A marijuana breathalyser could soon become a common device used by US authorities to determine whether a driver is impaired by the drug.

In the past few years an increasing number of states have legalised the use of marijuana, despite some law enforcement organisations pushing back against the changes.

Police have previously argued that legalising weed could result in a growing amount of motorists driving under the influence of the drug.

Current methods of testing, including oral fluid, blood and urine, can detect the presence of THC, the main psychoactive compound in marijuana, weeks after the subject ingested the substance.

Head of the New Jersey State Association of Chiefs of Police, Christopher Leusner, said this makes it incredibly difficult to determine whether someone is impaired at the time of driving.

media_camera The marijuana breathalyser can detect tiny amounts of THC on the breath. Picture: Hound Lab

“With alcohol, if you have over 0.08% in your blood, there’s the presumption that you’re intoxicated,” he told The Philadelphia Inquirer.

“There hasn’t been a blood test or a breath test that can determine if you’re impaired by marijuana.”

But a device created by US company Hound Labs claims to have solved this problem.

The Hound Breathalyser is able to accurately identify recent marijuana use by measuring THC in the breath.

THC is only detectible on the breath for a few hours, correlating with peak impairment.

“Breath is best for determining recent marijuana use and providing the right objective data to make informed decisions about possible impairment,” the Hound Labs website reads.

“The Hound Breathalyser allows law enforcement and employers to fairly address the safety concerns associated with marijuana impairment without unjustly accusing individuals who legally and responsibly use cannabis.”

media_camera The device allows users to determine recent marijuana use, unlike other testing methods. Picture: Hound Lab

A senior fellow at the Brookings Institution, John Hudak, told the publication that the device was a “game changer”.

“I’ve been saying for years it’s only a matter of time before someone developed the technology and got the science right,” Mr Hudak said.

“That time apparently is now. And they’re going to make a hell of a lot of money selling it to law enforcement agencies across the US and Canada.”

Results from a second clinical trial earlier this year confirmed THC is present in breath for two to three hours after smoking, which is the same duration as peak impairment according to government studies.

As THC is at such low levels in the breath, the device has been created to be a lot more sensitive than regular alcohol breathalysers.

“The ability to capture breath and measure such low concentrations of molecules represents a significant breakthrough and we hope to continue to collaborate with Hound Labs on clinical studies to advance the field of breath diagnostics,” Dr. Kara Lynch from the University of California, San Francisco said in February.

Originally published as New breathalyser can detect marijuana