Pesticide Residues Were Rare in Regulated Cannabis but Widespread in Illicit Canadian Samples
A 2023 study published in the Journal of Cannabis Research found a sharp difference in pesticide contamination between regulated and illicit cannabis in Canada. Researchers detected pesticide residues in two of 36 licensed samples—about 6%—compared with 22 of 24 illicit samples, or 92%.
The Health Canada researchers tested dried cannabis flowers collected in 2021. The licensed products were purchased through the Ontario Cannabis Store from producers representing all five Canadian regions. The illicit samples came from law-enforcement seizures submitted to Health Canada for laboratory analysis.
The laboratory method screened for 327 pesticide active ingredients using liquid- and gas-chromatography mass spectrometry. In the licensed products, the researchers found only trace amounts of myclobutanil and dichlobenil, each at the method’s lowest calibrated level of 0.01 micrograms per gram. Dichlobenil was not included on Canada’s list of 96 pesticide ingredients subject to mandatory cannabis testing at the time, illustrating why broader screening can identify contaminants that routine testing may miss.
The illicit samples showed a substantially different pattern. Researchers identified 23 pesticide active ingredients, with an average of 3.7 residues per sample. Myclobutanil, paclobutrazol and piperonyl butoxide were among the more frequently detected compounds, while chlorpyrifos, imidacloprid and myclobutanil reached concentrations far above the laboratory’s reporting threshold. One sample contained nine different pesticide ingredients.
The findings do not establish how exposure to the contaminated cannabis affected consumers, nor do they show that every illicit product is contaminated. The sample was small, and seized cannabis may not represent the entire illicit market. Even so, the contrast provides evidence that regulated products are subject to meaningful controls that are absent or difficult to verify in unlicensed supply chains.
Canada introduced mandatory pesticide testing for licensed cannabis on January 2, 2019. Under Health Canada’s testing requirements, licensed producers must demonstrate that cannabis has not been treated with or contaminated by unauthorized pest-control products before it can be sold.
The 2023 study also built on earlier Canadian testing that found unauthorized pesticide residues in more than 18% of licensed samples before the mandatory testing requirements took effect. The newer results suggest that contamination in the regulated market had become uncommon by the time of the 2021 sampling, although occasional trace findings show that surveillance remains necessary.
Subsequent government testing has pointed in the same direction. In a 2025 Health Canada comparison of 50 legal and 50 illegal dried-cannabis samples, only two legal products contained trace pesticide residues, while 47 illegal samples—94%—tested positive for pesticides and averaged 3.4 residues per sample. That later project also examined heavy metals, mycotoxins and microbial contaminants, providing a broader picture of quality differences between the two markets.
Together, the studies support the practical value of purchasing cannabis through regulated channels: licensed products are not guaranteed to be contaminant-free, but they are produced and tested within a system designed to detect and address unauthorized pesticide use.
