Medical Research News

Tainted CBD Impedes Pharmacological Use

Written by Lydia Kariuki

The Brightfield Group estimates that the global cannabidiol (CBD) market in 2020 is poised to increase by 14% from last year’s sales which stood at $4.1 billion. Economic constraints brought by the global pandemic and other compounding factors have hampered market growth, but the positive CAGR (compound annual growth rate) is encouraging.

One recent review by Colorado State University–Pueblo summarized ways that cannabis products may be contaminated, such as pesticides and heavy metals, but also pointed to plant growth regulators and polycyclic aromatic hydrocarbons. [1] These pollutants pose risks to the health of immune-compromised patients and pediatrics.

State-legal cannabis products require testing for many contaminants. While one could argue that not enough product is tested per batch, most regulators would likely agree that state-legal cannabis is more heavily tested and regulated than many other everyday products. Some contaminants outlined in the review, however, may not be currently tested by 3rd-party labs.

The hemp industry is not so regulated outside of the levels of delta-9-tetrahydrocannabinol (THC). The review highlighted inaccuracies in labeling THC and CBD levels as well as contamination by microbes, heavy metals, and pesticides.

This study also highlighted case studies that describe cannabis contamination and the medical consequences that manifest. Four categories were considered, including labelling inaccuracies, microbes, heavy metals, and pesticides.

Labeling Inaccuracy

Inaccurate labelling of THC content may pose risks to pediatric patients especially regarding brain development. [2] Inaccurate labelling of cannabinoids may also be misleading to medicinal cannabis patients. The researched expressed the need to include minor phytocannabinoids in the labelling requirements, such as cannabigerol (CBG).

Microbial Contamination

Fungal contaminants pose the highest risk for microbial contamination in cannabis. Penicillium sp. and Aspergillus sp. have been linked to the production of aflatoxins while Fusarium has been shown to produce other mycotoxins like fumonisin. [3, 4] These toxins have carcinogenic potential. [5]

No reports were shown of bacterial or viral infections in humans caused by cannabis. Potentially dangerous bacteria include E. coli, Salmonella, and Clostridium.

Heavy Metal Contamination

Heavy metal contamination is common in cannabis. The metals involved include cadmium, copper, magnesium, lead, and mercury. [6]  When they accumulate in the body over time, these heavy metals pose significant health risks.

Pesticide Contamination

Insecticides, fungicides, and plant growth regulators are commonly used in the cultivation of hemp and cannabis. Unfortunately, there are no universal guidelines as to how pesticides should (or should not) be used for cannabis or hemp. For example, in 2016, hazardous pesticides like abamectin that are used on ornamental plants were found in about 49% of Cannabis samples that were obtained from California dispensaries. [6] Pesticides advertised as all-natural ingredients like cinnamon oil actually contained abamectin. A whopping 84% of samples (n=26) tested from Washington state dispensaries contained a cocktail of insecticides, miticides, fungicides, insecticidal synergists, and plant growth regulators. [7]

With this background, the authors recommended that testing requirements for cannabis be standardized and that a more comprehensive understanding of cannabis contamination be undertaken. This goal is to guarantee patient and consumer safety. [1]

Image Source: KTrimble, CC BY-SA 3.0


  1. Montoya Z, et al. Cannabis contaminants limit pharmacological use of cannabidiol. Frontiers in Pharmacology. 2020;11(571832). Times Cited: n/a, Journal Impact Factor: 3.860
  2. Gruber SA, et al. Worth the wait: effects of age of onset of marijuana use on white matter and impulsivity. Psychopharmacology. 2014;231:1455–1465. Times Cited: 54 (PubMed), Journal Impact Factor: 3.130
  3. Daley P, Lampach D, Sguerra S. Testing cannabis for contaminants. Woodlands Hills, CA: BOTEC Analysis Corporation; 2013. Times Cited: n/a, Journal Impact Factor: N/A
  4. Punja ZK, et al. Pathogens and molds affecting production and quality of Cannabis sativa L. Front Plant Sci. 2019;10(1120). Times Cited: 4 (PubMed), Journal Impact Factor: 4.402
  5. Pitt JI, Basi´Lico JC, Abarca ML, Lopez C. Mycotoxins and toxigenic fungi. Med Mycol. 2000;38(1):41–46. Times Cited: 18, Journal Impact Factor: 2.851
  6. McPartland JM, McKernan KJ. Contaminants of concern in cannabis: microbes, heavy metals and pesticides. In: Chandra S, Lata H, & Elsohly MA, eds. Cannabis sativa L. – Botany and Biotechnology. Springer International Publishing; 2017: 457–474. Times Cited: 21 (Semantic Scholar), Journal Impact Factor: n/a
  7. Russo EB. Current therapeutic cannabis controversies and clinical trial design issues. Front Pharmacol. 2016;7:309. Times Cited: 57 (Semantic Scholar), Journal Impact Factor: 3.860

About the author

Lydia Kariuki

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