Depression, antiretroviral therapy initiation, and HIV viral suppression among people who inject drugs in Vietnam

•There is a high burden of depression and HIV among people who inject drugs.•Severe depressive symptoms led to decreased initiation of antiretroviral therapy.•There were no differences in viral suppression by depressive symptoms.•Discrepancies in outcomes may be due to reporting bias and missing data. The burden of depression is high among people who inject drugs (PWID) and may contribute to the spread of HIV through poor treatment engagement and persistent viremia. We estimated the effects of depression on antiretroviral therapy (ART) initiation and viral suppression among PWID living with HIV. Longitudinal data were collected from 455 PWID living with HIV in Vietnam during 2009–2013. We estimated the 6- and 12-month cumulative incidence of ART initiation and viral suppression, accounting for time-varying confounding, competing events, and missing data. The cumulative incidence difference (CID) contrasted the incidence of each outcome had participants always vs. never experienced severe depressive symptoms across study visits to date. Severe depressive symptoms decreased the cumulative incidence of ART initiation, with CID values comparing always vs. never having severe depressive symptoms of -7.5 percentage points (95% CI: -17.2, 2.2) at 6 months and -7.1 (95% CI: -17.9, 3.7) at 12 months. There was no appreciable difference in the cumulative incidence of viral suppression at 6 months (CID = 0.3, 95% CI: -11.3, 11.9) or 12 months (CID = 2.0, 95% CI: -21.8, 25.8). Discrepancies between the ART initiation and viral suppression outcomes could be due to under-reporting of ART use and missing data on viral load. Future work probing the seemingly antagonistic effect of depression on treatment uptake – but not viral suppression – will inform the design of interventions promoting HIV clinical outcomes and reducing onward transmission among PWID.