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The Accuracy Question
IN 2008, with backing from Harborside Health Center, grower/entrepreneurs David Lampach and Addison DeMoura got trained by an analytic chemist in the art/technique of gas chromatography/mass spectrometry so that they could test Cannabis buds for cannabinoid content. They contracted with a microbiology lab to assess the buds' mold content. And by 2009 director Steve DeAngelo could assert that the herb on sale at Harborside had been deemed safe with respect to Aspergillus and other pathogens, and labeled as to THC and CBD content.
Labs run by experienced chemists soon entered the field, some employing liquid chromatography and other analytic techniques. As of this writing we know of 10 PC labs (PC as in "Pro-Cannabis"), with several others getting ready to launch. Steep Hill remains dominant in terms of sales and competitive in terms of technology.
"The labs will effectively audit one another for accuracy," said Dale Gieringer of Caifornia NORML a few months ago. "Any pattern of discrepancies will eventually become apparent." Gieringer has decided to expedite "eventually" by conducting an audit. He'll be submitting identical samples to all the analytic labs -using a front person, of course- and analyzing the results, which will be reported here and at CaNORML.org.
How Accurate are the Labs' Numbers?
When a dispensary displays the cannabinoid content of buds or other products they're selling, there is a misleading implication of pinpoint accuracy. The weak link here, according to sources we trust, is the use of questionable standards. A chemical "standard" is utilized as a benchmark, to which an unknown sample is compared, so that a precise content of a given component can be ascertained. An inaccurate standard will skew results.
Commercially available cannabinoid standards are not necessarily reliable, we were surprised to learn. If a testing lab bases its calculations on THC or CBD in methanol purchased from a chemical supply house, and the amount present is less than claimed, a serious over-estimation of cannabinoid potency results.
CBD can be crystallized, so it is practical for a lab to create its own 100% pure CBD reference standard. With THC, a tarry, viscous liquid that sticks to glassware and everything else, it is much more difficult to create an accurate standard.
Sampling is also a weak link. From a pound of buds typically delivered by a grower in a turkey bag, the dispensary chooses a few -say, two grams' worth- to send to the lab. Since location on the plant is a factor in cannabinoid production, if two of the three sample buds are from cola tops, they won't provide a true average for the plant as a whole.
European researchers question the likelihood of growers producing buds containing more than 30% THC by weight. We know that state-of-the-art hashish from the best genetics tops out around 50-60% THC (Clarke 1998; Mehmedic, Chandra et al. 2010), which should be comparable to the highest calculated THC content in a trichome. Now, look at photomicrograph of a whole bud. What percentage of a bud do you think is composed of the glandular trichome heads themselves?
Let's just say 33% by weight, which may even be a high estimate. [Also present in the trichome are terpenoids, flavonoids, water, squalene, and waxy ballast from the cell walls.] Then 33% of 60% THC in a trichome head should be 20% THC. In fact, that would seem to be a very good benchmark. GW Pharmaceuticals, after years of selective genetic breeding, and advanced research on optimizing cultivation and environmental control techniques produces material with a consistent THC yield in this range (Potter 2004). Documented THC levels above 20% are quite rare, even for sinsemilla (Mehmedic, Chandra et al. 2010). We are not saying "impossible," but "quite rare."
Although high numbers might be a selling point from the dispensary's point of view, and a 25% THC bud or product might seem much more desirable than 15% THC, the patient would get the same medical effect from the latter by taking an extra vaporizer inhalation or nibble of a cookie (assuming the proper accompanying terpenoids are present). Adjusting intake to achieve the desired effect is what titration is all about.
The pharmacological importance of terpenoids has been stressed by some perspicacious researchers (McPartland and Russo 2001; Fischedick, Hazekamp et al. 2010). Patients who abandon a suitable strain for one with higher THC and/or CBD content may not be getting more relief for their money if the terpenoid profile is significantly different.
There is solid science available in the literature on Cannabis components and their proper analysis.
Clarke, R. C. (2010). Hashish! Los Angeles, CA, Red Eye Press.
Fischedick, J. T., A. Hazekamp, et al. (2010). "Metabolic fingerprinting of Cannabis sativa L., cannabinoids and terpenoids for chemotaxonomic and drug standardization purposes." Phytochemistry 71(17-18): 2058-73.
McPartland, J. M. and E. B. Russo (2001). "Cannabis and cannabis extracts: Greater than the sum of their parts?" Journal of Cannabis Therapeutics 1(3-4): 103-132.
Mehmedic, Z., S. Chandra, et al. (2010). "Potency trends of delta(9)-THC and other cannabinoids in confiscated cannabis preparations from 1993 to 2008." Journal of Forensic Sciences.
Potter, D. (2004). Growth and morphology of medicinal cannabis. Medicinal uses of cannabis and cannabinoids. G. W. Guy, B. A. Whittle and P. Robson. London, Pharmaceutical Press: 17-54.
A Realistic Perspective on Lab Tests
Raber on the CBD "Appearance Rate"