Another expert outlined the problems with such tests.
"Because THC, the active ingredient in marijuana, can be detected several weeks after use of marijuana, it is hard to determine with certainty if a driver testing positive for marijuana is indeed impaired by the substance at the time of testing," said Dr. Guohua Li, a professor of epidemiology at Columbia University in New York City.
So more research is needed. "This issue is especially urgent and important in light of the ongoing epidemic of drugged driving and increased permissibility and availability of marijuana worldwide," Li said.
While recognition that driving under the influence of marijuana is a problem is a first step in finding ways to curb it, Jan Withers, national president of Mothers Against Drunk Driving (MADD), stated that "drunk driving remains the primary threat to our families on the road."
However, she added, "this study underscores the importance of the work that MADD is doing to support people who have been victimized by drugged driving and recognize law-enforcement's efforts to pioneer effective strategies to stop drugged driving. Notably, it shows the increased danger posed by those drivers using both alcohol and drugs."
For more about drugged driving, visit the U.S. National Institute on Drug Abuse.
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