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Caffeine metabolites that were analyzed in the subject urine samples, including caffeine and two of its secondary metabolites—paraxanthine and theophylline (∑caffeine)—and the non-caffeine metab-olites, trigonelline, p-coumaric acid and caffeic acid (∑ncm). Also shown are the cytochrome P450 mixed-function oxidases (CYP1A2 and CYP2E1) that convert caffeine to these secondary metabo-lites.
