Police in three California counties are testing what amounts to a breathalyzer for drug users – a device that some authorities and lawmakers said Wednesday is desperately needed now that voters have legalized recreational marijuana in the state.

When legalization takes full effect next year, California will become the world’s largest market for pot.

Yet California is among the states with legalized marijuana that are struggling to find a reliable test and gauge for marijuana impairment that can stand up in court and lead to convictions.

Law enforcement and academic experts say settling on such a test is complicated because drugs affect everyone differently and there is wide variation in the potency of pot and other drugs and the way they are consumed. As a result, there is no consensus on what level amounts to impairment.

The demonstration of the testing device Wednesday outside the California Capitol involved a Sacramento police officer using a cheek swab to collect saliva from another officer posing as a suspect.

The swab was then plugged into a walkie-talkie-sized device that shows within five minutes whether any of six drugs are present in saliva.

The equipment has been tested in Kern, Los Angeles and Sacramento counties under a law sponsored by Assemblyman Tom Lackey, a Palmdale Republican.

“We want this to become statewide,” Lackey said.

California Highway Patrol Sgt. Glen Glaser, who coordinates the patrol’s drug recognition expert program, said there are too many variables to rely on a saliva or breath test.

“The science is still developing,” he said. “The mere presence of a drug should not make a person feel like they’re subject to arrest if they’re not impaired.”

In addition, prosecutions are more difficult because there is no presumed level of drug intoxication in California, unlike the 0.08 percent blood alcohol level at which drivers are presumed drunk.

Michigan and Vermont recently authorized the tests that are also used in some other states and nations, according to Lackey’s office.

Lackey, a former California Highway Patrol member, unsuccessfully carried a bill two years ago that would have allowed police to use such “oral fluid” devices to test for drugs in much the same way officers currently use breathalyzers to test drivers’ blood-alcohol level.

Suspects are currently free to refuse to take the drug tests.

Police mainly rely on field sobriety tests if they suspect a driver is under the influence of alcohol or drugs. While drunken driving tests mainly test physical skills, drugged driving screening also looks for cognitive changes.

For instance, suspects are told to tip back their heads and estimate when 30 seconds have passed; some drugs make time seem to slow down while others produce the sensation that time has accelerated, Glaser said.

The state Assembly last month unanimously approved a bill requiring the CHP to create a task force to recommend best practices, policies and legislation involving tests for drugs. The bill now goes to the Senate.

Fred Delfino, product manager for Alere Toxicology, said the company’s device demonstrated Wednesday has an accuracy rate of 95 percent, enough to identify which drivers should be required to provide blood samples to show the actual level of intoxication.

More California police departments are using the saliva tests after a Kern County judge last year accepted the results as admissible evidence in a drugged driving case, said Lauren Michaels, marijuana and drunken driving policy expert for the California Police Chiefs Association.

The CHP and other agencies are cooperating with the Center for Medicinal Cannabis Research at the University of California, San Diego, as part of a two-year, $1.8 million study.

The center is analyzing and trying to improve the tests used by human drug-recognition experts and the saliva testing.

Researchers also are trying to learn if there is a particular level of marijuana intoxication that impairs driving, said Thomas Marcotte, the study’s chief investigator and co-director of the research center.

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