LC-MS/MS analysis and post-column infusion. Chromatographic separation and MS/MS analysis was performed according to the low pH method described by Di Zazzo et al. , using the same ternary mobile phase system and column (Acquity BEH C18 column (50 mm x 2.1 mm, 1.7 µM) (Waters, Milford, MA, USA)), but transferred to a Shimadzu Nexara X2 UHPLC system (Shimadzu, Kyoto, Japan) coupled to a Sciex QTRAP 6500+ MS (Sciex, Framingham, MA, USA) with electrospray ionization. The injection volume was 10 µL and mobile phase A was used as a stacking solution to avoid breakthrough. While the method was developed and validated to analyze a variety of metabolic classes, including oxylipins, oxidative stress markers and bile acids, this study only investigated endocannabinoids. The LC and MS method details can be found in the SI (Table ). Because of uncontrolled isomerization between 1-AG and 2-AG, isomer peaks of 1-AG and 2-AG were integrated as a double peak (and referred to as 1/2-AG). Also d8-2AG was integrated as a double peak.