Now is not the time for a specific, misguided and scientifically dubious standalone law on marijuana DUI. (Courtesy photo)

Now is not the time for a specific, misguided and scientifically dubious standalone law on marijuana DUI. (Courtesy photo)

Get science right before implementing different DUI law for marijuana

Even as California and other states consider expanding the legal availability of marijuana for recreational as well as medicinal use, there has been a concerted push by some to create new laws criminalizing driving under the influence of marijuana’s active ingredient, THC.

But those marijuana-specific proposals, while intended to prevent dangerous driving, are flawed and not ready for prime time. That is because the science isn’t there yet to distinguish between drugged driving versus residual trace amounts of THC in the system. We already have provisions to protect the public from dangerous drivers of all kinds. We need to let the science catch up before we start making potentially problematic new laws.

The proposed laws attempt to set a “bright line” maximum level of THC in the bloodstream, similar to the 0.08 percent level for an alcohol-related DUI. In other words, the laws would make it a crime to drive with a particular amount of THC in the system, usually measured as nanograms per milliliter of blood.

Without getting too far into the biological details, the body processes marijuana very differently from alcohol, which metabolizes out of the system within a few hours of ingestion. THC, by contrast, can be detected for as much as a month after being ingested, long after it might impact motor skills.

So the first problem from a legal standpoint is that current tests can’t tell when someone ingested the marijuana, given that it could have been weeks earlier, long after any discernable impact on a driver’s abilities. The body continues to show signs of metabolizing THC long after it can have any impact on driving.

As well, it matters how you ingest the marijuana who is doing the ingesting, given the wide differences in the way individuals process THC. The blood, saliva and urine tests now available can only measure the then-current THC levels, which are not a reliable indicator of actual driver impairment.

Bright-line tests also have their problems even in alcohol DUI cases. Different people, in different settings are affected by alcohol in wildly differing ways. Under case law, defendants can legally claim they weren’t impaired because of the way their body handles alcohol. These issues multiply many times when applied to marijuana and driving.

Even more problematically, hard science still hasn’t been able to resolve these complications with actual, consistently replicable studies. University of California, San Diego researchers are undertaking ambitious tests to try to answer some of the many questions posed here, but it will be quite some time before that work is done.

Just as importantly, in California we already have a state law regulating driving while impaired by intoxicating substances other than alcohol. That law controls not just marijuana but drivers affected by prescription drugs such as opiate-based painkillers and even sleep aids such as Ambien, where swerving by drivers has been reported happening even the morning after taking a pill.

So the question is, why create a separate marijuana-specific DUI bill? I suspect it’s driven by many of the same forces that generally oppose any legalized use of marijuana, and certainly recreational use, as California’s Proposition 64 would allow if approved Nov. 8. But creating a standalone marijuana DUI law now would serve little good purpose, while creating unfortunate new problems.

It would potentially criminalize, again, marijuana use in situations where drivers aren’t actually impaired. It could unfairly affect even those who need marijuana for medical conditions, while providing little additional protection from dangerous drivers. And such laws would create a bright-line test before we even have definitive research that could scientifically draw that bright line.

Now is not the time for a specific, misguided and scientifically dubious standalone law on marijuana DUI.

Michael Chernis is a Los Angeles-based attorney specializing in the cannabis industry. As a founder of the LA Cannabis Task Force, he has lobbied on behalf of dispensaries to have more open laws surrounding medical marijuana.

If you find our journalism valuable and relevant, please consider joining our Examiner membership program.
Find out more at

Just Posted

Police Chief Bill Scott on Wednesday said a rebranding and reoganization of the former Gang Task Force amounts to “more than just the name change.” (Kevin N. Hume/S.F. Examiner)
Faced with surge in shootings, Chief Scott reenvisions SFPD’s Gang Task Force

New Community Violence Reduction Team adds officers with community-policing experience

Stores including Walgreens and Safeway are required to pay their employees additional hazard pay under a city ordinance that is currently set to expire later this month. (Shutterstock)
Grocery workers could gain additional weeks of $5 per hour hazard pay

San Francisco will vote next week on whether to extend a law… Continue reading

The fatal shooting of San Francisco resident Roger Allen by Daly City police on April 7 prompted protests in both cities. (Jordi Molina/ Special to the S.F. Examiner)
Daly City approves body-worn and vehicle cameras for police after fatal shooting

Daly City officials on Wednesday approved body and vehicle cameras for police… Continue reading

Baseball Hall of Famer Willie Mays attends an event to honor the San Francisco Giants' 2014 World Series victory on Thursday, June 4, 2015, in Washington, D.C. (Olivier Douliery/Abaca Press/TNS)
Willie Mays turns 90: San Francisco celebrates the greatest Giant

By Al Saracevic Examiner staff writer I couldn’t believe it. Willie Mays… Continue reading

Ja’Mari Oliver, center, 11, a fifth grader at Harvey Milk Civil Rights Academy, is surrounded by his classmates at a protest outside the Safeway at Church and Market streets on Wednesday, May 5, 2021 in support of him following an April 26 incident where he was falsely accused by an employee of stealing. (Kevin N. Hume/S.F. Examiner)
School community rallies behind Black classmate stopped at Safeway

‘When you mess with one of us, you mess with all of us’

Most Read