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.
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).
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.
The participants’ bodies had built up stores of THC that were continuing to slowly leach 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.
With the legalization of pot in many states, it is clear where the future is heading. That means there will be more cases of driving under the influence of marijuana. This means DUI lawyers will now have to familiarize themselves with how marijuana metabolizes in the body in addition to alcohol.
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