NPR on trying to create DUI regulation for marijuana
September 6, 2016
NPR had a good segment on this today: The Difficulty Of Enforcing Laws Against Driving While High. Definitely well worth a listen.
I had a few reactions in a comment that ended up being post-length, so here you go.
The major discussion of the segment was two-fold and I think illustrates where policy based on the science can be helpful, even if only to point to what we need to know but do not at present.
The first point was that THC hangs around in the body for a very long time post-consumption, particularly in comparison with alcohol. Someone who is a long term chronic user can have blood THC levels that are…appreciable (no matter the particular threshold for presumed impairment, this is relevant). Some of the best data on this are from the laboratory of Marilyn Huestis when she was, gasp, an intramural investigator at NIDA! There are some attempts in the Huestis work to compare THC and metabolite ratios to determine recency of consumption-that’s a good direction. IMO.
The second argument was about behavioral tolerance. One of the scientist interviewed was quoted along the lines of saying the relationship between blood levels, repetitive use and actual impairment was more linear for alcohol than for THC. Pretty much. There is some evidence for substantial behavioral tolerance, meaning even when acutely intoxicated, the chronic user may have relatively preserved performance versus the noob. There’s a laboratory study here that makes the point fairly succinctly, even if the behavior itself isn’t that complex. As a counterpoint, this recent human study fails to confirm behavioral tolerance in an acute dosing study (see Fig 4A for baseline THC by frequency of use, btw). As that NPR piece noted, it would be very valuable to get some rapid field screen for THC/driving – relevant impairment on a tablet.
DrugMonkey 
September 6, 2016 at 9:39 pm
So in other words, given that the pigs may not be operating with the best scientific knowledge to hand (as ever!), govern your bong-hitting self accordingly!
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September 7, 2016 at 12:27 am
I was on a jury for a DUI case once.
The guy had a beer or two at a bar then drove home. He was poor, driving a beater of a car. The police officer claimed he was swerving and pulled him over. Driver testified that the police car drove at high rate of speed until right behind him, then tailgated. He was freaking out. He said he might have crossed the fog line once or twice because he was looking in the rear view mirror wondering what was up with the cop.
Anyway, the driver blew a 0.06 and 0.08 was the legal limit. That was the only physical evidence we saw. The judge told us the law was that he is guilty if either he blows above the legal limit OR if he was driving impaired. The policeman gave him a field sobriety test (balance on one foot, etc) and said he failed. A second policeman testified and said it was borderline.
We voted to acquit.
After the trial, the guy’s attorney told us he had already spent 30 days in jail because he missed an earlier hearing. His car broke down and it was like a two hour bus trip with multiple transfers through suburbia to get into the city. It sucks to be poor.
Anyway the point of this story is that the law already exists. If they can pass a field sobriety test they are fine. I think now the usually do those on video, so the jury can look at the video and judge for themselves.
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September 7, 2016 at 9:22 am
“If they can pass a field sobriety test they are fine.”
On the surface this makes sense, but a field sobriety test, such as walking a straight line or touching your nose, specifically measures motor impairment. Those forms of motor impairment are the result of alcohol’s strong effects on the cerebellum.
The first problem is that marijuana doesn’t have the same motor effects.
The second problem is that even with alcohol, motor impairment is not necessarily what causes accidents. Impaired judgment is a more significant factor. The questions are whether marijuana impairs the kinds of judgments that are important for operating a motor vehicle; what level of THC causes those impairments; and how those impairments can be measured.
A field sobriety test for alcohol impairment works because alcohol-induced motor impairment is correlated with judgment impairment. If THC-induced motor impairment is not correlated, then a motor impairment test will be an inadequate field sobriety test.
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September 7, 2016 at 11:22 am
Exactly Grumble. So the part in the NPR report about designing better field tests is really important IMO. The kind of thing that points the finger squarely at next-priorities. If only legislators could see this….
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September 7, 2016 at 2:16 pm
@ dnadrinker – Regulators prefer objective tests to subjective, when available. It makes everyone’s life easier (except maybe lawyers).
@drugmonkey – I’m not sure how much legislators are/need to be involved. I know the FAA is working on these things, I assume NHTSA is as well.
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September 7, 2016 at 4:31 pm
Legislators are the ones that write laws that can determine how a ballot initiative law is actually put into practice. They decide how the tax revenues are spent. What regulatory commissions to set up and how they are to function, sometimes. They decide, in some states, whether or not to invest in State level funding for research topics.
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September 7, 2016 at 5:15 pm
DM – I understand, but as dnadrinker suggested, there are already laws in place that state that a person cannot drive/fly under the influence of illegal drugs. The US Congress has say in how the existing regulatory authorities spend their research money, but aside from earmarks, the regulatory agencies have a fair amount of flexibility on what specific lines to research.
I can see asking for Congress to spend more money researching marijuana detection, but I wouldn’t go so far as to suggest researching specific methods. IMO, Congress gets in trouble when they try to be too specific (e.g. earmarks based on politics, not science).
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September 7, 2016 at 11:32 pm
David, to be clear I am of the opinion that this is currently the responsibility* of the individual States that are legalizing recreational marijuana (and I point the finger at the States that already legalized medical marijuana as well). Not the Fed, they consider it all bogus and marijuana is just as Federally illegal as ever, save that Obama made it a very low priority for enforcing.
a person cannot drive/fly under the influence of illegal drugs.
emphasis added. mere detection that someone has been exposed to a nonzero amount of THC to the extent it shows up in bodily tissues is not the same thing as being “under the influence” when it comes to operating a motor vehicle. nor, necessarily, when it comes to occupational performance, another sticky civil rights issue that looms ahead.
*don’t get me wrong, I welcome Federal attention, I just think it is slightly more optional given the legal stance.
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September 8, 2016 at 11:03 am
Completely agree with your second paragraph. This has been a question in at least one court case I’m aware of for a pilot. Parts of the Fed may consider it bogus, but not the aviation side.
As for the first paragraph, my (cynical?) thought is that the only groups with the resources to fund the science are at the federal level.
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September 10, 2016 at 4:23 pm
How reliable are the tests for detection of THC use? what is the range.
I ask because of the endo system for this biochemicals, and you know there variations between people and ethnically different groups.
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September 12, 2016 at 1:16 pm
The accuracy of any given test (they can be quite accurate if done properly) is not the point. The point is that even a highly accurate determination of current blood THC load is unlikely to be a good indicator of driving impairment.
In contrast, blood alcohol level gives a much better indication of how recently the substance was ingested and (again better, not perfect) indicator of how impaired the driver is.
I am not aware of any ethnic differences in the endocannabinoid system that are as likely to be relevant to this issue as are the issues of naive versus chronic consumers and the ensuing implications for behavioral tolerance and sustained lower-level THC content in the body tissues.
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