Is a marijuana breathalyzer close to being ready for use?

Measuring the THC in a driver's body is only part of determining whether they are actually impaired

Laws in California and a fair number of other states have lowered the restrictions on some marijuana use, decriminalized possession of small amounts or permitted the use of medical marijuana. Four states and the District of Columbia have legalized marijuana and efforts continue in California to add the state to that list.

This has led to a concern that the legalization of marijuana and the likely increase in recreational use could lead to an epidemic of motor vehicle crashes due to marijuana-impaired drivers.

For law enforcement, it is a significant problem. Unlike alcohol, the chemical in marijuana that causes impairment, THC, behaves in a very different manner and many of the testing paradigms are inapplicable to determining impairment.

Fat-soluble

The first problem is that THC dissolves in fat, unlike alcohol, which readily dissolves in water. Alcohol will evenly disperse throughout the body via the blood, and this allows blood and breath tests to reasonably approximate levels of intoxication that correspond to a single number.

Over the decades, researchers have concluded that 0.08 percent blood alcohol content equates to sufficient impairment to a person's cognitive abilities to make it unsafe for them to operate a motor vehicle.

THC breathalyzer

A California company has announced that it has developed a device that can produce an accurate measurement of THC using a person's breath. This may seem like the holy grail of drug testing, allowing an officer on the side of the road to obtain a real-time measurement of THC and, so the argument would go, the level of the driver's impairment.

Casual or heavy user?

There is one problem. THC behaves very differently in the human body from alcohol, which makes coming up with a standard for impairment difficult.

Because THC is fat soluble, it is readily absorbed in the fatty tissue of the body. This means when a casual user smokes a joint, within a few hours, they may have virtually no THC in their blood, but could be impaired, yet still would able to pass most drug test standards.

On the other hand, a heavy user will have THC saturated throughout their body and long after they have smoked their last joint, their body is leaching THC into their bloodstream. They could have gone days without smoking any marijuana, yet could still fail a drug test for THC.

What is 0.08 for THC?

The head of the California company that claims it has a viable breath testing device for THC noted that the drug levels necessary for impairment under state laws currently in place are "completely arbitrary." He goes on to state that he "would argue that they are useless."

He also points out that the real question will be how to determine what level of THC in the body actually indicates impairment.

In a criminal case, the standard for a conviction is guilt beyond a reasonable doubt. Given the vagaries of how THC behaves in different human bodies, it is unlikely that a simple reading, like 0.08 BAC for alcohol, will ever scientifically meet that standard. Of course, legislatures have been known to create arbitrary standards that have little scientific basis, and it may take years for researchers, legislatures and law enforcement to agree.