Should California impose a THC limit on drivers? A state lawmaker says no

California drivers know the drill: 0.08 blood alcohol concentration is the legal limit for driving.

But what about marijuana? Should the state implement a blood test to determine if someone is impaired by THC, the key psychoactive ingredient in marijuana?

This is one of the questions that emerged after Californians voted to legalize recreational marijuana in 2016, with legal sales starting in 2018.

One state lawmaker, a former California Highway Patrol officer, is cautioning against that approach, arguing that THC blood content is not a reliable indicator of impairment.

Assemblyman Tom Lackey, R-Palmdale, said in an interview with The Sacramento Bee that so-called “per se” limits — like blood alcohol concentration — don’t make sense for cannabis users.

“It’s a very unique substance,” Lackey said, adding that marijuana is unlike alcohol when it comes to impairment.

Several states have established a “per se” limit for THC in the blood, including Colorado, Montana, Nevada, Ohio, Pennsylvania and Washington, though there is no consensus on what the limit should be, according to a report from the law firm Caldwell Everson shared by the federal Substance Abuse and Mental Health Services Administration.

One state, New Mexico, is currently considering a bill that would establish a limit as well.

Annie Kitch, a senior policy specialist with the National Conference of State Legislatures, told The Bee that testing for drug impairment is challenging due to the lack of an established relationship between the concentration of a drug such as THC and the level of impairment it causes in an individual.

“Additionally, drivers who may be under the influence of both drugs and alcohol are often cited for an over-the-limit blood alcohol concentration and rarely tested for other substances. As a result, data on drug-impaired driving is inconsistent and may not measure the full scope of the problem. To remedy these issues, states and law enforcement agencies are exploring new testing methods such as the use of oral fluids to detect drugs,” she said.

Lackey cited a two-year UC San Diego School of Medicine study that evaluated the simulated driving of 191 regular cannabis users after they consumed cannabis with varying levels of THC content.

The study, published in a recent issue of the “JAMA Psychiatry,” found that while THC consumption led to diminished driving ability, there was no relationship between post-smoking blood THC concentrations and driving simulator performance.

“The complete lack of correlation between blood concentrations and driving performance was somewhat surprising. It’s strong evidence against developing ‘per se’ driving under the influence statutes,” said study co-author Robert Fitzgerald in a statement.

Lackey noted that the UC San Diego study was representative of both regular and part-time cannabis users.

The Republican assemblyman has emerged as a vocal proponent of the legal cannabis industry. He said he wants to make sure “that our statutes don’t punish usage, that they punish impairment.”

Lackey said that it is too soon for lawmakers to consider legislation regulating marijuana-impaired driving.

“We need more studies and we need to wrap our head around this better,” he said.

Lackey said he would advocate for more cannabis research funding in the state’s 2022-23 budget, which lawmakers and Gov. Gavin Newsom are currently hammering out.

“That’s going to be our next move to try to get more funding,” Lackey said. “This study gave us some very powerful information to make sure we don’t go the wrong direction.”

This story was originally published February 24, 2022 at 9:41 AM.