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Scientists Still Seek A Reliable DUI Test For Marijuana

Jul 30, 2017
Originally published on August 6, 2017 2:46 pm

This spring, 16 state patrol officers from Colorado and Wyoming took a couple days off their usual work schedule to do something special. They assembled in a hotel conference room in Denver. As instructed, they wore street clothes for their first assignment: going shopping at nearby marijuana dispensaries.

"It's a brave new world," said instructor Chris Halsor, referring to the years since Colorado legalized recreational marijuana.

There are now more marijuana dispensaries in Colorado than there are Starbucks shops, said Halsor, a Denver lawyer and former prosecutor. And though consuming cannabis is legal across the state, driving under its influence is not.

The cops in that conference room, with their buzz cuts and Mountain Dew, are all part of the force charged with keeping the roads safe. But first, they needed a formal pot education — to learn how to identify various marijuana products and paraphernalia when they pull over a driver they suspect is under the influence.

Here's the rub: Despite the increasingly legal use of cannabis in many states, cops still don't have the equivalent of a reliable alcohol breathalyzer or blood test — a chemically based way of estimating what the drug is doing in the brain. Though a blood test exists that can detect some of marijuana's components, there is no widely accepted, standardized amount in the breath or blood that gives police or courts or anyone else a good sense of who is impaired.

A number of scientists nationally are working hard to create just such a chemical test and standard — something to replace the behavioral indicators that cops have to base their judgments on now.

"We like to know the human error and the limitations of the human opinion," said Tara Lovestead, a chemical engineer at the National Institute of Standards and Technology in Boulder, Colo., who is working on setting standards for what a marijuana detection test might require.

It's actually really hard for Lovestead to do this kind of research because she works in a federal lab; federally, cannabis is considered a Schedule 1 substance, "a drug with no currently accepted medical use and a high potential for abuse." So even though Lovestead is in Colorado, getting hold of a sample for research purposes is just as hard as getting hold of heroin.

"We cannot use the stuff down the street," she said.

Aside from being a bureaucratic mess, coming up with a standardized blood or breath test is also a really tricky chemistry problem because of the properties of the main psychoactive chemical in cannabis: delta-9-tetrahydrocannabinol, or THC.

In states like Colorado, there is a THC blood test that law enforcement can use to show "presumed" impairment. If a person has more than 5 nanograms of delta-9-THC per milliliter of blood, a court or jury can infer that they are impaired, according to Colorado law (this is called "permissible inference" in legalese).

But Lovestead and others maintain that, scientifically speaking, that cutoff doesn't actually mean anything.

"We just don't know whether or not that means they're still intoxicated, or impaired or not," she said. "There's no quantitative measure that could stand up in a court of law."

Turns out it can be a lot harder to chemically determine from a blood or breath test that someone is high than to determine from such a test that they're drunk.

Ethanol, the chemical in alcoholic drinks that dulls thinking and reflexes is small and dissolves in water. Because humans are mostly water, it gets distributed fairly quickly and easily throughout the body and is usually cleared within a matter of hours. But THC, the main chemical in cannabis that produces some of the same symptoms, dissolves in fat. That means the length of time it lingers in the body can differ from person to person even more than alcohol — influenced by things like gender, amount of body fat, frequency of use, and the method and type of cannabis product consumed.

In one study, researchers had 30 frequent marijuana users stay at a research facility for a month without any access to drugs of any sort and repeatedly tested their blood for evidence of cannabis.

"And it shocked everyone, including ourselves, that we could measure, in some of these individuals, THC in the blood for 30 days," says Marilyn Huestis, a toxicologist with the University of Maryland School of Medicine who recently retired from leading a lab at the National Institute on Drug Abuse.

The participants' bodies had built up stores of THC that were continuing to slowly leech out, even though they had abstained from using marijuana for a full month. In some of those who regularly smoked large amounts of pot, researchers could measure blood THC above the 5-nanogram level for several days after they had stopped smoking.

Conversely, another study showed that people who weren't regular consumers could smoke a joint right in front of researchers and yet show no evidence of cannabis in their blood.

So, in addition to being invasive and cumbersome, the blood test can be misleading and a poor indicator of whatever is happening in the brain.

Recently, some scientists have turned their attention to breath, in hopes of creating something useful.

A number of companies, like Cannabix Technologies and Hound Labs, are in the process of developing breath detection devices. Tara Lovestead is providing the data that will help relate the concentration of THC detected in the breath to what's in the blood. Even though blood provides an incomplete and indirect inkling of what's happening in the brain, it's the measure law enforcement turns to as a benchmark.

That, too, is a chemist's nightmare. THC and other cannabinoids — the chemicals that cause a high — are really squirrelly. They degrade quickly and appear only in very tiny amounts in the breath.

Luckily, Lovestead's specialty is detecting tiny amounts of chemicals in the air. She and her colleagues have worked on methods to use tiny air samples to detect evidence of arson, buried bodies and hidden explosives. Marijuana is the next challenge.

