Saliva testing is being pushed by a group of Michigan legislators and by the Michigan State Police. But researchers who have studied the method said results are inconsistent and misleading, especially when applied to the 100,000 plus residents who are allowed to use medical marijuana.

The saliva test would add evidence needed to justify an arrest, just as portable breath testers do in drunk driving cases. But the two kinds of testing aren’t comparable, said Brett Ginsburg, an associate professor at the University of Texas Health Science Center at San Antonio: Saliva testing attempts to determine a subject’s level of THC, the psychoactive component of marijuana, but because THC affects the brain through the nervous system, and because saliva is outside the nervous system, a saliva test is a poor indicator of whether behavior might be impaired.

At a hearing last week, medical-marijuana advocates slammed saliva testing as a violation of their right to use the drug freely under the State’s medical marijuana act. State Representative Dan Lauwers said afterward that he would support an amendment to the proposal that would waive the test for licensed medical marijuana patients.

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