Background: The objective of this study was to determine the effectiveness of MMT program among injecting drug users (IDUs) in Kota Bharu , Kelantan. Methods: The study was a retrospective study based on the records of injecting drug users (IDUs) involved in the MMT program from November 2005 to 31st January 2008, registered at the Psychiatric Clinic of Hospital Raja Perempuan Zainab II. Opiate Treatment Index (OTI) was used as the research instrument. Repeated measures ANCOVA was used to compare the mean scores during the entry period and after completing twelve months of MMT program after adjusted for age, marital status and level of education. Results: A total of 117 file records were reviewed. There was significant reduction in the mean scores after 12 months of heroin Q score , HIV Risk-taking Behavior Scale and health scale after adjusted for age, marital status and level of education. For Heroin Q score, mean difference was 2.01 (95% CI: 1.45, 2.56), for HIV Risk-taking Behavior Scale, mean difference was 7.64 (95% CI: 6.03, 9.26); and for health scale, mean difference was 5.35(95% CI: 3.90, 6.79). Conclusion: This study supports the evidence that MMT program is effective in treating heroin and opiate dependence.