Marijuana breath test under development by researchers PULLMAN, Wash., Nov. 29 (UPI) -- A breath test to detect marijuana may soon help police nab motorists who are driving while stoned. Researchers at Washington State University are working to develop a handheld device that will detect THC, the psychoactive component in pot, in someone's breath. According to WSU chemistry professor Herbert Hill, existing technologies -- such as those used by airport security screeners and federal agents to detect drugs and explosives -- can be re-purposed to test a person's breath for THC. Although 23 states and Washington, D.C., have laws legalizing marijuana for medical use, only four states, Washington, Colorado, Alaska and Oregon, have passed measures legalizing the drug for recreational use. The measure passed in Washington sets five nanograms of active THC per milliliter of blood as the legal limit for which a driver is considered impaired. Currently, police use blood tests to determine THC level, but those tests are not immediately available to officers on patrol. Hill suggests that at first the tool under development won't be able to pinpoint THC levels but will help law enforcement determine that a driver has been using marijuana. "We believe at least initially that it would lower the false positives that an officer would have," Hill said. State officials and law enforcement agencies say they welcome the efforts of Washington State University but indicate that a breath test for marijuana would be adopted only when it proves to be extremely reliable. According to the Washington State Toxicology Laboratory, 25 percent of the tested blood samples taken from suspected impaired drivers in the state tested positive for THC in 2013, the first full year marijuana was legal in Washington.