Methadone is a synthetic opiate mu receptor agonist that is widely used in the management of opiate dependence is to prevent opiate users from injecting and sharing needles in order to reduce the spread of blood borne viruses. Therefore in this study we aimed to determine the safe and effective dose of methadone in terms of treatment retention rate and re-injecting behaviour. They were treated according to guidelines provided by Ministry of Health Malaysia.We found that adequate daily doses of methadone were an important determinant in order to achieve successful outcome in patients on MMT.