Cannabis is complex. And because of its federal standing, the plant will remain a mystery until it’s re/de-scheduled and scientists are allowed to study it. Until then, our understanding remains limited, which becomes a dilemma when states– such as California, Washington, Colorado, Oregon, Nevada, etc– start legalizing the herb because problems we don’t have solutions to are inevitably going to arise, like driving under the influence of cannabis. Cops do not yet have the equivalent of an alcohol breathalyzer or blood test for pot. So, it’s impossible to determine if someone is high when they get pulled over–aside from physical queues, of course, like bloodshot eyes and half-shut eyelids, or smelling like skunky flower. Despite the gaps in science and technology, people can still get a DUI for driving under the influence of THC. But this area of the law is so muddled that canna-DUI’s don’t always hold up in a court-of-law.
Andrew Pham, the scientific director of BelCosta Labs in Long Beach, testified on nearly 30 criminal cases in San Diego involving cannabis DUI’s between 2016 and 2017. Having worked with several of UC Irvine’s esteemed cannabinoid researchers, Pham’s understanding of the plant made him an asset to the San Diego Public Defender’s Office. In most of the cases, he explains, the defendant was taken to jail for suspected stoned-driving and required to take a blood test. “[The defendants] blood was drawn roughly two hours from the time arrest,” says Pham. “It was then sent to a lab to be analyzed for levels of THC, and its subsequent metabolites in the body.”
With alcohol, testing the blood is how law enforcement determines if a driver’s alcohol content is over .08. It’s not this way with cannabis, however, and that’s what makes it tricky. The two substances interact with the body in very different ways. “The largest difference from a chemical standpoint is that THC is what’s referred to as lipophilic, or fat soluble,” Pham says, “so those molecules much prefer to dissolve into your fatty tissues, such as your brain or your outer fatty body tissue, rather than stay in the blood. Alcohol is a water-soluble drug, so in general, it’s going to stay in your blood, and your blood will deliver the alcohol to your brain at a fairly constant rate over time.”
A study conducted by the National Institute of Health shows that after smoking a joint that has between three and 10 percent THC, the peak levels of THC in the blood will reach about 160 to 200 nanograms in about 20 minutes. 15 to 20 minutes later, however, the nanograms will drop to five or less. On a chart, if time is represented on the X-axis and THC-level is the Y-axis on the left, after smoking there would immediately be a huge spike and then a huge plunge to a base plateau level, Pham explains.
Additionally, the base plateau level is going to be different for every person depending on their body mass index (BMI), kinetics, and many other factors. “With a higher BMI you have more fatty tissues,” says Pham. “There’s going to be less [THC] in your blood. Also, less of it is going to reach your brain because of that. That’s why people who are heavier usually have a better tolerance. And that’s not just for THC–that’s for most drugs.”
Genetics also play a role in the difficulty of cannabis impairment testing. There are enzymes in our livers that convert THC into metabolites, which essentially inactivates the compound. These enzymes are controlled and produced by our genetics. Pham explains that if someone has a genetic difference or mutation in the gene, they won’t properly metabolize THC, which could artificially inflate the amount of THC that’s still in the blood. Additionally, a recent study also suggests that women feel the effects of THC impairment longer than men.
“With all of these factors at play, you can’t determine if someone is under the influence of THC with a single blood test taken two hours after an arrest,” says Pham. “The largest practical factor is tolerance. If you smoke every day, you’ll have a good amount of long-term metabolites in your system, which you can see in a blood test. I’ve argued that these metabolites are sort of a proxy for someone’s tolerance to THC because it means they’re repeatedly exposed to [the compound]. If you have a tolerance, the CB-1 receptors in the brain get down-regulated, so your brain expresses fewer of these cells. Thus, you’re not going to be quite as impaired as someone who has no tolerance.”
(For reference, THC binds to CB-1 receptors in the brain. These receptors are partly responsible for making us feel “high.”)
Thus, it’s currently impossible to determine via blood test (and any other current sobriety test) whether someone used cannabis 10 minutes ago or last night. In the cases Pham testified on, only four were found guilty. The rest, he explains, either ended in a hung jury or were found innocent. “The Public Defender’s Office really loves me now,” says Pham, as he laughs. “But I’m sure the DA hates me.”
NPR recently reported that scientists around the country are diligently working to create a chemical test and standard to determine if someone is impaired from cannabis-use; particularly because cops are depending solely on behavioral indicators to discern if someone is stoned.
Rae Ellen Bichell reports that Colorado has a THC blood test that law enforcement can use to show “presumed” impairment. If a person has more than 5 nanograms of THC per milliliter of blood, a court or jury can infer they are impaired, according to Colorado law. But as Pham expressed– and as Bichell reports– the way cannabis impacts the body is far more complex than a one-dimensional blood test. Scientists also don’t know whether 5 nanograms of THC per milliliter of blood means someones intoxicated or not.
The story cites a study in which researchers had 30 frequent cannabis users stay at a research facility for a month without any access to drugs and tested their blood daily for evidence of cannabis. In some cases, individuals tested positive for THC 30-days after research began. The study found that the participants’ bodies built up stores of THC that continued to seep into the blood, despite eliminating cannabis-use for a month. In those who regularly used large amounts of pot, researchers measured blood THC-levels above the 5-nanogram mark for several days after they’d stopped using the herb. So much for the accuracy of the presumed impairment test.
Furthermore, another study revealed that some occasional cannabis consumers might not show evidence of THC in the blood, even after immediately lighting up. According to the study, a few occasional consumers puffed in front of the researchers, and THC was not detected in the blood when tested. Why? That has yet to be determined. But those occasional cannabis consumers likely wouldn’t have been detected during THC’s six-hour impairment window. The study notes they’d likely be overlooked in a test.
A wealth of research, discovery, and innovation lies ahead. But the root of the problem is the fact cannabis is a schedule-one substance, therefore prohibiting the scientific investigation the cannabis world desperately needs.
“You can’t [determine cannabis impairment] with any field sobriety test because the majority of them are actually looking for either alcohol, barbiturates or opium impairment,” says Pham. “None of them are validated for cannabis, so you can’t do it that way. You can’t determine if someone’s under the influence from a blood test. There’s no THC breathalyzer, yet. So, right now, there really isn’t any way to establish cannabis impairment in a court of law.”
