In his past life as a general-duty constable with the Royal Canadian Mounted Police, Kal Malhi regularly stopped drivers exhibiting slurred speech, impaired judgment and other signs of intoxication. Many of them were drunk, but he often suspected that some of these motorists were not tipsy but rather a few tokes over the line.

Malhi believed they were driving under the influence of marijuana, but he often had no way to prove his hunch beyond a reasonable doubt, a quandary that faces law enforcement agencies around the world and which a small crew of entrepreneurs and researchers are working to resolve. “What’s happened is people are choosing not to drink and drive, but they’re not hesitant to smoke up and drive, and I believe that with the legalization of marijuana coming on board and marijuana becoming more accepted in society, we need a tool for law enforcement to stand behind,” Malhi said in a telephone interview Wednesday.

While numerous studies demonstrate that driving while under the influence of cannabis is not as deadly as driving drunk, the drug still impairs drivers and presents a safety risk that's contributing to a quickly rising rate of fatal car accidents and injuries. Police, academics and companies are working to reduce that risk, but it can be a difficult task when the existing methods for testing if people have smoked marijuana recently are fallible or fairly easy to undermine in court. States such as Washington and Colorado, which have embraced legal pot in recent years, have created a new sense of urgency for law enforcement officials trying to stop stoned drivers.

Police officials currently rely on blood, saliva and urine tests, which detect use of the drug days prior to testing, not just whether a person is currently impaired. They are often seen as too invasive, as the evidence they collect can be used to serve other purposes such as DNA profiling, according to Sarah Schielke, a defense attorney who specializes in driving under the influence of marijuana cases at the Life & Liberty Law Office in Loveland, Colorado. As such, they can all be easily defended against in court, leaving a police officer without enough evidence to secure a conviction.

“The science is very murky on what good indicators are for impairment by marijuana because someone could just smell like it or have consumed it a few hours ago and it’s difficult to say if they’re impaired or not,” Schielke said.

That’s why Malhi co-founded Cannabix Technologies, a Vancouver company that has spent the past eight months creating, honing and patenting a breathalyzer that tests for THC, the ingredient in marijuana that gets users “high.” Malhi said his hope is that the development of such a breathalyzer will eliminate the guesswork in enforcing the laws governing driving while under the influence of marijuana. The device will not only tell law enforcement officers whether someone smoked weed in the past three hours, making it easier for them to obtain convictions, but also exonerate people who are not actually impaired but still contain a baseline of THC in their bloodstream.

Malhi said he expects his firm to have a workable marijuana breathalyzer prototype manufactured by the end of February, and to have governments considering it for medical approval by summer. Washington State University, meanwhile, is researching how to test for THC via breath.

“Currently, when charges are brought against a person, courts are reluctant to approve the charges based on just the opinion of a police officer, and there are lots of defenses people can come up with,” Malhi said. “Without a scientific tool to confirm a police opinion that someone has THC in their system, the courts don’t really [tend to] approve the charges, and the conviction rates are not very high."

But the day when every police cruiser is stocked with alcohol and marijuana breathalyzers is still a ways off. They have to first be approved by governments, police forces will need to dedicate funds to purchasing the devices, and production will need to keep pace with demand. In the meantime, Schielke said, it's important that police officers, attorneys and the general public understand that the verdict on driving while under the influence of marijuana is not yet in.

“The law has not gotten it right on its first try; it has a long way to go,” she said. “The only way we’re going to get there is with more science."