Pyrethrins are a class of natural terpenoid pesticides produced by Tanacetum cinerariifolium, commonly known as chrysanthemum. Here we present evidence that cannabis may be able to produce pyrethrins endogenously. Flower from a cannabis plant grown in a closed hydroponic environment contained 2.48 parts per million pyrethrin I by weight. A comparison of the genetics of T. cinerariifolium and Cannabis demonstrates Cannabis homologues of the genes that contribute to pyrethrins production in T. cinerariifolium. This provides a plausible pathway for the biosynthesis of pyrethrins in cannabis. Although preliminary, these data indicate a potentially significant confounding variable in both cannabis research and regulations on allowable pyrethrins residues in cannabis products.