There is a significant correlation between these two distributions (Spearman rank correlation = 0.89), as well as some clear discrepancies: "Kinase" is, by far, the most populated class in drugs, followed by "7TM1", but in metabolites the first class is the later, while "Kinase" is the third one; another large difference is "Hydrolases", the 4 th most populated target class in drugs but the 9 th in metabolites; and "Epigenetic regulator", the 4 h class in metabolites (together with "Oxidoreductase"), but the 10 th in drugs. From the counts of shared vs not shared targets between the two compound sets (Table in Supporting Information) it is possible to see that the target class having the largest counts of targets only interacted with metabolites is "Other" (24), followed by "Transferase" (23), "7TM1" (18) and "Epigenetic regulator" (17).