Marijuana can be detected in a person’s blood at a level that might affect driving for weeks after “the last intake” according to a new study appearing in the journal Clinical Chemistry, as Bengt Halvorson reports in The Car Connection.
Sean Kane writes in iTechPost: “This is important for laws pertaining to marijuana use and how it relates to operating motor vehicles, since enforcement of any marijuana laws requires testing for intoxication, as well as a cutoff for that intoxication.”
The abstract says that in order to do the study, researchers collected blood from 30 chronic daily male cannabis smokers who lived in a secure research unit for up to 33 days.
Halvorson quotes the study:
‘Our results demonstrate, for the first time as far as we are aware, that cannabinoids can be detected in blood of chronic daily cannabis smokers during a month of sustained abstinence,’ said the paper’s conclusion statement. ‘This is consistent with the time course of persisting neurocognitive impairment reported in recent studies.’
At the same time that the legalization of marijuana — whether for recreational use in Colorado and Washington State, or for medical use (in 18 states and the District of Columbia according to ProCon.org) — has been moving fast, there has been little research about how daily marijuana smoking affects driving safety, Halvorson writes. He says it is surprising that a study like this one appearing in Clinical Chemistry had not been done before.
Kane quotes Dr. Karylin Huestis of the National Institutes of Health and an author of the study: “These data have never been obtained previously due to the cost and difficulty of studying chronic daily cannabis smoking over an extended period.”
Part of the problem, Halvorson writes, is that with people who smoke marijuana on a regular basis, THC, the active ingredient, is present in the blood in variable amounts that do not necessarily decrease predictably like blood-alcohol.
He quotes from the study: “Acute impairment is well documented for hours after cannabis intake, whereas the persistence of chronic impairment is less clear,” the authors state. Cannabis is second only to alcohol for impaired driving and motor vehicle accidents, Halvorson notes. He then adds:
To help keep it all in perspective, drunk drivers are ten times more likely to be the cause of fatal car accidents than stoned drivers. Yet results from a 2005 study in the journal Addiction found that regular cannabis smokers had about ten times the level of car-crash injuries when compared with those who abstained or used infrequently.
Halvorson writes that what is needed is a unified “per se” drugged driving policy, in other words, one in which any detectable amount of a controlled substance could be potential grounds for finding a driver guilty of impaired driving.
Image by Jeffrey Beall.