to a halt.
On Dec. 18, 2025, President Trump issued an executive order instructing the U.S. Attorney General to “take all necessary steps to complete the rulemaking process related to rescheduling marijuana to Schedule III of the CSA in the most expeditious manner in accordance with federal law.” On April 24, 2026, Acting Attorney General Todd Blanche issued an order immediately placing in Schedule III both FDA-approved products containing marijuana and marijuana products regulated by a state medical marijuana license, and provided for initiation of an expedited administrative hearing process to consider the broader rescheduling of marijuana from Schedule I to Schedule III to begin June 29, 2026. See AG Order No. 6754-2026 (April 23, 2026); published April 28, 2026, as a final rule at 91 Federal Register 22714 (April 28, 2026)
There are caveats within the Attorney General’s order that change the current dynamics of state medical marijuana programs.
- The state dispensaries must seek federal DEA registration as manufacturers, distributors, and/or dispensers.
- The regulation creates an expedited review process under which these state medical marijuana dispensaries can submit their existing state credentials as evidence of state-law authorization.
- This process will take at least 60 days to six months from the issuance of the final rule.
- During that time, the dispensaries can continue to operate under their state licenses.
- State-authorized medical marijuana user certifications (i.e., medical marijuana cards) must clearly identify the issuing practitioner along with their signature, the date of issuance, and the medical marijuana user’s name and address.
Challenging the “Marijuana is safer than alcohol” narrative
The well-funded marijuana lobby has persuasively promoted its message that marijuana is safer than alcohol. This is a bit like playing “Two Lies and a Truth.”
There is no debate that alcohol is an impairing, addictive substance that can cause long-term health conditions and may shorten life expectancy. By the same logic, there should be no debate that marijuana is also an impairing, addictive substance that can cause long-term health conditions and may truncate life expectancy. Like all drugs, overuse/abuse causes the majority of problems. And, like all substances, overuse and misuse are where the majority of problems occur.
The Truth
More than 2,000 people die each year due to alcohol poisoning. When looking at the risk of fatal overdose, it is true that marijuana appears to be safer than alcohol. The active parts of marijuana, delta-9 tetrahydrocannabinol (THC) specifically, will not cause fatal respiratory depression in the same way opioids, alcohol, or benzodiazepines can. Cannabinoids primarily act on receptors called CB1 receptors, which are part of the endocannabinoid system (ECS) we all have in our bodies. These receptors are not strongly expressed in the brainstem’s respiratory rhythm generators, and they do not directly shut down the drive to breathe. This is one of the reasons we often hearpeople say you “cannot overdose” from marijuana use.
That statement, however, can be misleading.
While direct fatal THC overdose is rarely reported, people still can die from injuries, incidents, crashes and medical events related to the cognitive and psychomotor effects of cannabis. Those deaths may not be recorded as deaths “from marijuana,” even when cannabis-related impairment contributed to the event.
One such case of a medical event was found in a report of a 27-year-old male who died after ingesting 600 mg of THC edibles and smoking an unknown amount of marijuana. The autopsy listed anoxic brain injury following cardiac arrest, citing multi-route consumption.
The lies
When it comes to the duration of impairment after use and the ability to identify reliably when someone is under the influence, marijuana is far less predictable and, therefore, less safe than alcohol. When an individual consumes alcohol, intoxication and impairment are linked and occur simultaneously. When an individual uses marijuana, impairment often continues longer than the acute intoxication phase – leading the individual to think incorrectly that they are not impaired because they no longer feel intoxicated or “high.”
Lie #1: Pharmacology of THC (length of impairment)Alcohol is both intoxicating and impairing based upon a blood alcohol level achieved after drinking. The degree of impairment is based on the blood alcohol level because alcohol is distributed freely between the brain and blood. As the blood alcohol level diminishes, the intoxicating and impairing effects directly caused by alcohol also diminish. This means the intoxication/impairment window for alcohol is related directly to the blood alcohol level.
Marijuana intoxication (the “high”) is caused primarily by THC binding to brain receptors. The cannabis plant also contains other active chemical compounds, called cannabinoids, which act on the brain and body. There are more than 120 cannabinoids; most are not well studied and may contribute to both the intoxicating effects and ongoing impairment. Typically, the effects of THC intoxication are dependent on the dose of THC (both the potency and amount used), the route of administration, and other individual factors. The effects may include euphoria, relaxation, altered sensory perception, increased appetite, paranoia, increased anxiety, and/or restlessness. The effects usually peak 20-30 minutes after smoking begins, and last about 3-6 hours once discontinued. When using edibles, the intoxication timeframe is different. The onset of feeling “high” starts later, sometimes several hours after ingestion; however, the duration of the intoxication is also longer, often lasting 6-12 hours or longer.
