Study: Marijuana Breath Test Could Offer Alternative To Controversial Blood Draws For Pot DUIs


By Steve Elliott
Hemp News

Colorado and Washington, with their new recreational marijuana laws, and the 20 medical marijuana states are grappling with the question of driving under the influence of cannabis. Lawmakers seem to feel some action is required, although there hasn't been anything remotely resembling a rash of marijuana-related accidents, as has been the case with alcohol.

A recent study published in the peer-reviewed medical journal Clinical Chemistry suggests that a marijuana breath test might work for law enforcement to test for THC in drivers, like the "breathalyzer" test performed to determine the level of alcohol intoxication, reports Matt Ferner at The Huffington Post.

The THC blood test which is currently used remains controversial, especially since it involves blood being drawn from the suspect.

According to the new study, scientists collected breath samples from folks who used marijuana four or more times per week, and also from occasional users (fewer than two times per week) after they smoked a joint containing 6.8 percent THC.

THC turned out to be the main cannabinoid found in breath samples; it is generally the one, as marijuana's main psychoactive compound, which is believed to affect driving ability. No breath samples contained THC-COOH, the cannabis metabolite that is formed in the body after marijuana is consumed. Only one sample contained CBN (cannabinol), an oxidative product of THC being broken down. CBN is slightly psychoactive, but much weaker than THC.

All breath samples for the heavy smokers in the test group tested positive for THC just under an hour after smoking marijuana. Fewer samples tested positive as time passed, and about four hours after toking up, only one heavy user's sample still tested positive.

About 90 percent of the breath samples tested positive for THC among the occasional smokers just under an after after toking, and continued to test positive for about another hour and a half. One occasional smoker had no detectable THC in the breath sample.

"Breath may offer an alternative matrix for testing for recent driving under the influence of cannabis, but is limited to a short detection window," the researchers conclude.. The detection window is believed to be between 30 minutes to two hours after smoking cannabis.

Psychoactive effects of cannabis wear off within three to four hours, with THC blood levels peaking at about five to 10 minutes after toking and then gradually falling, according to a study from the Marijuana Policy Project.

THC blood tests, involving blood draws, are currently the norm in most states that regulate marijuana use while driving. Many of them have set the level at five nanograms of THC per milliliter of blood, above which drivers are considered "under the influence" of marijuana, despite the fact that there's no solid research establish a correlation between 5 ng/ml and driving impairment.

You see, unlike blood alcohol levels, which actually have a direct correlation with impairment, THC blood levels don't necessarily indicate any impairment at all, in the real world -- only in the faulty laws written up by panicked legislators.

In one study, six of 25 participants who had consumed cannabis still tested positive for active levels of THC after seven full days of abstaining.

As pointed out last year by Colorado Sen. Pat Steadman (D-Denver), THC is fat-soluble, which means blood levels could remain above the legal limit for days after the individual last legally used marijuana. The user wouldn't appear high, and wouldn't be impaired, but would still be charged for marijuana DUI. With this in mind, Steadman tried (and failed) to exempt medical marijuana patients from the cannabis DUI bill.

A pot reporter for Denver Westword illustrated Sen. Steadman's point in 2011, when he tested nearly three times higher than Colorado's proposed legal limit after a night of sleep and not smoking marijuana for 15 hours.

(Photo: MotherJones)