JUST BECAUSE THE PROPOSED MARIJUANA LAW ALLOWS ROADSIDE TESTS DOESN’T MEAN THEY WORK.
As was widely foreseen, the Liberals’ “Legalize marijuana in as awkward, truculent, and impractical a way as possible” legislation has created a whole new industry. I don’t mean selling weed, of course: we had that trade before. I’m referring to newspaper columns, op- eds, and interviews about how crummy this law is. I have about 120 deadlines in the next 12 months, and I could use this topic for ... 30? Maybe 40?
For now, let me cover just one aspect of legalization: the issue of roadside testing for marijuana impairment. The law contains provisions to permit this, and the constitutional angles are being smacked around like a tetherball. There seems to be a widespread assumption that because the law permits on-the-spot testing for impairment, such testing must be a practically possible thing; a solved problem.
Don’t count on it. There is no shortage of hustling inventors of roadside measurement devices for tetrahydrocannabinol ( THC), pot’s main mind- altering ingredient, in saliva. “Oral fluid” ( OF) testing is agreed to be the best chance for a practical breathalyzer- type device to test for drug impairment. Cops, whose love for unlawful strip-searches is well documented, would love to have you pee on command while they watch. But saliva represents very recent drug use better than urine anyway — in theory.
Alas, this theory is not strong. The pharmacokinetics of THC are incompletely understood when it comes to details like smoking versus vaping versus eating. In the scientific literature, there are hints that chronic users of the chronic may maintain constant high levels of THC in saliva even when not impaired. Marinol, the accepted therapeutic form of THC, poses problems. When all of this is mentioned in a paper, it quickly leads to discussion of maybe, possibly, hopefully using other metabolites of the cannabis plant as chemical indicators of impairment. Actual research lies in the future.
This makes the premise of THC detection devices doubtful. If measured THC levels don’t correlate reliably with impairment, criminal defence lawyers will pulverize the testing in courts. And there’s more bad news. The devices themselves are in their infancy, in the full sense of that word: undeveloped and clumsy.
I spent some time looking at research papers which examined devices from the most advanced line of oral fluid readers — the DrugWipe series from Germany. It makes for a rich vein of comedy. One sees researchers slowly realizing that spit samples, unlike breath samples, can have volumes varying over full orders of magnitude.
One watches their consternation at discovering that drug users sometimes suffer from dry mouth, precisely because they’ve taken a bunch of drugs. One sees positively hilarious figures for the statistical sensitivity and specificity of the devices: overall they seem not so bad at avoiding false positives (though the eventual constitutional standard on that side will be high), but in some independent tests they appear to let about two in every three people who just smoked cannabis off the hook.
The cutoffs for THC amounts representing “impairment” in other countries’ laws differ from place to place, and they are often predicated on old standards taken from urine tests in workplace settings. If you follow my trail o’ science, you will begin to pity the makers of the DrugWipe devices, who have to design their gadget to deliver a “yes”/“no” answer suitable to a whole world of differing guidelines. You will also begin to admire them, because some manifestations of the DrugWipe seem to do pretty well — with drugs other than cannabis.
It is not at all clear how large the problem of marijuana- impaired driving really is, or whether we can expect its magnitude to change just because of legalization. So far there are only the faintest signs of trouble from the U. S. states where recreational pot is legal.
Epidemiologists strongly suspect that pot does lead to auto accidents. The best summary of the evidence for this might be a meta-analysis done for the British Medical Journal in 2012 by a Dalhousie University team ( including top pot- and- driving scholar Mark Asbridge). Those researchers found that in the methodologically strongest observational studies, recent marijuana use, whether established by medical examination or self-report, seemed to be associated with roughly doubled risk of a serious auto accident. ( They were careful to reject cases and studies in which evidence of other drugs was present in accident victims, or left unclear.)
In their paper, they have to admit, having established the statistical connection, that it could result from confounding factors rather than marijuana effects. Maybe potheads are just the kind of people who are more reckless or less competent drivers, even when sober. That doesn’t seem improbable. And if it is so, the doubled risk is an overestimate.
In the context of other drugs we neither test for nor panic over — or even in the context of medical conditions like sleep apnea or glaucoma — a doubling of risk looks like nothing. The risk multiplier associated with being legally drunk is, as far as I can tell, well into double digits.
The multiplier for using a cellphone, according to one bravura analysis, is somewhere in the range of four to seven. That is why cellphone road deaths came to the attention of first responders and authorities relatively quickly, and why they are campaigned against so strenuously now. They are lowhanging epidemiological fruit. Cannabis probably isn’t. ( Don’t drive high, guys.)
THERE IS NO SHORTAGE OF HUSTLING INVENTORS.