The utilization of generic drugs in medical practice has been promoted in Japan for the purpose of minimizing drug costs. In order to determine the clinical efficacy of the original preparation of glycyrrhizin, in comparison to its generic drug, a controlled longitudinal study was done of 82 consecutive patients with chronic hepatitis C receiving the original preparation of glycyrrhizin for 6 months. Patients treated with the original preparation of glycyrrhizin for 6 months at two hospitals were separated into two groups for study: Patients who changed from the original preparation of glycyrrhizin to a generic drug and then changed back from the generic drug to the original preparation of glycyrrhizin (Group A, n=46) ; and, patients who were continuously treated with the original preparation of glycyrrhizin (Group B, n=36) . HCV RNA levels were serially determined by Cobas Amplicor HCV Monitor assay. In Group A, the ALT level significantly elevated 3 months after switching treatment from the original preparation of glycyrrhizin to the generic drug (from 65.1 ±22.7 IU/L to 1 12.4±39.9 IU/L) (P<0.05), then significantly decreased 3 months after the change back to the original preparation of glycyrrhizin (from 112.4±39.9 IU/L to 62.1±23.0 IU/L) (P<0.05) . In Group B, however, the ALT level did not significantly change during the same observation period. The serum HCV RNA level did not significantly change in either group, even in Group A patients whose ALT levels significantly changed. The efficacy on ALT of the original preparation of glycyrrhizin and the generic drugs differed in patients with chronic hepatitis C.