- The Weed Blog https://www.theweedblog.com

How Accurate Is Cannabis Lab Testing?


cannabis scienceCalifornia NORML and Project CBD release the results of the first “Ring Test” to assess the accuracy of analytical laboratories

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 the numerous analytical cannabis testing laboratories that have recently emerged to serve medical marijuana collectives, breeders, growers and patients.

Results of the study, which was 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 on pages 17-18, posted at: http://www.canorml.org/RingTestOShaughnessys_Aut11.pdf

“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

o In most cases, lab results were consistent to within plus or minus 20% 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 an 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.”

For more information contact: Dale Gieringer at California NORML — 510-540-1066 dale@canorml.org or Project CBD — 707-581-1818, info@projectcbd.com

Release by: California NORML


About Author


  1. This is a key point from this article: 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. 

  2. Our government needs to listen to the people. “People should not be afraid of their governments. Governments should be afraid of their people.”

  3. Michael Hennigan on

    If you are going to We The People to sign petitions, please sign mine cuz I have no friends! Mine says…close 50% of our overseas military bases and bring those Americans home. They have jobs but will need housing. Spend our defense money here in the U.S…. thats it! the address is http://wh.gov/gv5 Also sign all the MJ ones! At the time of this writing I only have 12 signatures!

  4. If I’m not mistaken there are three diferent ways they can use to test for THC in the system,one is the usual litmus papertsts which is definitely not dependable by any means,then the other is yb using a gas whatever,anyways it’s suppose to detect how much THC is in the system but it also has it’s down sides,I can’t remeber what the last one is or how it works.The point is that none of them are really all reliable as many other substances can show up positive.Diferent foods can and as my doctor informed me,I take a lot of meds from oain to tranqs and sedatives to a few others.Anywya’s kile he told me.Say lets use what I have to take.There have never ever been any testing or research as to how the combination of any of these meds react insofar as showing up as a positive hit for THC even though I may not have used it.So you have to ak you’rselves how amny people out there who have to take diferent combos of medications are tested and come uo positive only because there has never been any teasting and or research to show how they interact with each other and therefore can caue a persons drug test to come up positive even though they havn’t used marijuana.Pretty messed up isnt it?All the same it’s the truth

  5. We the People petitions at the Whitehouse –
    Sign the petition to “Legalize and Regulate Marijuana in a Manner Similar to Alcohol.” at

    Repeal any and all laws pertaining to the illegalization of the Cannabis plant and all of its uses http://wh.gov/gK2

    Allow United States Disabled Military Veterans access to medical marijuana to treat their PTSD http://wh.gov/4xd

    End the destructive, wasteful and counterproductive “War on Drugs” sign it at http://wh.gov/g0S

    Petition to “Legalize, regulate, and tax marijuana.” at


    Petition to “Stop Interfering With State Marijuana Legalization Efforts” at



    Petition to “low Industrial Hemp to be Grown in the U.S. Once Again” at


    Tell your Congressional Representatives –
    It is time to “Change the Schedule of Cannabis, Cannabis Laws, and Drug Czar Laws”
    Read and Sign the petition at

Leave A Reply