“Regulate Marijuana Like Alcohol” was the tagline for the successful legalization campaign in Colorado. While the comparison to alcohol regulation made it possible for Colorado voters to accept the idea of legalizing marijuana, it also prompted them to ask: “Where’s the marijuana breathalyzer?” Now we’re witnessing a scramble by drug-detection technology companies to answer that question.

A new study in the Journal of Clinical Chemistry, “Cannabinoids in Exhaled Breath Following Controlled Administration of Smoked Cannabis,” found that a person who has smoked pot will exhale measurable amounts of active THC within 30 minutes to two hours. All 13 of the chronic pot smokers in the test produced a positive result 53 minutes after smoking a joint with 6.8 percent THC; over half were positive after two hours, but only one tested positive after four hours. Among the 11 infrequent tokers tested, 10 were positive within the hour, and seven of them still tested positive after 90 minutes.

These are preliminary experiments, and there are still problems with the technology. The breath tests for THC, unlike the alcohol breathalyzer, don’t measure how much THC is in a person’s system -- only that there is some active THC present. Thus, these tests wouldn’t answer any questions about whether a particular driver is over the five-nanogram “per se” limit that exists in Washington and Colorado. However, it would be proof of violating a zero-tolerance limit, as exists in over a dozen other states -- and, in any state, a future THC breathalyzer would probably be reason enough for a police officer to arrest you on suspicion of DUI and take you in for a blood test.

But soon there may be no need to do even that. Another technology, called the V-Chip, is being developed by Lidong Qin and Ping Wang of the Houston Methodist Research Institute. They received a $2.1 million grant from the National Institute on Drug Abuse to develop a pocket-sized drug test for use in hospital emergency rooms that is easy, fast and accurate.

V-Chip is about the size of a credit card and contains antibodies for 50 different drugs and drug metabolites. Add a drop of blood, serum, urine or other bodily fluid to the chip, and any drug or drug metabolite it contains will bind to the antibodies and cause a reaction that creates a bar graph of the substances detected. Tests show the V-Chip is accurate to the nanogram-per-milliliter level, which is exactly the standard used to determine THC levels in Washington and Colorado, as well as in Nevada, Ohio and Pennsylvania.

Once the V-Chip is perfected, it isn’t difficult to imagine its embrace by law enforcement. If a reliable technology exists to prove that a driver is over
the five-nanogram limit during a police encounter, there will be inevitable political pressure to allow its use. Currently, drawing blood from a suspect can’t be done without an arrest and a warrant, as courts have ruled it an invasive procedure requiring a higher standard of suspicion. But when the amount of blood needed is no longer enough to fill a test tube -- drawn by a nurse with a long needle -- and instead becomes something as simple as the self-administered pinprick diabetics use to test their blood sugar, then it’s only a matter of time before courts find that the importance of traffic safety outweighs the slight inconvenience to the driver under suspicion.

So the roadside detection technologies are coming, but the biggest problem isn’t whether they’re accurate; it’s whether they’re telling us anything useful. The reason the alcohol breathalyzer is a successful technology is because it tells us how much alcohol is actively impairing a driver, and it gives a reliable indicator of that in a dose-dependent fashion. Yes, there are the extremes -- the petite woman who’s too drunk to drive at .04 BAC, or the obese alcoholic who can pass a driving test at .15 BAC -- but by and large, people blowing .08 BAC are too drunk to drive, and people who consume x drinks per hour at y body weight are going to end up drunk.

Marijuana doesn’t work that way. Even the National Highway Traffic Safety Administration admits: “It is difficult to establish a relationship between a per- son’s THC blood or plasma concentration and performance-impairing effects. Concentrations of parent drug and metabolite are very dependent on pattern of use as well as dose. It is inadvisable to try and predict effects based on blood THC concentrations alone.” The future marijuana breathalyzer or V-Chip can tell us if someone has used marijuana recently, but not whether that use has rendered them unfit to drive.

However, is that distinction enough for the general public? It will be hard to convince many people that someone can smoke a joint and safely get behind the wheel within an hour, even if it may be true. By legalizing marijuana with comparisons to alcohol, we may have unfortunately locked ourselves into a frame that demands an alcohol solution.