KEGG pathway analysis indicates that the differential metabolites in the four types are primarily associated with ABC transporters, Pyrimidine metabolism, D‐Amino acid metabolism, Central carbon metabolism in cancer, Alanine, aspartate and glutamate metabolism, Protein digestion and absorption, Alcoholism, Glycine, serine and threonine metabolism, Lysine degradation, and so on (Figure 2I). This evidence concerns the gene ABCG2 and alcohol dependence.