Research indicates THC-induced impairment can remain significant, or even peak, while blood levels of THC are rapidly decreasing. Unlike alcohol, there is no direct, linear correlation between blood THC concentration and the level of impairment. Even when the person no longer feels “high,” THC sequestered in the brain continues to interact with the endocannabinoid system, causing impairment in higher brain function.
Impacts of THC
Impact on cognitive and motor functions of THC and the other components found in marijuana include:
- Impaired decision-making and planning: persistent deficits in executive functions, such as planning, organizing, and problem-solving.
- Reduced coordination: impacts on the ability to operate heavy machinery, drive or stop vehicles, or perform tasks requiring high precision, due to slowed fine motor skills and impaired coordination. In all of these tasks, the ability to halt operation or divert operation when faced with an obstacle can be as important as the actual performance of the action. For example, the ability to perform a defensive operational move to avoid an impact or injury can be compromised.
- Memory and attention deficits: difficulties with short-term memory and concentration, which are crucial for maintaining safety protocols. This also affects the ability to maintain safe performance because the decision-making time may need to be split-second to avoid injury to an individual.
- Impaired spatial perception: spatial perception, depth perception, peripheral vision, and visuospatial working memory can all be impaired by altering brain activity and visual processing.
- Divided attention deficits: impairment of the ability to quickly split focus between multiple inputs, such as looking over your steering wheel and noticing a child running towards the road.
- dose of THC in the marijuana;
- route of administration (with impairment from oral ingestion lasting longer than smoked/vaporized cannabis);
- history of prior use of marijuana;
- frequency of prior use of marijuana;
- age of initiation of marijuana use;
- other medications co-administered, which impact the metabolism of the cannabinoids or add to the impairing effects; and
- the individual’s own metabolism
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. It is important to acknowledge that these positive drug tests demonstrated marijuana, specifically delta-9 THC, exposure. They did not definitively prove impairment. However, the findings show an association between marijuana exposure within the detection window of the testing method and increased occupational injuries and accidents.
Further, research also has demonstrated a statistically significant association between marijuana use and increased risk of motor vehicle crashes. One such study from 2022, published in the Journal of Studies on Alcohol and Drugs, showed an analysis of five states that allow the recreational use of marijuana for adults aged 21 and older revealed a 5.8% increase in the rate of traffic crash injuries and a 4.1% increase in fatal crash rates after legalization and the onset of retail sales. The researchers found no increase at the same time in a comparison group of states that did not legalize the drug.
All of these points help explain why marijuana is not alcohol, and the length and type of impairment after marijuana use are of concern to employers. A person who uses marijuana the evening before work may not show obvious signs of intoxication or impairment the next day; however, they still may have impairment in higher brain functions, including executive function. That impairment may create risk for the employee, their co-workers, the public, and the workplace environment, particularly in safety-sensitive positions where the job requires the very brain functions that marijuana can affect: attention, judgment, reaction time, coordination, decision-making, and the ability to recognize and respond to hazards.
Lie #2: Ability to test for definitive impairment of marijuana useOne of the most persistent misconceptions is that we can test for marijuana impairment in the same way we test for alcohol impairment.
We cannot.
Unlike alcohol, where a blood alcohol concentration (BAC) provides a reliable and predictable relationship to impairment, there is currently no test that definitively determines impairment from marijuana or THC. In the workplace, we use drug testing as a risk mitigation tool. The primary purpose of drug testing is deterrence. However, as we know, drug testing is also an accurate detection tool. Drug testing identifies the use of a substance, in this case, marijuana, at a pre-determined level in a timeframe that is known to increase the risk of impairment. However, it is important to understand what a drug test can and cannot tell us.
What drug testing actually tells us
Drug testing detects the presence of a substance or its metabolites, not impairment. Different testing matrices answer different questions:
- Urine testing detects past use, often days to weeks after consumption
- Oral fluid testing detects more recent use, typically within approximately 24 hours (longer in some individuals)
- Blood testing detects very recent exposure, but still does not correlate well with impairment and is not commonly used for workplace drug testing
- Hair testing reflects historical use over weeks to months
- Laboratory-based breath THC testing detects the presence of THC in breath and can be detected for up to 3-4 hours after marijuana use
The science gap
The challenge of testing for impairment after the use of marijuana lies in the pharmacology of THC.
THC is a lipophilic substance, meaning it is stored in fat and brain tissue, released gradually over time, and its effects and duration can vary significantly between individuals. This is why blood THC levels can be decreasing while impairment is still present; individuals may no longer feel “high” but still can have cognitive impairment, and there is no consistent, linear relationship between THC levels and functional impairment.
As stated above, impairment can persist beyond intoxication with significant impacts on attention, reaction time, executive function, and decision-making, even when outward signs are minimal or absent.
Drug testing is not an impairment test. It is a risk-mitigation tool.
It helps answer questions like:
- Has this person used a substance?
- Was that use recent?
- Does this result align with workplace policy?
