The Marijuana Potency Data

You may have heard a relatively sustained drumbeat in the mainstream press reports in the past few years regarding the content of current illicit cannabis products. It has been promulgated in a PR campaign which attempts to convince baby boomers that today’s marijuana is more dangerous than that of their own misbegotten youth because it is “stronger”. In other words, higher in the concentration of the major psychoactive constituent, Δ⁹-THC. The subtext, I assume, is to alleviate the boomer parents of today’s teens of any guilt related to communicating seemingly hypocritical anti-dope messages. If the pot today is more dangerous, then it is not hypocritical that Daddy and Mommy used to smoke in the seventies, right?
I have an objection to one of the fundamental concepts here* which explains my laziness in never bothering to track down the data on which the assertion rests. Happily, I stumbled across the relevant source.

Quarterly Report Potency Monitoring Project
Report 100 December 16, 2007 thru March 15, 2008
NIDA Contract Number: N01DA-5-7746, Mahmoud A. ElSohly, Ph.D.
[ http://www.whitehousedrugpolicy.gov/pdf/FullPotencyReports.pdf ]Browsing around the ONDCP site after yesterday’s comments, I ran across an interesting document that I hadn’t viewed before. It is the March 18, 2008 report from a NIDA contract that monitors the cannabinoid content of samples seized in law enforcement actions in the US.
I graphed the Δ⁹-THC data from Table 2 which reports the non-normalized cannabinoid averages of illicit cannabis samples by year seized. The report is methodologically light so I can’t figure out why the data are “non-normalized”, nor what normalizing procedures should be performed. Perhaps to account for site bias if they get more samples from one area of the country? Something like that. And who knows anything about the sensitivity of the assays for cannabinoids over time…we can assume there are comparable methods but it would be nice to see methods. (Surprisingly, I don’t immediately pull any relevant publications from the contract’s PI on Pubmed…) Anyway it seems likely that these are fairly raw analyses.
These are interesting trends. Reminds me of something…what was it….what was it… oh yes.
Remember this graph that I put up in a prior post on the efficacy of the War on Drugs?
These data report the annual prevalence for marijuana smoking in the Monitoring the Future survey. As we see in the left panel, there was an increasing trend from the mid seventies until the start of a sustained decline in the popularity of marijuana which started in the early eighties. This trend lasted until about the early nineties whereupon marijuana popularity started to increase again (I blame Snoop Dogg‘s release of The Chronic, myself :-)). [Update 11/24/08: Yeah yeah, commenters, it was released by Dr. Dre with significant contribution from Snoop that some would say launched his career. My bad. If you clicked through the link you would see this is made clear on Wikipedia.] Looking at the potency trends it is tempting to conclude that market forces influence the Δ⁹-THC content of the illicit marijuana supply, is it not?

return to huntSpeculation on illicit drug capitalism aside, I’m glad that I finally viewed the data on which the PR message rests. I have to admit that I’d been a bit skeptical about the basic claim over marijuana potency, just because of the generic suspicion (which many of my readers apparently share) that official anti-drug messages are sometimes a little free and easy with claims relative to the actual supporting data. I now have some framework on which to consider the assertions.
I didn’t work up the graph yet, maybe I will later, but Table 1 of the report has a breakdown of the number of seized marijuana samples which are in less-than 3%, 3-4.9%, 5-8.9% and 9%+ categories. This information will require a little more work (i.e. data entry from me) to make some sense but a quick glance will show you that the lower-concentration samples are more abundant. This should be taken into account when estimating content of the typical marijuana to which teens might be exposed.
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*My hesitation to credit the purported link between the Δ⁹-THC content in commonly available weed and increased risk is that smoked drugs of abuse tend to lend themselves to exquisite individual control over dosing. I’ll have to drag up some references eventually but there’s a whole literature in which it is shown that if you manipulate the nicotine content of cigarettes, smokers will alter their smoking topography (volume per puff, puff duration, etc) in the direction of restoring the dose obtained from their usual brand. The marijuana literature is smaller and hampered by the fact that the official NIDA-supplied (grown by El Sohly, the one who runs the analysis contract) marijuana tops out at about 3.6% Δ⁹-THC. Nevertheless a close reading of the available literature in controlled human laboratory studies will suggest that marijuana smokers are also quite good at titrating dose in response to the content of the smoked product.
Another way to put this is that users smoke to reach a subjective high rather than to consume a certain number of puffs of a certain amount of drug. The product and route of administration are such that the overdosing variance would seem to be quite narrow relative to cases where the drug administration is more of a one-shot ballistic event (like swallowing a purported Ecstasy pill of unknown content, IV administration of drugs of uncertain purity / weight). Consequently I tend to doubt that the concentration of the source material plays a huge role in establishing marijuana dependence.
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Update: 11/23/08: New readers (Thanks Andrew Sullivan!) may wish to read my prior posts on
Comparing Cannabis and Nicotine Withdrawal
and
“Legalize eet mon” the ongoing series: In which the “scientists” are blamed, yet again, for the failings of journalism.