Cannabis testing is critical for consumer safety—but it’s also remarkably complex. Seltenrich  explains that states in the US “have come up with widely varying responses” to the challenge given an absolute lack of federal guidance. Furthermore, as Craven et al  point out, “guidelines have been set by different countries…” The practical result is that analytical laboratories are left to navigate this puzzle based on their precise geographic jurisdiction.  Consumers are subject to huge variations in product testing and quality.
Tested contaminants generally include some combination of pesticides and fungicides, heavy metals, molds and their toxins, microbes, solvents, moisture, and foreign matter. [1-4] Potency reports that quantify cannabinoids and terpenes may also be required. [3,4]
An additional variable regards the form of the cannabis product; for example, inhalable cannabis differs significantly from oral cannabis in terms of potential health consequences. Edible cannabis infusions may require homogeneity testing to avoid variable doses in a single product. [4,5]
California is among the strictest testing environments in the US with a list of 66 pesticides regulated at lower levels than other agricultural goods.  In fact, complaints of testing failure have surfaced among Californian farmers who avoided using any pesticides. Oregon comes close with 59 required pesticide tests. 
By comparison, Washington and Colorado require a total of 13 pesticides to be tested. Several of the 13 are identical, but others are not. Furthermore, Colorado does not require that concentrates be tested for pesticides—only flower. Residual limits also vary by region. [1,2] Some states, such as Florida, don’t explicitly require any pesticide testing. Canada trumps all US states with a list of 96 pesticides. To clarify, that’s 30 additional pesticides compared to the ‘strictest’ US state. Confused yet? This is only the tip of a deep iceberg.
Back to California: residual solvent limits for butane (common solvent) is set at 5,000 ppm. But in Colorado, presumably a less strict state, the limit is 1,000 ppm. In Massachusetts, the interim limits for butane and propane were set at 1 ppm!
Another example—and they are almost endless—Pennsylvania and Oregon enforce a moisture limit of 15%. However, the Dutch-based Office of Medicinal Cannabis sets the limit at 5-10%, which is supported by the Association of Public Health Laboratories. The United States Department of Agriculture suggests a maximum moisture content of 12% for hemp. Method requirements also vary widely. Valdes-Donoso et al  explain that “Some states…require more sophisticated and costly wet-lab tests for pesticides and heavy metals.”
Ultimately, cannabis testing is currently a mess of arbitrary, patchwork regulations. Relying on science to develop trustworthy standards can help ensure the health and safety of consumers and especially patients.
- Nate S. Cannabis contaminants: Regulating solvents, microbes, and metals in legal weed. Environ Health Perspect. 2020;127(8):82001. doi:10.1289/EHP5785. [Impact Factor: 8.05; Times Cited: 2]
- Craven CB, et al. Pesticides and trace elements in cannabis: Analytical and environmental challenges and opportunities. J Environ Sci. 2019;85:82-93. doi:https://doi.org/10.1016/j.jes.2019.04.028. [Impact Factor: 2.037; Times Cited: 5]
- Nie B, et al. The role of mass spectrometry in the cannabis industry. J Am Soc Mass Spectrom. 2019;30(5):719-730. doi:10.1007/s13361-019-02164-z. [Impact Factor: 3.202; Times Cited: 10]
- Valdes-Donoso P, et al. Costs of cannabis testing compliance: Assessing mandatory testing in the California cannabis market. PLOS ONE, 2020;15(4): e0232041.doi:10.1371/journal.pone.0232041. [Impact Factor: 2.740; Times Cited: n/a]
- Blake A, Nahtigal I. The evolving landscape of cannabis edibles. Curr Opin Food Sci. 2019;28:25-31. doi:https://doi.org/10.1016/j.cofs.2019.03.009. [Impact Factor: 3.828; Times Cited: 4]