Purpose Codeine, an analgesic drug acting on μ-opiate receptors, undergoes o-demethylation by CYP2D6 to the active metabolite morphine (about 10% of parent drug), and morphine is further glucuronidated to M3G and M6G.Morphine and its glucuronidated metabolites strongly contribute to the analgesic, antitussive and antidiarrheal effects commonly associated with codeine.Therefore, the influence of the CYP2D6 genetypes on codeine pharmacokinetics has been examined in Chinese population.Methods 29 adult Chinese volunteers in good health participated in this study.Ablood sample was obtained.for genotyping and serial blood samples were drawn to measure codeine and its metabolites in the plasma before and after a single oral dose of 30 mg codeine.Codeine and its metabolites were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.CYP2D6 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RELP) method.Subjects were categorized into the following 3 groups: Group I (n =10): CYP2D6* 1/* 1; Group 2 (n =10): CYP2D6*1/*10 and Group 3 (n =9):CYP2D6*10/*10.All statistics were performed using SPSS 17.0, and a P value of 0.05 or less was regarded as significant.Results Significant differences among the three groups were detected in AUC and Cmax o.f morphine, M3G and M6G (P < 0.05).The Cmax of morphine, M3G and M6G were 78%, 94% and 55% higher in Group 1 subjects than in Group 2 subjects and 86% 139% and 113%higher than in Group 3 subjects, respectively The AUC of morphine, M3G and M6G were 39%, 54% and 55% higher in Group 1 subjects than in Group 2 subjects and 59%, 84% and 115% than in Group 3 subjects, respectively.Conclusion These results suggest that CYP2D6*10 influences the pharmacokinetics of codeine in a Chinese population.