The Basics of Cannabis QC

Every year cannabis for medical and recreational use becomes legal in more places throughout the United States. As of 2017, 29 states and the District of Columbia (DC) have passed laws to legalize growth and distribution of the plant. Cannabis is not federally regulated in the U.S. which means states opting for legalization must adopt regulations to ensure patient and user safety. This can leaf laboratories wondering how to satisfy regulatory requirements for cannabis products.

Cannabis QC Best Practices

Just like any other laboratory, priority number one for laboratories testing cannabis is to ensure the quality of the product. Best practices for cannabis quality control include:

  1. Validating methods
  2. Using proper controls
  3. Monitoring processes to prove they are working correctly
  4. Verifying technicians can effectively perform test methods by conducting routine proficiency testing (PT)

What’s lying in wait in your weed?

Laboratories are responsible for conducting tests to detect microbial impurities in cannabis. Interestingly, what is considered a “microbial impurity” differs from state to state. Some state regulations call out specific strains that cannot be present in a cannabis product, while others are more general. Although regulations vary, the top three microbial impurities all labs must test for are:

  • Yeast and mold (aflatoxin producing)
  • Shiga toxin-producing Escherichia coli (STEC)
  • Salmonella

For example, the Bureau of Marijuana Control California Code of Regulations Title 16, Division 42 Section 5316 and the Colorado Department of Health call out specific impurities including STEC, Salmonella, Aspergillus fumigatus, Aspergillus flavus, Aspergillus nigerAspergillus terreus.

Interpreting and Implementing Regulations

Every state that legalizes cannabis creates regulations stating laboratories must test and find impurities, but not all require laboratories to test for the absence of these impurities. Colorado’s regulations offer some of the most straightforward guidance. To find out how testing laboratories interpret regulations and test for impurities, I conducted an interview with a contract cannabis testing laboratory in Boulder, Colorado. Below are examples of testing methods they use to meet the requirements of Colorado regulations:

  • Yeast and mold are tested using manual methods
    • Sample matrices are spiked with an enumerated culture of yeast, homogenized and plated
    • The inoculum is run in parallel to calculate the percent recovery of yeast in the matrix
  • STEC and Salmonella are tested using molecular methods
    • Sample matrices are spiked and enriched overnight
    • The enriched samples are then tested for E. coli and Salmonella using qPCR
    • In-house developed assays or commercial test kits are available for working with a cannabis matrix and PCR
  • Each test is run with controls almost daily to prove to auditors that the methods effectively detected the presence/absence of sample impurities

This is just one example of the many methods used for detecting microbial impurities in cannabis products.  Although the methods and regulations are not harmonized, all testing laboratories share a common goal: to ensure product quality and patient safety.

Microbiologics provides the microbial controls and proficiency testing solutions your laboratory needs to maintain the highest quality standards. Choose from common proficiency testing panels or partner with us to create customized testing solutions. Visit to learn more.



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