Please use this link to access this publication. Abstract No analytical assay is currently available for the simultaneous determination of CBD major metabolites in serum or urine samples of individuals treated with medical cannabis or CBD-based pharmaceuticals. We developed and validated a method using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC–MS/MS) for quantifying cannabidiol (CBD) and its metabolites, cannabidiol-7-oic acid (7-COOH-CBD), 7- hydroxycannabidiol (7-OH-CBD), 6-alpha-hydroxycannabidiol (6-α–OH–CBD) and 6-beta-hydroxycannabidiol (6-β–OH–CBD) in serum and urine samples of an individual treated with medical cannabis. The ionization was performed by electrospray in negative mode to reach the sensitivity required to detect trace amounts, with limits of quantification ranging from 0.05 to 0.1 ng/mL. The...