Wednesday, November 26, 2008

Detecting cannabis intoxicated drivers

One of the important features of an effective drug control policy is the ability to detect drivers who are actually impaired by a drug. We can confidently distribute alcohol to the universe of adults because we can punish those who misuse alcohol by driving while impaired by alcohol.

Purdue University issued a press release in August 2008 that said that Purdue personnel and a business were forming a new business (Intelimmune LLC) to detect the actual presence of THC in the body. We all know that there is a very big space between a press release about the intent to do something that involves scientific research, peer review publication, product engineering, testing and approval of the scientific instrument, successful marketing, and actual use on the street. This is still a ways out.

But we should wish them Godspeed. An accurate measure of impairment linked directly to the neurologically active quantity of THC, and other relevant cannabinoids, would be an important feature in building public acceptance of legal, responsible cannabis use.

Accurate measures of alcohol ingestion correlated to measures of impairment means that our society is comfortable allowing Americans to consume alcohol, because we are a society that travels by car. We have an objective tool to discriminate between those whose drinking has not degraded their ability to drive a car below a minimum standard, and those whose drinking has done so. Implicit in this policy is the belief that there is a fairly standard correlation between quantity detectable in the blood and the degree of impairment. (Whether there is a similar curve for cannabis ingestion and the ability to operate an automobile is something we have yet to learn.)

The key point is that our society recognizes that many people drink modestly and then drive at some point thereafter, and we can sort out those whose drinking has been too great to permit them to be driving.

Effective drug policy requires accommodating this reality for other drugs too. The self-controlled social use of cannabis and other drugs will include mobility. It would be unrealistic to think that a legal cannabis policy would require that no one could drive for, let's say, twelve hours after ingesting cannabis.

A critical element of obtaining law enforcement buy-in, insurance company buy-in, auto safety advocate buy-in -- indeed buy-in by anyone who is not a cannabis user who also uses the roads, that is everybody -- is accurate impairment testing.

Impairment testing can either be performance based or based on a measure of drug quantity that has been tied experimentally to driver performance. Direct performance testing is the highest, most logical standard, as it applies to ability to drive regardless of the cause of impairment: tiredness, use of over-the-counter cough, cold or allergy medication, other legal medication, age, disease, etc. We use the much more subjective approach of the field test by the side of the road of performance impairment: reciting the alphabet backwards, and physical tests such as touching one's nose with a finger or testing balance by walking in an unusual manner (i.e., heel to toe).

Our society believes that there is a direct correlation between the blood alcohol concentration (BAC) and impairment. We believe that this is sufficiently true in order to impose criminal liability for driving while impaired based upon the evidence of the BAC. We believe that the instruments used to measure BAC -- such as the Breathalyzer that "estimates" the BAC based upon the alcohol concentration in exhaled air -- are sufficiently accurate that we consider this evidence to be "objective" and more reliable than the visual field test of a police officer.
Currently, there is a consensus in our society and the courts that the "objective" approach to detect alcohol-induced impairment the relies upon the blood alcohol concentration standard is satisfactory. It may be that lawyers and scientists will challenge this consensus.

To the extent our society remains committed to this kind of "objective" measure, the Intelimmune concept sounds like it is taking the science in the right direction.

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1 comment:

Anonymous said...

Police do not ask people to say the alphabet backward. Most people can not do this sober. They ask people to say the alphabet forward. Often a highly drunk person will make errors when attempting this.