re: #872 wrenchwench

So for legal purposes, they are assuming that what works for alcohol is close enough for marijuana? I was wondering how this would play out with legalization becoming widespread. Will drivers have to submit to blood tests instead of being able to opt for the breath or urine tests?

Consider the questions rhetorical if you like.

If you want I’ll go digging for the studies, but here’s the nutshell. There was a landmark study a couple of decades ago that showed that there was no measurable physical impairment at less than 5 ng/mL (nanograms/milliliter) of THC/blood. At 5ng/mL (aka 5ng) the impairment was measurable in a statistically significant sample — memory (take your grains of salt) says it is comparable to a 0.05 BAC. That in turn, of course, means that a lot of people will eventually wind up arguing that either the THC thresholds for legal impairment need increased or the BAC decreased, but that’s a digression.

What makes this more complex is that the primary psychoactive compound is pretty much undetectable by anything other than an actual blood test. Urinalysis, breath, and saliva tests all test secondaries. Ironically, the problems with saliva make it the best alternative for blood in this case. But it’s still getting into the whole invasive procedure question that exists already for involuntary blood tests. Not least, because the saliva test can coincidentally be used for a DNA test.

Personal opinion: I think the saliva test will wind up being allowed by the courts, and that we’ll wind up with something along the lines of .8 ng being the magic line (approx one really strong or two moderate cigarettes within the preceding two hours, assuming a 150 pound person.)