Flavonoids are a heterogeneous group of phenolic compounds that are biosynthesize by plants, and people ingest them through fruits and vegetables. The basic flavonoid skeleton consists of two benzene rings connected by a pyran. Further differences are based on the existence and distribution of additional hydroxyl and methyl groups. The interest in the study of flavonoids has increased with the knowledge of their action as antioxidants and cardioprotective, anti-inflammatory or antiviral activity. From a pharmacological point of view, they are interesting due to possible interactions with enzymes that metabolize xenobiotics, which are in the highest percentage memebers of cytochromes P450 superfamily. There are studies that show that biotransformation of certain flavonoids is mediated by CYP enzymes, and flavonoids may have an inhibitory or activating effect. Therefore, it is necessary to thoroughly explore the path of flavonoid metabolism and thus to predict medical errors that may arise if a patient is treated with a drug whose metabolic pathways includes an enzyme that also metabolizes flavonoids that are introduced through food or nutritional supplements. Eleven different flavonoids were tested, which by previous screening demonstrated the metabolism catalyzed by CYP enzymes. LC-MS is a chromatographic method that gives us an insight into the existence of a metabolite because it provides information on the molecular weight and structure of the compound, the identification and quantification of the individual sample components. We confirmed the identity of the metabolites for four flavonoids, and they were generated by cytochrome P450 2D6. This enzyme in the reaction with 7-hydroxyphenol and galangine gives hydroxylated metabolites, in the reaction with acacetin hydroxylation gives a new flavonoid apigenin, and in the reactions of tangerine demethylation it gives four different metabolites, one of which is demethylated in two positions. With regard to the cytochrome P450 2D6 polymorphisms and existence of four phenotypes that differ in the rate of biotransformation of drugs, these results are important because we can predict the potential drug-flavonoid interaction and providing a good therapeutic effect of the drug when combinde with flavonoids.