Pubdate: Sat, 22 Apr 2017
Source: National Post (Canada)
Copyright: 2017 Canwest Publishing Inc.
Author: Colby Cosh
Page: A16


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

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 low-hanging epidemiological fruit. Cannabis
probably isn't. (Don't drive high, guys.)
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MAP posted-by: Matt