New Tests Needed For Drugged Driving. Federal Researcher Calls For Better Impairment Policies
Weed regulators in states where the drug is legal are on the hunt for ways to catch drugged drivers. Many of them have latched onto tests that determine the THC concentration in a driver’s blood or urine. But a researcher with the Department of Justice (DOJ) says testing THC levels in a person’s body is an inaccurate way of determining whether they are intoxicated.
During an episode of the DOJ podcast, Justice Today, Frances Scott, a researcher for the National Institute of Justice (NIJ) Office of Investigative and Forensic Sciences, said the popular model for determining weed impairment by testing THC concentration is flawed in a number of major ways. Scott said that scientists understand the effects and chemical interactions of alcohol consumption and determining intoxication based on the concentration of alcohol in the blood is “relatively easy.” But with marijuana, there are too many complicating factors involved to find reliably universal THC markers for intoxication.
Scott points out that there’s a big difference in intoxication levels when someone consumes edibles compared to smoking flower. Smoking produces a high that quickly escalates to a peak and then quickly recedes. Edibles produce a high that gradually builds and gradually recedes over many hours.
Edibles are also much more potent by volume because some of the Delta-9 THC that makes smokers high converts into the much stronger 11-hydroxy-THC in the liver. A driver who ate their weed instead of smoking it will be much more intoxicated than one who smoked the equivalent amount.
Scott says another issue is tolerance. Regular cannabis users — especially daily users — are able to consume large amounts of weed without experiencing the same level of effects as infrequent users.
In New Mexico, DWI law forbids driving while under the influence of marijuana “to a degree that renders [the driver] incapable of safely driving a vehicle.” Implied consent law makes it so that every driver must give their consent to be tested for drugs, but the law doesn’t specify a legal driving limit for THC or any other weed compound like it does with alcohol.
State police are left to their own devices to determine whether someone is high or not. Officers are trained to recognize signs that a person is under the influence of pot (like glassy eyes, impaired speech, inability to focus, dilated pupils and slow pupil reaction) through the Drug Recognition Expert certification program, but there’s no way to conduct any sort of roadside pothead test.
There have been a few attempts to invent an industrystandardized THC breathalyzer in recent years, but none of them have really panned out. There are even some products on the market that claim to accurately determine recent cannabis use.
One problem with these devices is that weed and alcohol do not interact with the body in the same way. It’s easy to test for the presence of ethanol vapors in breath (the way alcohol breathalyzers work). But marijuana smoke just doesn’t produce vapors like alcohol. Weed breathalyzers instead look for aerosol particles and those aren’t as easy to detect.
According to researchers at the National Institute of Standards and Technology (NIST) at CU Boulder, people exhale a million times more ethanol in a single breath than cannabis users exhale THC in 12 breaths.
The researchers were looking for a way to produce a standardized marijuana breathalyzer, but they said they were running into problems.
Not only is it tough to detect the physical evidence of cannabis in breath, initial research showed that all that evidence disappears within an hour of weed use.
As for blood and urine tests, the results are next to useless for determining if someone is currently high. The body stores THC in fatty tissues, where it can stay for days in infrequent users. For people who use cannabis regularly, THC can stay detectable for weeks or even months.
That means that someone can smoke weed in March and test positive for it in April. It would be ridiculous to claim that the drug’s effects last that long, and it would be really tough to convince anyone that the presence of THC in blood or urine was an indication that a driver was high while operating a vehicle.
Scott told the DOJ podcast that state regulators should stop trying to determine marijuana impairment by measuring THC in breath or body fluids. She noted that scientists aren’t even sure if THC is the right cannabinoid to be used as a metric when it comes to measuring impairing effects.
Scott also noted that current standardized field sobriety tests might not be the greatest metric to determine whether someone is impaired. These tests are designed to detect if someone is impaired by alcohol — not whether the skills needed to drive are impaired.
Standardized sobriety tests aren’t designed to detect the specific impairments that differentiate drugged driving from drunk driving. According to Scott, alcohol tends to negatively affect equilibrium and balance and alters the information that’s being received. Cannabis, on the other hand, tends to make users hyper-focused on specific aspects of their experience while losing focus on others.
New Mexico police are being trained to recognize signs of marijuana impairment that differ from signs of alcohol impairment. It’s a smart move, considering the vast differences between the two. But does it take into consideration the unique effects that weed has on perception?
Leading researchers say that currently there are no tests that appropriately measure those effects. But they are working on it. Scott highlighted the NIST work on the weed breathalyzer and a recentlycompleted DOJ-funded study that had participants smoke marijuana and take various field sobriety tests.
Scott said researchers were also taking a completely different tack by testing weed’s effect on peripheral vision.