FA and IFA were actually O-methylated CA on one of the phenolic hydroxyl groups, and all metabolites found in FA and IFA samples could be found in CA samples. We only found mono-methylation in CA samples and none of methylated conjugates after dosing FA or IFA, so methylation did not occur in FA and IFA samples. Conjugation with glucuronic acid was the only reaction, and conjugation on the carboxyl group on the side chain (M4 and M9, respectively) was the main metabolic pathway after dosing of FA or IFA. It was interesting to note that 3-(3-hydroxy-4-methyoxyphenyl) crylic acid glucuronide (M9) could also be found FA samples. We speculated that M9 with the structure 3-hydroxy-4-methoxy-phenyl was more stable than M4 with the structure 3-methyoxy-4-hydroxy-phenyl, so M4 could be transformed to M9 through a transition state with a five-membered ring.