Marijuana on the Jobsite: A Positive Test vs. Impairment


According to the U.S. Centers for Disease Control and Prevention, marijuana — or cannabis — is the most commonly-used federally illegal drug in the United States, with an estimated 48.2 million people using it in 2019.

Despite its recreational legalization in many states, employers are free to ban the use and possession of marijuana in the workplace and are not prohibited from disciplinary action against employees who are using marijuana during work hours or while using employer property. Moreover, an employer is not prohibited from taking employment action against an employee if the employee is impaired by cannabis while working.

How do I know if someone is impaired?

There currently is no legally or medically accepted definition of what constitutes “impairment” (or being “under the influence” of marijuana). Unlike alcohol testing, impairment by marijuana cannot be objectively measured by any scientifically proven methodology. Current testing does not identify intoxication, only the presence of marijuana metabolites or THC, the psychoactive ingredient in marijuana. There is also no dispositive and complete list of symptoms of impairment.

In some states employers may consider an employee to be impaired or under the influence of cannabis if the employer has a good faith belief that an employee manifests specific, articulable symptoms while working that decrease or lessen the employee’s performance or interfere with an employer’s obligation to provide a safe and healthy workplace, free from recognized hazards, as required by state and federal occupational safety and health laws. Signs of impairment while working (or on call) include, but are not limited to:

  • Changes in speech and demeanor
  • Impaired dexterity, agility and coordination
  • Irrational or unusual behavior
  • Negligence or carelessness when operating equipment or machinery
  • Disregard for the safety of the employee or others
  • Carelessness that results in any injury to the employee or to others
  • Involvement in any accident that results in serious damage to equipment or property

Only symptoms that provide objectively observable indications that the employee’s performance of the essential duties or tasks of their position are decreased or lessened may be cited and these symptoms do not provide definitive proof. Employers are cautioned that such symptoms may also be an indication that an employee has a disability protected by state or federal law.

Proof may require demonstrating one or more of the symptoms of being impaired by marijuana and testing positive for the presence of marijuana in the employee’s system at the time the symptom is demonstrated. While it may be possible to act without the confirmation of a positive test result, it has been suggested that it is risky to do so because the law also provides that the employee must be given “a reasonable opportunity to contest the basis of the determination.”

What cannot be cited by an employer as articulable symptoms of impairment?

Employers may not use drug testing as a basis for an articulable symptom of impairment. It is a widely recognized view that a marijuana-positive result by itself says virtually nothing about impairment at work. Marijuana can be detected in bodily fluids for up to 30 days and in hair for up to 90 days after use, long after the impairment effects have worn off (see National Institutes of Health: NCBI: Objective Testing: Urine and Other Drug Tests).

A best practice for employers who test current employees for marijuana is to define and explain “impairment” and being “under the influence.” They should establish a strong record of impairment independent of a marijuana-positive result. That would include thorough, contemporaneous documentation of the reasons employees are sent for a reasonable suspicion testing. It could include an accident investigation report that rules out non-drug-related causes where circumstances warrant that conclusion.

Employers are advised to consult outside counsel for help in revising policies and addressing new marijuana challenges in the workplace.

For more information on marijuana and its implications for the workplace visit the NAHB Construction Liability Resources page.

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