As cannabis bans are relaxed in more U.S. states, the race is on to develop an instant roadside breathalyzer for police to test drivers who may be taking the "high" road.

Vancouver-based Cannabix Technologies, founded by a retired RCMP officer, expects to be first out of the gate with a "pot breathalyzer" — a handheld device similar to those used to detect alcohol.

Cannabix won't give an estimate of when its product might go on sale, but has a prototype undergoing in-house testing.

Other hopefuls, such as Colorado-based Lifeloc Technologies and a chemistry professor-PhD student duo at Washington State University, are still busy in the lab.

The devices under development all aim to accurately detect the presence of THC, the psychoactive component in cannabis. But so far, they can't provide enough evidence of impairment by themselves.

"I think the first breathalyzer on the market will be a simple 'yes' or 'no' for the presence of THC at the time of the test, and in that sense it won't provide a quantitative evidential measure," said Barry Knott, the chief executive of Lifeloc, which already makes alcohol breathalyzers.

Potential size of the market unclear

The size of the potential market is unclear, owing to widely varying estimates of cannabis use, and unreliable data on those driving under its influence.

But developers say they will be able to sell pot devices for a lot more than the ubiquitous alcohol breathalyzers.

Lifeloc sells alcohol breathalyzers for $300 to $400 but expects to charge $2,500 to $3,500 for its cannabis version.

A roadside breathalyzer would replace a complicated assortment of costly blood and urine tests that can take days to get a result. But even these tests are a long way from showing impairment, as the science on how cannabis affects driving is far from settled.

How much is too much?

The National Highway Traffic Safety Administration, in a paper this year, said cannabis impairs psychomotor skills, attention, lane tracking and cognitive function, but not enough is known about how much is needed to affect driving performance.

Whether marijuana is smoked or ingested also dramatically changes how the body processes it. It's also difficult to isolate the affects of cannabis in crashes if drivers have also consumed alcohol and/or other drugs.

Cannabix founder Kal Malhi initially aims to cater to Canada and the U.S. states that have zero tolerance for THC, hoping his device - designed to confirm police observations - will be able to accurately detect THC up to two hours after consumption.

"If this is just a matter of showing how many people have THC in their systems, then it's essentially useless," said Steve Sarich, who runs a cannabis advocacy group and serves as an expert witness for cases involving THC-related impairment.