Ho ISS, et al. - Given a significant and negative impact of poor adherence to antiretroviral regimens on individual and global health among HIV-positive drug users, researchers sought to recognize knowledge gaps and inconsistencies within the current evidence base and to estimate HIV-positive drug users’ adherence rates and the factors that determine their adherence. They searched Applied Social Sciences Index and Abstract, Cumulative Index to Nursing and Allied Health Literature, Medline, Embase and PsycINFO (Ovid interface) for studies related to HIV-positive drug users’ adherence to antiretroviral treatment. They identified a wide variation in the proportion of HIV-positive drug users who achieved ≥ 95% adherence across the studies, from 19.3 to 83.9%. The following factors were identified influencing adherence: stigmatization, motivation, active drug use, accessibility and conditionality of HIV and addiction care, side effects and complexity of treatment regimens, forgetfulness and non-incorporation of dosing times into daily schedules. These findings suggest that HIV-positive drug users’ medication-taking is a dynamic social process and health professionals need to regularly assess adherence to HIV treatment.