“Of central importance was the novel finding that THC can be detected in serum and brain after administration of CBD alone which, if confirmed in humans and given the increasing medical use of CBD-only products, might have important legal and forensic ramifications.” https://www.ncbi.nlm.nih.gov/pubmed/29129557  http://www.europeanneuropsychopharmacology.com/article/S0924-977X(17)30983-5/fulltext