THC Presence Versus Impairment

With the increase in marijuana legalization, employers, insurers, and law enforcement are faced with a conundrum.

September 24, 2015 Photo

When managing workers’ compensation or liability claims, impairment at the time of an accident is one of the most important factors to understand. Whether the accident was falling down stairs or crashing into a car, knowing to what extent the person was impaired—if at all—is one of the keys to identifying causality and defining responsibility.

Separate from distraction, which can be a momentary lack of focus, impairment can occur in a number of different ways, and it can be a reasonably permanent state. For example, some elderly drivers are not allowed on the road due to diminished cognitive abilities, reaction times, and physical capabilities. As the workforce ages, these kinds of concerns will increasingly be relevant.

However, the more vexing type of impairment is when individuals voluntarily create an altered state. Whether via alcohol, appropriate or nonmedical use of prescription drugs, or illegal drugs, workers who ingest chemicals that create impairment can dramatically increase the likelihood of accidents and injuries. Any substance that affects the ability to make good judgments; slows cognitive abilities; reduces the ability to concentrate or focus; affects depth perception, balance, or sense of time; or impacts the sense of risk can create dangerous situations for users and those around them.

The most problematic source of impairment of all is marijuana. Setting aside the complications of individual states legalizing recreational and medical use of the drug while it remains illegal at the federal level, the largest concern to both employers and employees is whether presence equals impairment. Because various chemical components of marijuana last longer in the body than many other chemicals, it is a unique quandary.

“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,” published online in April 2015 by the Journal of Occupational and Environmental Medicine (JOEM), is a must-read for every employer, clinician, risk manager, policymaker, and user. While the document is full of important details, one of the most important sections is entitled, “Metabolism and Impairment,” and includes useful facts, such as:

  • Common, self-described effects are relaxation, euphoria, relaxed inhibitions, sense of well-being, disorientation, altered time and space perception, giddiness, increased appetite, and a more vivid sense of taste, sight, smell, and hearing. Commonly observed central nervous system effects include lack of concentration, impaired learning and memory, alterations in thought formation and expression, drowsiness, and sedation. These psychological effects are accompanied by physiological manifestations of conjunctival injection, a significant increase in heart rate over baseline, dry mouth and throat, increased appetite, and vasodilatation.
  • For smoked marijuana, subjective impairment begins soon after smoking initiation, peaks in about one hour, and lasts three to four hours after smoking. Experimental studies suggest that measurable impairment in test subjects lasts approximately six hours. Impairment periods vary with the dose administered and the route of administration.
  • The subjective “high” after oral administration (i.e., edibles) usually occurs approximately 30 minutes after consumption. There is some evidence that with doses less than 18mg, impairment decreases to a level of normal performance around five hours post-ingestion. A smaller study of oral ingestion demonstrated impairment of driving skills up to 10 hours after ingestion of higher doses.
  • Impaired behavior from acute use differs between occasional users and long-term users. There is good evidence that chronic, frequent marijuana users exhibit less impairment from THC (tetrahydrocannabinol) than do occasional users.

This information makes it clear that impairment from marijuana is intense, short-lived, and can be difficult to separate from the mere presence of the drug. And therein lies the problem.

The complication—from both a pragmatic and legal standpoint—is the duration of time in which THC can be noted as present. Standard urine tests can detect traces of THC several days after use, according to In heavy marijuana users, however, urine tests can sometimes detect THC traces for weeks after use stops. According to “Marijuana Drug Test Detection Times,” an article viewed July 31, 2015, on the California NORML website, a single use of marijuana can be detected in a urine test from one to seven-plus days and in a blood test from 12 to 24 hours. Regular use of marijuana can be detected in a urine test from seven to 100 days and in a blood test from two to seven days. All of those are at least double the duration of amphetamines, cocaine, heroin or opiates, or PCP (phencyclidine).

However, the article stressed, “Note that urine tests do not detect the psychoactive component in marijuana, THC (delta-9-tetrahydrocannabinol), and therefore in no way measure impairment; rather, they detect the nonpsychoactive marijuana metabolite THC-COOH, which can linger in the body for days and weeks with no impairing effects.”

Obviously, there is dissonance between “presence” and “impairment,” and that makes action based on the results of a positive drug test difficult to ascertain.

There is growing evidence of being able to test for impairment through blood serum tests. According to the JOEM article, serum levels of an average of 3.8 (3.1 to 4.5) for oral and 3.8 (3.3 to 4.5) for smoked marijuana cause impairment approximately equivalent to a blood alcohol content (BAC) of around 0.05g percent. Additionally, the article states that the Joint Panel recommends a serum level of THC plus THC-OH of five ng/ml to determine impairment.

The correlation of THC levels to BAC, and a precise target for determining marijuana impairment, should be considered a breakthrough. However, blood tests may not be immediate, possibly making the results inconclusive regarding impairment at the actual time of the accident.

There currently are efforts to create a THC testing device that would work similarly to a Breathalyzer, which tests exhaled breath for blood alcohol levels. Washington State University and Cannabix Technologies are among many entities rushing to create this product. However, the technology is relatively nascent and reportedly can only validate presence (not impairment) and often only when marijuana was smoked within the past 30-120 minutes (not ingested via other means or after that time period). It remains to be seen whether these will be valuable tools for separating presence from impairment.

So at this point, employers, insurance companies, and law enforcement are left with this conundrum: Does presence equal impairment? Unfortunately, the answer is “it depends.” With the continued advancement of legalization efforts across the country, this issue will continue to have a greater impact on the ability to manage employees and claims. For now, those who need to ascertain impairment should do the following:

  • Use blood tests and serum level thresholds, along with sobriety tests like walking a straight line, quoting the alphabet, or observing pupil dilation as close to the accident/injury time as possible.
  • Clarify when the user last ingested marijuana and the delivery mechanism, within the limits allowed by corporate policy and state law.
  • Consult with counsel on implications of state laws for the use of marijuana and how positive test results impact human resource or claims adjudication decisions.
  • Identify compliance concerns with the Drug-Free Workplace Act, Americans with Disabilities Act, or other federal laws.
  • Remain engaged as the legal, statutory, and societal circumstances evolve.

Marijuana use—legal or illegal—and its impact on the workplace and claims adjudication is no longer an irrelevant academic issue. On this issue, upfront due diligence and strategic planning can mitigate potential future exposure.

About The Authors
Mark Pew

Mark Pew is senior vice president for PRIUM. He has been a CLM Fellow since 2011 and can be reached at

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