Inter-Lab Variation within the Cannabis Industry

Inter-laboratory variation within the cannabis industry is a significant problem that not only reduces the public’s confidence in this industry but can also unknowingly lead to the sale and distribution of contaminated products.


Cannabis. Image Credit: HQuality/

Quality testing of cannabis products

Whether cannabis is fully legalized, as is the case in Canada, or partially legalized with a mixture of medicinal and recreational laws, as is the case in many parts of the United States, both quality control (QC) and quality assurance (QA) remain essential components of the cannabis industry. Whereas QC refers to the processes that ensure the quality of products, QA instead ensures the quality of the processes that are used to produce the cannabis products. It should be noted that illicit cannabis markets do not have any regulation or oversight pertaining to their quality, product safety, or their methods of production.

Typically, a cannabis product that has undergone QC/QA testing will be labeled as “Third Party Tested.” This label, therefore, informs the consumer that their cannabis product has undergone a series of laboratory testing, meets the industry standards, and also protects the producer from liability. In addition to adhering to these standards, laboratory testing of cannabis products is also important to ensure that these products are properly labeled. Some of the information that most consumers look for when purchasing cannabis products include their potency, terpene content, and the presence of any added ingredients.


Cannabis products are typically required to be tested for both their tetrahydrocannabinol (THC) and cannabidiol (CBD) potency, as these two cannabinoids are often sought after by consumers. Furthermore, knowing the potency of THC and CBD within a product can allow users to choose the best product for their needs.

For example, whereas many medicinal users will look for a cannabis strain with a high CBD: THC ratio, many recreational users will instead look for products with higher THC levels. Other cannabinoids that can also be considered for potency testing include CBDa, THCa, CBG, CBN, and CBC, many of which are of interest to medicinal users.

Within the United States, there is a lack of federal guidance on how the potency of cannabis-derived products is measured. As a result, laboratories across each state with legalized medicinal and/or recreational use of cannabis have had to develop and validate their own methods for measuring THC and CBD concentrations.

One common technique that is used to measure THC and CBD potency, as well as the concentrations of their acidic precursors tetrahydrocannabinolic acid (THCa) and cannabidiolic acid (CBDa), respectively, is high-performance liquid chromatography (HPLC). Knowing the presence of THCa and CBDa in a cannabis product is important, as these acids can degrade THC and CBD upon being heated through smoking or when being prepared for use in oil or edible products.

In short, the HPLC analysis of cannabis products begins with the extraction of cannabinoids from a dried plant through the use of various solvents. The residual fluid from this extraction will be fed into the HPLC system, which separates compounds based on the amount of time needed for them to pass through granular material.

Unfortunately, there is a lack of standardized methods available for determining THC and CBD potency, which has led to stark differences in potency measurements. The use of different solvents during the extraction period or different reagents during the HPLC analysis, for example, can cause variability to arise in the potency measurements.

Furthermore, the use of different instruments from different manufacturers, each of which comes with its own unique set of calibration requirements, can further contribute to this variability.


Pesticide contamination is also an important aspect of cannabis product testing, as cannabis, like many other products, can be exposed to certain pesticides, fungicides, and rodenticides while being grown to protect the plant from infestations. Myclobutanil is a commonly used pesticide by cannabis growers that are associated with causing reproductive toxicity in certain animal species. The potential toxicity of these pesticides is particularly important when cannabis products are used to make concentrates, as the extraction process for these products will lead to concentrated amounts of the pesticide as well.

The most common analytical techniques that are used to evaluate the presence of pesticides in cannabis products include gas chromatography-tandem mass spectrometry (GC-MS/MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). Unfortunately, there have been several reports of inter-laboratory variation in pesticide contamination levels in cannabis products.

One recent study aimed to confirm this variability by submitting a set of cannabis distillate samples that were known to be pesticide-free with a set of samples spiked with known amounts of six pesticides to five different laboratories in the central California area.

As regulated by the state of California, the samples in this study were analyzed for the presence of 66 different pesticides. For the pesticide-free samples, all five laboratories successfully reported that no pesticides were detected, thereby achieving a false positive rate of 0%.

Comparatively, although myclobutanil levels in the known cannabis sample were above that which is allowed by the state of California, only five of the 10 samples were found to be positive for this pesticide. While two of the laboratories did not report any myclobutanil to be present in these samples, those that did confirm the presence of myclobutanil found the levels to closely resemble the known values.

Another pesticide that was added to the known samples was paclobutrazol, which is not allowed in any detectable amount in cannabis products by the state of California. Unfortunately, all five laboratories in this study claimed that the cannabis samples were negative for the presence of this pesticide, even though the researchers added a known amount of this pesticide, which was over the limit of detection (LOD), to their samples.


The inter-lab variability that exists within the cannabis industry is concerning, particularly when contaminants like pesticides are being underreported by these analytical techniques. One potential resolution to this problem is the establishment of standardized federal regulations, such as those which exist in the testing of food products, to ensure that laboratories can adequately confirm the safety of cannabis products.


Further Reading

Last Updated: Aug 2, 2021

Benedette Cuffari

Written by

Benedette Cuffari

After completing her Bachelor of Science in Toxicology with two minors in Spanish and Chemistry in 2016, Benedette continued her studies to complete her Master of Science in Toxicology in May of 2018. During graduate school, Benedette investigated the dermatotoxicity of mechlorethamine and bendamustine; two nitrogen mustard alkylating agents that are used in anticancer therapy.


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