In the future, she said, an accurate breath test would likely involve looking at a lot more than just THC — probably a whole combination of chemicals.

"One thing to look for would be metabolites — something that comes out of the breath that shows it actually went through your system," she said. Such a test would greatly reduce the possibility that someone might test positive from inhaling secondhand smoke, she said.

In the meantime, it's up to law enforcement officers like the ones in Chris Halsor's class to make the call, based on circumstantial evidence and their best guess.

"The whole point of this class is to get the officers to make correct decisions," said Halsor.

Many officers in his courses have never used marijuana — or haven't since some exploratory puffs in high school. These officers need training, he said, to boost their confidence — "confidence that they're making the right arrest decision and confidence that they're letting people go who really aren't impaired."

The cops attending his seminar in the spring paged through Dope Magazine, chuckled at a photo of an edible called "reef jerky" and watched a video together on how to dab — heating concentrated marijuana and inhaling the vapors. In their visit to a local marijuana dispensary, they examined gold-plated blunts — hollowed-out cigars filled with marijuana.

But the real test of these officers' ability to identify the signs of cannabis impairment faced them outside the hotel, in a parked RV that was plastered with bumper stickers.

Four volunteers for the project were inside the RV, legally getting as high as they wanted to, from a big plastic tub full of pot products.

"Good music, good company, good weed. It all goes together," said Eugene Butler, one of the four volunteers.

Butler and the three others had never met before. They had volunteered to get high and then interact with cops to help the officers learn the signs of cannabis impairment.

"We're going to willfully smell like pot around a bunch of cops," said Sharica Clark, laughing.

Inside the hotel, the officers practiced roadside sobriety tests on the four volunteers — determining each time if, in real life, they would have arrested these people for a DUI.

All the volunteers had smoked a lot of pot inside the RV. But in the sobriety tests, they performed differently.

A volunteer named Christine, for example, did well on math, quickly calculating how many quarters are in $1.75. But she didn't do well on other things, like balancing, remembering instructions and estimating time. (She was concerned about recrimination at work, and NPR agreed to use only her first name).

Christine, the officers all decided, would be a danger behind the wheel. In real life, they would have arrested her.

"Yeah, she'd be going to jail," said Rich Armstrong, an officer with Colorado State Patrol.

But things weren't so clear with the other volunteers. A lot of the officers had decided they wouldn't arrest Eugene Butler or a volunteer named John (who also asked that we not use his last name); both men aced the same roadside tests Christine flunked, even though they, too, had just smoked a lot in the RV.

And when it came to Sharica Clark, the officers decided it was essentially a toss-up as to whether they would have arrested her, based on her performance on the roadside tests. Yes, her pupils were huge, and she had a tough time touching her finger to the tip of her nose while her eyes were closed. But her balance, counting and recitation of the alphabet were, as Colorado State Patrol Officer Philip Gurley put it, "spot on."

"It was a tough one," said Tom Davis, another officer with Colorado State Patrol.

Right now, these officer's opinions loom large. If they decide you're driving high, you're going to jail. But at the end of the day, they're just making educated guesses. Two different officers could watch the same person doing the same sobriety test and make different decisions on whether to arrest. In previous courses, officers had decided that a volunteer was impaired when in fact the volunteer hadn't smoked at all.

So, just like the THC blood test, the judgments officers make can also yield false positives and negatives.

"This is one of those subjective areas," said Armstrong.

"It's too subjective," said Lovestead.

She recently published a paper in the journal Forensic Chemistry where she found the vapor pressure of THC — one of its fundamental physical properties. Lovestead believes finding and standardizing that measurement is a small but significant step toward a more objective route for evaluating intoxicated drivers.

In the meantime, courses like Halsor's are the best resource for officers. And at least now the class participants know what pot strains like Skunk Dawg, Hippie Chicken and Chunky Diesel actually smell like.

"Yeah," said Gurley. "It smells like the bottom side of a rock."

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

STACEY VANEK SMITH, HOST:

Marijuana is now legal in almost 30 states. But even in those states, it is still illegal to drive while impaired by the drug. But as NPR's Rae Ellen Bichell reports, that's left law enforcement and scientists struggling to find better ways to figure out who is impaired.

RAE ELLEN BICHELL, BYLINE: This spring, 16 state patrol officers packed into a hotel conference room in Denver. After an introduction and some slides, their instructor cued a YouTube video - How To Smoke.

(SOUNDBITE OF VIDEO)

BOBBY BLACK: Hi. I'm Bobby Black, senior editor of High Times Magazine. And today, we're going to show you how to do a dab.

BICHELL: The cops, with their buzz cuts and Mountain Dews, looked curious. Some took notes. After all, they were there for a proper education about weed.

(SOUNDBITE OF VIDEO)

BLACK: A bowl of water and some tongs if you're seasoning a new nail. And, of course, some shatter or wax.

