Pharmacogenetic information in the package insert was reviewed. Most of the information was gene polymorphisms for the drug metabolizing enzymes such as cytochrome-P450 (CYP) and UDP-glucuronyl transferase(UGT), which alter the pharmacokinetics for substrate drugs resulting in individual variation of drug response including efficacy and adverse effects. In the typical substrates for these enzymes (proton pump inhibitors, clopidogrel, irinotecan and warfarin), difference in the pharmacological efficacy and side effects are discussed among the patients groups carrying different genotypes. HLA types identified for drug-induced serious dermatitis and hypersensitivity for abacavir, carbanazepine and alloprinol are also included in this review.