Emerging data points to a potential heroin use epidemic in South Africa. Despite this, access to methadone maintenance therapy and other evidence-based treatment options remains negligible. We aimed to assess retention, changes in substance use and quality of life after 6 months on methadone maintenance therapy provided through a low-threshold service in Durban, South Africa.We enrolled a cohort of 54 people with an opioid use disorder into the study. We reviewed and described baseline socio-demographic characteristics. Baseline and 6-month substance use was assessed using the World Health Organization's Alcohol Smoking and Substance Use Involvement Screening Test (ASSIST) and quality of life, using the SF-12. We compared changes at 6 months on methadone to baseline using the Wilcoxon signed rank test and paired-tests for the ASSIST and SF-12 scores, respectively. McNemar's test was used for comparisons between paired results of categorical variables relating to injecting frequency.The majority of the participants were young, Black African males, with a history of drug use spanning over 10 years. Retention after 6 months was 81%. After 6 months, the median heroin ASSIST score decreased from 37 to 9 (p < 0.0001) and the cannabis ASSIST score increased from 12.5 to 21 (p = 0.0003). The median mental health composite score of the SF-12 increased from 41.4 to 48.7 (p = 0.0254).Interim findings suggest high retention, significant reductions in heroin use and improvements in mental health among participants retained on methadone maintenance therapy for 6 months. Further research into longer term outcomes and the reasons contributing to these changes would strengthen recommendations for the scale-up of methadone maintenance therapy in South Africa.