SMITH: Chris Halsor started this class a few years ago, when Colorado legalize recreational marijuana.

CHRIS HALSOR: The whole point of this class is to get the officers to make correct decisions.

BICHELL: In this state and others, it's legal to be high, but it's illegal to drive while high. Right now, there's no breathalyzer that's proven to work. So it's up to officers like the ones in this room to make the call on whether someone they've pulled over has been driving impaired or not and, therefore, if they should be arrested. But a lot of them haven't been high themselves since some exploratory puffs in high school. They're lacking, Halsor says, in confidence.

HALSOR: Confidence that they're making the right arrest decision and confident that they're letting people go who really aren't impaired.

BICHELL: The students paged through DOPE Magazine, chuckled at a photo of an edible called reef jerky and ogled gold-plated blunts at a nearby dispensary. But the real test was sitting in the hotel parking lot in an RV plastered with bumper stickers.

EUGENE BUTLER: Yes. Good music, good company, good weed. It all goes together.

SHARICA CLARK: That's true.

BICHELL: The four volunteers - John, Christine, Sharica Clark and Eugene Butler - had never met before, but they shared a passion for pot, especially the free kind.

CHRISTINE: You've got some kief there, too?

BUTLER: But check this out. If you guys ever want to boost your high...

BICHELL: Just to be clear, it's legal to smoke pot on private property in Colorado, so they weren't doing anything wrong. These people, including Sharica Clark, were getting high as a kite for the greater good.

CLARK: We're going to willfully smell like pot around a bunch of cops (laughter).

BICHELL: The volunteers walk into the hotel, where the officers were waiting to practice sobriety tests on them. One group started with a volunteer named Christine. She didn't want to share her last name.

A.J. TARANTINO: Have you consumed any cannabis today?

CHRISTINE: Oh, yeah.

BICHELL: A.J. Tarantino, a trooper with Colorado State Patrol, took the lead with his colleagues Philip Gurley, Tom Davis and Rich Armstrong observing.

TARANTINO: Would you be willing to do voluntary roadside maneuvers?

CHRISTINE: Of course.

BICHELL: Christine did really well in math, but she didn't do well on other things like balancing, remembering instructions and estimating time.

PHILIP GURLEY: She showed multiple signs of impairment.

TOM DAVIS: Yeah, she'd be going to jail.

RICH ARMSTRONG: Or, yeah, she'd be arrested.

BICHELL: But then, the group moved on to Sharica Clark.

TARANTINO: Let's get situated here.

BICHELL: And things got a little more complicated. Yes, her pupils were huge, and Philip Gurley told her she had a tough time touching her finger to the tip of her nose while her eyes were closed.

GURLEY: But your balance, your counting, your alphabet - all spot on.

BICHELL: So in real life, would they have arrested her for driving impaired?

GURLEY: Yes.

ARMSTRONG: Boy, you're tough. I don't know if I would've or not, to be honest with you.

BICHELL: Right now, these officers' opinions loom large. If they decide you're driving high, you're going to jail. But they are just opinions.

TARA LOVESTEAD: It's too subjective.

BICHELL: Tara Lovestead is a chemical engineer at the National Institute of Standards and Technology in Boulder, Colo. She and her colleagues are looking for the chemical signature of a high, so that instead of relying on people to determine cannabis impairment, a standardized test might, one day, do the trick.

LOVESTEAD: We like to know the human error and the limitations of the human opinion and want to make it as scientific-based in fact as we can.

BICHELL: It's actually really hard to do this kind of research because Lovestead works in a federal lab and, federally, cannabis is considered a Schedule 1 substance. So even though she's in Colorado, getting a hold of a sample of THC for research purposes is just as hard as getting a hold of heroin.

LOVESTEAD: Right. We cannot use the stuff down the street (laughter).

BICHELL: It's also a really tricky chemistry problem. And that's because of the main chemical in cannabis that gets a person high, THC. In states like Colorado, there is a THC blood test, which can show, quote, "presumed impairment." But Lovestead and others maintain that, scientifically speaking, the test isn't reliable.

LOVESTEAD: We just don't know whether or not that means they're still intoxicated or impaired or not.

BICHELL: A leading research group found evidence of THC in the blood of frequent smokers up to a month after they stopped consuming. And, in other people, blood samples showed no trace of THC, even though the researchers had just watched them smoke joints.

LOVESTEAD: There's no quantitative measure that could stand up in a court of law.

BICHELL: Now, people like Lovestead are setting the standards for a reliable breath test starting with the fundamental physical properties of THC. But, in the meantime, back at the hotel, this course is the best there is. And, at least, now, the officers know what pot strains like OG Kush and Skunk Dawg actually smell like.

GURLEY: Yeah, smells like the bottom side of a rock a little bit more.

TARANTINO: Yeah. I want to smell one that's like - is there one that's fruity?

BICHELL: Rae Ellen Bichell, NPR News. Transcript provided by NPR, Copyright NPR.