How Accurate Is Cannabis Potency Testing?
Cal NORML Release - Sep 21, 2011
Mixed findings show strengths and problems among analytic testing services
In the winter of 2010/11, California NORML and Project CBD initiated a “Ring Test” to assess the accuracy of analytical cannabis testing laboratories that have recently emerged to serve medical marijuana collectives, breeders, growers and patients.
Coauthored by California NORML director Dale Gieringer and Dutch chemist Dr. Arno Hazekamp, the full results of the Ring Test are reported in the Autumn 2011 issue of O’Shaughnessy’s, the Journal of Cannabis in Clinical Practice.
“We embarked on a parallel study of cannabis testing labs to shed light on a significant, unresolved issue within the fledgling medical marijuana industry in California and other states,” says Gieringer, “We wanted to know how reliable is the information provided by analytical cannabis labs? Are they adequately serving the needs of medical marijuana patients and providers?”
Ten cannabis labs in two states agreed to participate in an anonymous, side-by-side study to assess the accuracy and precision of their collective work. The participating labs employed a variety of analytical techniques and instrumentation to conduct their analysis. Six samples drawn from the same sources were tested by each lab: four herbal samples, including one CBD-rich strain, and two tinctures (alcohol extracts).
Results of the Ring Test indicate the following:
o In most cases, lab results were consistent to within plus or minus 20% of each other on replicate samples (and often within 10%). For example, a sample with 10% average THC content might range from 8% to 12% in different tests. This is similar to the accuracy of the government's potency testing program run by NIDA's lab in Mississippi, as well as comparable government-regulated industries such as environmental testing. Conclusion: The precision and proficiency of a majority of cannabis testing labs compared favorably to other analytical testing industries.
o While a majority of labs performed within acceptable limits, some reported results that deviated substantially from the average, with unacceptable deviations of more than 25% from the mean. Three of the ten labs performed unacceptably on half of the tests. Conclusion: Not all cannabis testing labs are performing up to par; consumers are well advised to check the reputations and professional experience of labs they work with, and to arrange backup tests from more than one lab where accuracy is essential.
o Both gas chromatography (GC) and liquid chromatography (LC) instrumentation yielded accurate results in testing of raw cannabis samples, with comparable and acceptable repeatability for identical samples. Conclusion: Both GC and LC instrumentation should be considered reliable for cannabis potency analysis.
o In the case of the tinctures (alcohol extracts), there were significant discrepancies in the results found by different labs, with GC generally reporting significantly higher potencies than LC . This made it impossible to reliably estimate the actual potency of the original samples. Conclusion: More work is required to assess the accuracy of current methods for testing cannabis tinctures, edibles and other extracts.
o No analytical testing lab demonstrated precision that supports reporting cannabinoid results to two decimal places. By unnecessarily reporting results to the one-hundredth percentile, some labs created an unrealistic illusion of precision that raises false expectations regarding the degree to which accuracy is possible, given the 20% variation observed. Conclusion: Labs should re-evaluate the precision level at which results are reported.
The Project CBD / CA NORML Ring Test report is accompanied by a list of ten questions that patents and providers might want to ask when choosing to work with an analytical testing lab.
“Analytical labs provide and important service for the medical marijuana community,” says Sarah Russo, Project CBD’s outreach coordinator. “We hope that cannabis labs, while competing for market share, will cooperate to improve their methods and maintain a high performance standard. Medical marijuana patients and providers would be well served by labs that share information and assist each other in a collegial manner.”