“Cannabidiol (CBD) products have ascribed an uprising trend for their health-promoting effects worldwide. In contrast to Δ9-tetrahydrocannabinol (THC), CBD exhibits no state of euphoria. Since conversion of CBD into THC in an acidic environment has been reported, it has not been proved whether this degradation will also occur in human gastric fluid.
A total of 9 subjects ingested 400 mg CBD as a water-soluble liquid together with lecithin as an emulsifier and ethanol as a solubilizer. Blood samples were taken up to 4 h, and urine samples were submitted up to 48 h. THC, 11-hydroxy-Δ9-THC (THC-OH), 11-nor-9-carboxy-Δ9-THC (THC-COOH), CBD, 7-hydroxy cannabidiol (7-OH-CBD), and 7-carboxy cannabidiol (7-CBD-COOH) were determined in blood and THC-COOH and 7-CBD-COOH in urine by LC-MS/MS. Neither THC, THC-OH, nor THC-COOH were detectable in any serum specimen. Only two urine samples revealed THC-COOH values slightly above the threshold of 10 ng/ml, which could also be caused by trace amounts of THC being present in the CBD liquid.
It can be concluded that negative consequences for participants of a drug testing program due to a conversion of CBD into THC in human gastric fluid appear unlikely, especially considering a single intake of dosages of less than 400 mg.
Nevertheless, there is a reasonable risk for consumers of CBD products being tested positive for THC or THC metabolites. However, this is probably not caused by CBD cyclization into THC in human gastric fluid but is most likely due to THC being present as an impurity of CBD products.”
https://pubmed.ncbi.nlm.nih.gov/36190564/
https://link.springer.com/article/10.1007/s00414-022-02896-w