How Accurate Is Cannabis Testing? Ring Test Assesses Labs


The Weed Blog

Mixed Findings Show Strengths and Problems Among Analytic Testing Services

How accurate is cannabis potency testing? California NORML and Project CBD have released the results of their first “Ring Test” to assess the accuracy of analytical laboratories.
In the winter of 2010-2011, California NORML and Project CBD initiated a “Ring Test” to assess the accuracy of the numerous analytical cannabis testing laboratories that have recently emerged to serve medical marijuana dispensaries, breeders, growers and patients.
Results of the study, coauthored by California NORML Director Dale Gieringer and Dutch scientist Dr. Arno Hazekamp, are reported in the Autumn 2011 issue of O’Shaughnessy’s, the Journal of Cannabis In Clinical Practice [PDF].

Dale Gieringer, California NORML: “We wanted to know how reliable is the information provided by analytical cannabis labs?”

​”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,” Gieringer said. “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 analyses.
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

In most cases, lab results were consistent within plus or minus 20 percent on replicate samples (and often within 10 percent).
For example, a sample with 10 percent average THC content might range from 8 percent to 12 percent in different tests. This is similar to the accuracy of the government’s potency testing program run by the National Institute on Drug Abuse (NIDA) lab at The University of Mississippi, as well as comparable government-regulated industries such as environmental testing.
The researchers concluded that the precision and proficiency of a majority of cannabis testing labs compared favorably to other analytical testing industries.


​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 percent from the mean. Three of the 10 labs performed unacceptably on half the tests.
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.
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. Both GC and LC instrumentation should be considered reliable for cannabis potency analysis, according to the researchers.
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.
More work is required to assess the accuracy of current methods for testing cannabis tinctures, edibles and other extracts, according to the study.
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 percent variation observed.
Labs should reevaluate the precision level at which results are reported, the study concluded.
“Customers are well advised to check out a lab’s professional credentials and references, and to ask some tough questions before they decide to work with a given lab,” the study concludes.
The Project CBC/CA NORML Ring Test report is accompanied by a list of 10 questions (reproduced above) that patients and providers might want to ask when choosing to work with an analytical testing lab.
“Analytical labs provide an important service for the medical marijuana community,” said 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,” Russo said.
“[A] paid service such as potency-testing should deliver what it promises: accurate results that lead to a better understanding of an important and potent medicine,” the study’s authors conclude. “We plan to organize a wider range of ring tests in the near future to help keeping the testing industry sharp, and to guarantee that patients will get what they deserve: high quality and safe medicinal cannabis.”