Our study presents important evidence of the positive impact of retention in OST on HIV outcomes. Increasing access to OST based on a comprehensive model of care for HIV-infected patients who have indications for OST may foster adherence and ensure long-term response to HAART.

Both access to and effectiveness of OST contribute to sustaining adherence to HAART in HIV-infected IDUs. These results advocate strongly the need of wider use of OST in countries scaling-up HAART where HIV is driven by IDUs.