Stanford Researching Roadside Marijuana Saliva Test Is Wasting Its Time

Cop Pat Down
“Well, son, if you just stopped smoking pot for a month so all that THC would be out of your system, we wouldn’t be having this interaction, now, would we?”

Once again, another team of scientists is trying to perfect the technology for police to detect marijuana use in drivers during roadside stops. This time, it’s researchers at Stanford University who are trying to create a handheld saliva testing device for THC.

(USA Today) Officers who suspect marijuana intoxication could use a cotton swab to wipe the inside of a driver’s mouth, test it in the new device (called a potalyzer) and get results viewable on a smartphone or laptop in just a three minutes, according to a Stanford news release.  Currently, officials rely on blood, breath or urine tests that aren’t always accurate. Saliva tests exist, but also aren’t completely accurate.

Stanford’s device can show THC in the range of 0 to 50 nanograms per milliliter of saliva, within most measurements of impairment, the release states. Colorado law says drivers with five nanograms of active THC in their blood can be prosecuted.

There is so much wrong with this, but we marijuana law reformers are somewhat to blame. For about a decade now, we have been imploring society to “treat marijuana like alcohol.” By doing so, we activated the alcohol frame for marijuana. That was a smart move to get people to understand the relative safety of marijuana and that it could be a taxed and regulated substance like alcohol. But it came at the cost of getting society to believe that marijuana is like alcohol, so now they want to know where is the Breathalyzer for pot?

FARS Driving Fatality Rates 1994-2013
Well, that’s odd. Seems that there are fewer people crashing and dying since we legalized marijuana… especially where we legalized marijuana.

Of course, in this respect, marijuana couldn’t be more unlike alcohol. The science behind Breathalyzers is pretty solid. Human bodies metabolize alcohol molecules at a set rate based on how much was consumed and how large the body is. Detection of alcohol molecules in the breath correlate quite well with levels of impairment. With very few exceptions, somebody at 0.08 blood-alcohol content (BAC) is too impaired to drive, whether they are a petite ballerina or a burly lumberjack.

The science behind detecting marijuana impairment, however, is not reliable. Human bodies metabolize THC molecules at wildly unpredictable rates based on each individual’s body fat, energy levels, and history of consumption. Detection of THC molecules in the bodily fluids doesn’t correlate at all with levels of impairment. The burly lumberjack who’s smoking his first joint may be far more impaired at just 5 nanograms of active THC than the petite ballerina who’s a daily wake-n-baker who just cleared a bong.

Even the National Highway Traffic Safety Administration admits this:

(NHTSA) It is inadvisable to try and predict effects based on blood THC concentrations alone, and currently impossible to predict specific effects based on THC-COOH concentrations. It is possible for a person to be affected by marijuana use with concentrations of THC in their blood below the limit of detection of the method.

Pharmacological effects of marijuana vary with dose, route of administration, experience of user, vulnerability to psychoactive effects, and setting of use.

Tolerance may develop to some pharmacological effects of [THC]. Tolerance to many of the effects of marijuana may develop rapidly after only a few doses, but also disappears rapidly.

Another problem with the idea of saliva testing is that if you’re really pulling someone over who’s had too much to toke, they are going to have dry mouth like the Sahara. Cops may not be able to get a decent saliva sample in such a case.

If a roadside test accurately determined that a person was too stoned to drive, I’d be all for it. But all these tests can ever accomplish is just determining if someone consumed marijuana in the past. Arbitrary per se DUID laws, like Washington State’s 5 nanogram limit, serve only to detect drivers who smoke pot, not drivers who are too impaired. Regular cannabis consumers like me never achieve a THC level below the residual 5 nanograms we could have after a full night’s sleep.

We must push back against this. It’s not as if legalization invents cars and marijuana smokers who drive them; we’ve been here for decades. Year after year, we see highway traffic fatalities and crashes declining, even as year after year we keep legalizing medical and recreational marijuana. The potalyzer is a solution in search of a problem.

Russ Belville
About Russ Belville 199 Articles
Russ Belville - or "Radical" Russ, as he is known on-air - hosts The Marijuana Agenda, a live news and talk radio program for the cannabis community, weekdays at 3pm Pacific on  The show is based in Portland, Oregon, but "Radical" Russ has traveled over 300,000 air miles in the past five years, bringing his show to report live from hundreds of cannabis conferences, marijuana expos, hemp festivals, and legalization events in over 70 North American cities.