The real-world implication
Because we understand how THC and other cannabinoids affect the brain and how long those effects may last, we know impairment can occur within the same window of detection, and in some cases, beyond it.
Bottom line
The idea that we can definitively test for marijuana impairment is simply not supported by science. But that does not mean we are without tools.
It means we need to use the tools we have, including drug testing, observation, policy, and education, to manage risk effectively.
Additional Point: Medical Marijuana Use and Determination of Fitness for Duty
Safety concern with usage is not unique to marijuana. There are multiple classes of medications (opioids, benzodiazepines, etc.) that cause concerns, particularly when being used by employees performing safety-sensitive duties.
The safety concern raised by an employee’s use of these medications often can be resolved by determining the dose, timing, and frequency of use.
When prescribing a medication, the medical provider knows the exact dose of the medication along with the recommended usage pattern. For example, if a physician treating someone with generalized anxiety disorder prescribes for severe anxiety Valium at a dose of 5 mg once per day as needed, that physician has a certain confidence of how that patient used the medication when seen at the follow-up visit.
To further augment a provider’s ability to assure his/her patient’s controlled substance use, there are Prescription Drug Monitoring Programs (PDMPs) in place. The PDMPs are state-run, electronic databases that track the prescribing and dispensing of controlled substances (schedules II-V). PDMPs aim to reduce prescription drug misuse, addiction, and overdose by providing real-time data to clinicians and pharmacists to identify high-risk patients and “doctor shopping” behavior.
However, for medical marijuana programs, there are no such guardrails. The original intent of medical marijuana programs was for compassionate care. Medical marijuana was to be used solely when traditional prescription medications were not effective. A medical marijuana recommendation is based on state law, which allows that person to buy and possess a certain amount (typically by weight) of a marijuana product. There is no known dose of THC or other cannabinoids being used at any one time, nor is there any guardrail in place regarding frequency of use. As an illustration, compared to the Valium (also a DEA schedule III medication) prescription with a known dose and controlled amount, a medical marijuana recommendation holder in California can buy up to 8 ounces of dried flower (or plant conversion equivalent) and 12 immature plants per day.
Because cannabis can have a prolonged impairment window, and because the dose, amount used, timing, frequency of use, and amount of psychoactive cannabinoids consumed, including THC, often cannot be reliably confirmed, it is extremely difficult to resolve workplace safety concerns related to medical cannabis use.
Unlike many prescribed medications, medical cannabis does not allow for the same type of assessment of dose, timing, and frequency of use. As a result, the potential risk in a safety-sensitive workplace cannot be assessed or resolved with any level of confidence.
Conclusion
It is important to remember that the U.S. Department of Transportation’s drug testing regulations implemented in 1989 were a response to several tragedies that took place because of marijuana. Specifically, marijuana-related crashes took place in: January, 1987 (Amtrak and Conrail crash in Chase, Maryland) in which two Conrail operators tested positive for marijuana (16 fatalities and 170 injuries); February, 1987 (Metro North crash in New York) in which the engineer tested positive for marijuana (30 injuries); in 1988 (Bronx, NY Metro-North commuter train crash) in which the engineer and four transit employees tested positive for marijuana and other drugs (one fatality); in 1985 (Miami, FL collision of two trains) in which one operator tested positive for marijuana and other drugs (16 injuries). These incidents are cited in the Congressional Report for the Omnibus Transportation Employee Testing Act of 1991 (OTETA), Report of the Senate Committee on Commerce, Science and Transportation on S. 676, 102nd Congress, 1st Session, pages 5 – 6. Since the inception of DOT-regulated testing in 1989, which was affirmed by OTETA, the National Transportation Safety Board has not found a single commercial transportation accident to have been caused by marijuana.
DOT-regulated testing follows a zero-tolerance approach to marijuana use, relying on urine testing, which has a long detection window. This means marijuana use, even outside of work, may lead to a positive test at or above the cutoff levels provided in the DOT’s regulation, creating a strong deterrent effect. Employees subject to drug testing under DOT regulations are well aware of the requirement to abstain from the use of marijuana.
For more than three decades, since the inception of DOT-regulated drug testing, these protocols have effectively prevented marijuana-related fatalities in commercial transportation. Thus, the prevention resulting from DOT-regulated testing has created an outstanding record of safety that is at risk of being wholly undone by the rescheduling of marijuana.
In short, marijuana use by DOT-regulated, safety-sensitive employees operating in commercial transportation has been deterred in the industries subject to drug testing for marijuana. The same is true for non-DOT testing to the extent that states require or companies otherwise choose to create DOT-like programs. In other words, DOT-regulated drug testing for transportation safety-sensitive employees has long been integral to maintaining safety standards within the domestic transportation sector, protecting America’s traveling public, while non-regulated workplaces that have mirrored DOT policies have provided for employee safety.
It is important that we don’t forget the lessons of the past, or be destined to repeat them.