As more U.S. states legalize marijuana for both medicinal and recreational purposes, traffic cops face an interesting new dilemma. Pot may be legal, but driving under the influence is not; and the available methods used to test for the presence of marijuana in a driver’s system are far from adequate.

We can test for cannabinoids in a person’s saliva, urine, or blood; but these residues can linger in the body for days or weeks after a person has smoked. Most police departments use blood testing and have gotten convictions based on these results. But these blood tests cannot be done on the side of the road, they must be processed in a lab, delaying the test results. And when the results do eventually come in, they’re a bit sketchy. According to some studies, frequent users can still test positive several days after they last used.

At present, there is no reliable way to tell if a person is under the influence at the time of the arrest. But researchers are working on a solution to that problem.

A former Canadian Mounty named Kal Malhi, together with co-inventor Dr. Raj Attariwala, has a patent pending that is generating a lot of media buzz. They have developed a device called the Cannabix Marijuana Breathalyzer. It is designed to detect the presence of THC in the lungs, and will work much the same way as current alcohol breathalyzers. They still have a lot of product testing to undergo before the device is ready for duty, but they have already begun to market it to police departments in the U.S., as well as to big companies who might wish to use it to test employees after an accident.

Washington State University is also developing a breath test based on something called “ion mobility spectrometry,” a technology currently used by airport security to detect explosives and chemical weapons. They plan to begin testing their design in 2015.

Breath testing might be an improvement over our current methods of testing for marijuana intoxication, but there are still some underlying issues that remain unresolved. Most importantly, detecting the presence of THC in a person’s system does not necessarily prove they are intoxicated. Different people metabolize cannabis in different ways, and are affected by it differently. Habitual users tend to retain cannabinoids in their system for longer periods of time, yet they are not as impaired as more casual users who consume the same dose. Plus, different strains of marijuana may be metabolized at different rates, especially strains designed for medical use, which tend to metabolize more slowly.

With alcohol, we have a clearly defined blood-alcohol level of .08 percent, beyond which nearly everyone starts to display certain signs of impairment. But with pot, there is no universal standard of measure that says, “over this limit you are stoned.” Some states have passed measures which set the legal limit at 5 nanograms per milliliter of blood, but there is no research that shows that level indicates impairment. Habitual smokers or medical marijuana patients might test above that level all the time, even when they are not under the influence. But don’t expect that to stop zealous cops and prosecutors from throwing them in jail.

More research is needed to better determine how the body processes cannabis, how to measure levels of active cannabinoids in the body, and how those levels correlate with intoxication and impairment. Until we have that data, we should be wary of legislation which sets strict limits and potentially puts innocent people at risk of prosecution. Because with breath-testing technology on the way, that risk is greater than ever.

One thing is for sure: driving while impaired is a bad idea. Whether or not it’s legal, cannabis users must smoke responsibly, and not put themselves and others at risk by driving while stoned. Period.