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As with many laws in the United States, the regulations regarding the use of marijuana, both for recreational and medical purposes, are rapidly evolving.

The prohibition of cannabis began in the United States in 1911, when lawmakers in Massachusetts declared that a medical prescription was needed to purchase the drug. Many states quickly followed suit by imposing even stricter laws, banning the use of marijuana altogether and criminalizing the possession of it. The tide shifted, however, when California became the first state to legalize the use of medical marijuana in 1996. By 2016, that law expanded to include recreational use. 

As of April 2019, ten states have fully legalized the use of marijuana for both medical and recreational purposes.  Another 23 states have legalized the medical use of cannabis. And while 17 states still completely prohibit the drug, the legalization of marijuana is sweeping across the United States at a rapid pace. This presents a challenge for employers who want to maintain safety and efficiency at work.

As the use of cannabis is legalized and becomes accepted in society, employers and employees alike need to remember that similar to alcohol, marijuana can impair the user’s ability to react and perform basic tasks at work.  There are two compounds in a marijuana plant. The first is called cannabidiol, or CBD. This compound does not cause a feeling of euphoria but can treat several conditions, including:

  • Pain
    • Nausea
    • Seizures
    • Anxiety
    • Migraines
    • Depression

The second compound in a cannabis plant is called tetrahydrocannabinol, or TCH, which causes several side effects that may endanger the safety of a workplace. These side effects include:

  • Delayed reactions
    • Problems with coordination
    • Hallucinations
    • Accelerated heart rate
    • Memory loss

Under federal law, all forms of marijuana are still illegal. It’s classified as a Schedule 1 drug, which means the federal government considers it an addictive drug with no medical value. 

Employees working at businesses that receive federal grants, or those who need to operate a motor vehicle for work, such as employees of the Department of Transportation, should never use marijuana, even if it’s legal in that state or the employee is only using when not at work.

For safety and productivity, private employers can still take a zero-tolerance stance and require periodic drug testing or in the wake of an accident. Employers who require sobriety at work can treat marijuana as they would alcohol or other prescription drugs that cause impairment. This is true, even in states where marijuana has been legalized.  However, with cannabis laws changing rapidly, a zero-tolerance stance against marijuana where it is legal can open the door to potential problems for employers.

In states where medical marijuana is legal, not hiring a candidate based on a positive drug test can result in a discrimination lawsuit. This is due to the Americans with Disabilities Act. Similarly, once a person is hired, if the results of a workplace drug test are positive for marijuana, that employee may be protected from termination. 

This is all complicated by the fact that marijuana can stay in a person’s system for weeks after use. 

In fact, it is nearly impossible to determine if a positive test result means an employee is currently impaired or if it was legally used while the person was off-duty. This makes it essential that an employer and their management understand what constitutes reasonable suspicion.

Currently, a blood test can only detect TCH in a person’s system for 3 to 4 hours. Saliva tests detect marijuana for approximately 24 hours after use. Urine tests results can detect cannabis in the system 30 days after use. And a hair test, which offers the longest detection window, can detect traces in an employee’s system for up to 90 days.

Prescriptions for medical marijuana can affect employers in another way, through workers’ compensation laws and unemployment benefits.  


As the legalization of marijuana use expands to more states are passing bills regarding its use in the workplace, it’s critical for employers to stay up to date on new laws and how they affect the workplace.

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David Bell

After seeing firsthand the effects of employee drug use, David Bell worked his way into the industry and up to his current role as CEO of USA Mobile Drug Testing, so that he could help employers ensure a safer and more productive workplace. Today he writes extensively on compliance and speaks at industry events to help educate employers.

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