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How Much Pot Is Too Much?

So let’s say that about six weeks from now, Nevada voters say yes and legalize adult use of marijuana.

After that, Nevada will have to create regulations on how smoking and driving: how much pot someone can smoke before they are unable to drive.

Already, researchers are working on roadside tests to help police determine how much tetrahydrocannabinol or THC is in a driver’s system. THC is the psychoactive in marijuana responsible for the high.

Stanford University is working on a device called a potalyzer that will test saliva for THC.

The big question is: does THC in the blood determine whether someone is high?

An officer who has dealt with stoned drivers might be able to answer that.

James Green served 21 years with the Henderson Police Department, retired as a captain and now works in the medical marijuana business for dispensary NevadaPure.

Green told KNPR's State of Nevada that officers don't just look at what a person gets on a breathalyzer test to determine if he or she is impaired. 

"What we really do is look at the impairment of the driver," he said, "So what were the driving actions that caused them to have contact with law enforcement. Then once they're pulled over, everything from speech, their eyes, the odor of an alcoholic beverage or any other indication."

Green said that people can have THC in their system but not be impaired by it. 

Which is precisely the problem with Nevada's current law, according to Joe Brezney with the Coalition to Regulate Marijuana Like Alcohol.

He said the Nevada has the toughest marijuana DUI law in the country with a five nanongram cutoff for metabolized marijuana and two nanograms for active marijuana. He said it is much tougher than the national standard for driving a train. 

"Our own district attorney said we really need to make sure people are impaired because this arbitrary number is difficult both because it is so low; it is basically meant to be a trigger if anyone has any residual THC in their system," he said, "And because until recently there wasn't an affirmative defense for medical marijuana patients who usually walk around with more than five nanograms of that inactive metabolite in their system."

One of the most notable cases in this debate happened 16 years ago in Nevada. Jessica Williams was driving back to Las Vegas after partying with friends at Valley of Fire State Park

While driving home, Williams fell asleep, crashing her car into a group of teenagers picking up trash in the median of I-15 as part of a youth offenders work crew. Six teenagers were killed. 

However, because she still had THC in blood she was convicted of felony driving with a prohibited substance in her blood, despite her attorney's best efforts to show she was not impaired at the time. 

Green said there are no statistics in Nevada of the number of people arrested for THC impairment. 

"Statistically it is a very small number that really hasn't caught their attention that's why they don't really capture it," he said, "It's really the alcohol." 


James Green, former Henderson Police captain, Nevada Pure; Joe Brezny, spokesman, Coalition to Regulate Marijuana Like Alcohol

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Joe Schoenmann joined Nevada Public Radio in 2014. He works with a talented team of producers at State of Nevada who explore the casino industry, sports, politics, public health and everything in between.