The Centers for Disease Control and Prevention (CDC) published advice for businesses that employ drivers in states where marijuana is legal on how to mitigate the risk of impaired driving.
In its blog post, the CDC’s National Institute for Occupational Safety and Health (NIOSH) notes the dangers of driving under the influence of THC but recognizes the issue is complicated owing to varying state policies and the lack of a method or tool to accurately measure active THC impairment.
Unlike alcohol, THC can be detected in the body for weeks after use, so its presence in the body is not proof that the person is impaired at that moment.
The CDC recommends employers adopt marijuana policies in line with the “current laws in each state where your company operates,” which means adopting a “zero-tolerance policy for marijuana may not be possible, depending on your state’s laws.”
In New York, for instance, the Department of Labor updated its policy on workplace drug testing to prohibit employers from screening for THC following marijuana legalization in the state. The amended policy contains exceptions though, namely for workers employed by the federal Department of Transportation.
Amazon, one of the largest employers in the US, also recently scrapped its drug testing policy for workers, including for drivers.
If a zero-tolerance approach is prohibited by state law, the CDC recommends that employers should, at a minimum, prohibit employees from on-the-job marijuana use, or arriving at work under the influence of cannabis.
CDC also advises employers to seek out a cannabis attorney to “review your policy and provide feedback” before instituting any policy change.
The CDC then lays out certain parameters for THC screenings, should an employer carry them out. The workers should understand under what conditions they may be tested, a trained medical professional should interpret the test results, and workers should be informed that CBD products could contain traces of THC that may be detected in a drug test.
The CDC then advises employers to ensure “access to support for employees with drug problems, either through in-house programs or referrals to local resources” and to keep informed on “the relevant state marijuana laws and any improved methods for determining impairment.”
“Despite some unanswered questions about marijuana’s role in crash risk, workers under the influence of marijuana do not have the skills needed to drive safely,” the CDC concludes in its post. “Because marijuana use is on the rise for adults in the U.S., this substance needs to be addressed by all workplace motor vehicle safety programs.”
As the CDC indicates, the evidence on blood THC concentrations and active THC impairment is mixed.
A federally-funded study found no increased risk of a motor vehicle accident for drivers with two to five nanograms of THC per milliliter of blood – the typical legal THC limit under cannabis DUI laws– compared to drivers who had not used cannabis.
Similarly, an investigation by the Congressional Research Service in 2019 concluded that though “marijuana consumption can affect a person’s response times and motor performance… studies of the impact of marijuana consumption on a driver’s risk of being involved in a crash have produced conflicting results, with some studies finding little or no increased risk of a crash from marijuana usage.”
Incidentally, a comprehensive analysis of motor vehicle data over a 12 year period across six states found no association between adult-use cannabis legalization and an increase in the number of persons involved in a motor vehicle crash who then tested positive for THC.