Stewart, Ward Jr and the forensic toxicology of weed.

On the evening of August 9th, 2014, an altercation on Canandaigua Motor Speedway’s muddy track resulted in the death of a 20 year old racer. The heavy metal I grew up watching; the mud, blood and dirt of of a small track speedway; the testosterone that drives so much of it’s checkered past and dominates it’s present. All of it met that night, to deadly effect. Last week, the Livingston County prosecutors, in acquitting Tony Stewart of all charges, charged that Kevin Ward, Jr may have had enough marijuana in his system to have impaired his judgement.

Common knowledge has it that marijuana stays in your system up to two months at testable levels. How then could a forensic test determine that Ward, Jr was high at the moment of his untimely end? Or is that just more prosecutorial flourish than fact?

The biology of pot metabolism.

To begin with, we need to understand a bit of the basics of how cannabis is metabolized – or broken down – by the body. There are essentially two major phases of this process which create two distinct metabolites: hydroxy-THC and carboxy-THC.

The first phase of metabolization takes the raw THC that the subject smoked, ate or otherwise consumed and creates hydroxy-THC (THC-OH). Basically, the body takes the THC molecule and sticks a hydroxyl group on to one side – a pair of oxygen and hydrogen (OH). This is a relatively swift process, taking an estimated 4-6 hours to complete. hydroxy-THC is not a psychoactive drug any longer, however, some studies have suggested that the “munchies” happen a few hours after smoking pot specifically because of the break down of this particular metabolite into…

Carboxy-THC (THC-COOH) is the next phase of metabolism. At this point, the body has added a carbon and another oxygen to the original pair, creating what is known as a “Carboxyl Group,” or COOH. Carboxy-THC is an inactive chemical, pharmacologically speaking, and more or less the end of the road of anything that looks like THC. But this is one of the chemicals that drug tests that you might take for pre-employment screening test for. This is the one that lasts two, three or more months in the body.

What does this mean for testing?

Because there are two distinct metabolites – and because one has a lifecycle of only 6 or so hours – it is possible to at least determine within a range of hours how recently a person smoked pot. And based on a comparison of the amount of hydroxy- and carboxy-THC it is even possible to determine just how high someone might have been at the time of death.

But there are caveats, and they’re important ones.

First, as with all toxicology reporting, a person’s height, weight, body mass index and general health all play in as factors in determining how quickly the body can break down hydroxy-THC. Also, because hydroxy- becomes carboxy-THC and a heavy smoker can be assumed to have high levels of carboxy-THC, frequent pot smokers are going to take longer than infrequent smokers to break down the hydroxy-THC.

All of these factors make determining exact amounts or times more or less impossible. For this reason, similar toxicology reporting has been either thrown out of court or else disregarded by juries. There are enough questions surrounding this type of test that prosecutors have so far had a difficult time convicting people based on this type of evidence.

In this case, however, forensic investigators have one major point in their favour, in that Kevin Ward, Jr is unfortunately dead. Convicting a living person of driving while intoxicated is hard, at least in part because somewhere between arrest and blood testing, hours may have passed. It’s just too easy to explain away a window of 4 to 6 hours.

But when a person dies, the metabolic clock stops. We can safely say that a person died at a specific time, and working back from there, we can compare the hydroxy- and carboxy-THC levels in the body and say that Kevin Ward, Jr was or was not high within a reasonable doubt. Thus based on the evidence I’ve been able to gather, it is at least a possibility that the prosecution’s contention in this case is based on solid evidence.

I attempted to contact quite a few forensics experts on this subject, but sadly, could not get a response in time for this article to be published.