HIV-infected persons who use drugs (PWUDs) are particularly vulnerable for suboptimal combination antiretroviral therapy (cART) adherence. A systematic review of interventions to improve cART adherence and virologic outcomes among HIV-infected PWUDs was conducted. Among the 45 eligible studies, randomized controlled trials suggested directly administered antiretroviral therapy, medication-assisted therapy (MAT), contingency management, and multi-component, nurse-delivered interventions provided significant improved short-term adherence and virologic outcomes, but these effects were not sustained after intervention cessation. Cohort and prospective studies suggested short-term increased cART adherence with MAT. More conclusive data regarding the efficacy on cART adherence and HIV treatment outcomes using cognitive behavioral therapy, motivational interviewing, peer-driven interventions and the integration of MAT into HIV clinical care are warranted. Of great concern was the virtual lack of interventions with sustained post-intervention adherence and virologic benefits. Future research directions, including the development of interventions that promote long-term improvements in adherence and virologic outcomes, are discussed.