Planes, Trains and Automobiles: Operating While Stoned

ptauto1The circus was in town (Washington DC) July 31, 2014. The House Oversight and Government Reform Subcommittee on Government Operations held a hearing entitled, “Planes, Trains and Automobiles: Operating While Stoned,” chaired by Rep. John Mica, R-Fla., and starring Rep Gerry Connolly, D-Va.

The committee didn’t get the answers they wanted from the capable testifiers, in large part because they asked the wrong questions. Both congressmen persist in the common belief that marijuana is like alcohol, and that there should be a magic number of Δ9THC in a driver’s blood that will prove they are too impaired to drive safely.

We need to remember that blood is never impaired, regardless of the level of intoxicants that may be in it. Only the brain is impaired by intoxicants. Testing the blood for drug content is simply a convenient surrogate for what’s in the brain. Autopsies have shown that there can be a wide difference between THC in the brain and THC in the blood. Usually, the THC content in the brain is higher than that in the blood. That makes finding a “magic number” in the blood that equates to impairment unrealistic, even if we weren’t faced with the high degree of variability in sensitivity to THC from one individual to the next. The inter-person variability in response to marijuana is estimated to be at least five times the variability seen with alcohol.

bloodsampleThe time between an incident (arrest, crash, vehicular homicide, etc.) and taking a blood sample is so long (typically over two hours) that the resulting drug level in the blood is a very unreliable indicator of what the drug level was at the time of the observed infraction.

Those who wait for “science” to determine an appropriate level, need to remember that “science” never arrived at a .08 gm/dl level for alcohol. That level was not established by “science”, but by courageous politicians, based upon input from scientists. Other countries have per se levels for alcohol ranging from .02 to .10 gm/dl – and all are based on the same science! This is to be expected when science guides policy decisions that are ultimately made by politicians.

These are some of the reasons why experts say there is no “magic number,” and never will be. It’s not because we need more research. It’s because of human biology.

The science is complex and rife with mischaracterizations by both alarmists and the marijuana lobby. It’s no wonder that little light was shed on the topic during a 1:42 congressional hearing.

Rep. Mica did get one thing right, at least. He showed a roadside oral fluid-testing device used in other countries that needs to be widely used here as well. These devices test for a range of drugs, not just marijuana. This is critical, because even though marijuana-impaired driving is hogging the spotlight, the real problem isn’t marijuana-impaired driving, but rather, drug-impaired driving. Marijuana-impaired driving is a subset of the real problem which is primarily a poly-drug and drug plus alcohol problem.


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