The need to achieve ≥95 % adherence to HAART for treatment effectiveness may be a barrier for universal initiation at early stages of HIV. Using longitudinal data collected from 2006 to 2011 from cohort studies of MSM (MACS) and IDUs (ALIVE study), we estimated the minimum adherence needed to achieve HIV RNA suppression (<50 copies/mL), defined as the level at which at least 80 % were virally suppressed, and the odds of suppression was not significantly different than that observed with ≥95 % adherence. In the MACS, ≥80 % suppression was observed with 80-84 % adherence and the odds ratio for suppression (vs. ≥95 % adherence) was 1.43 (0.61, 3.33). In the ALIVE study where <35 % were on newer drugs, only 71.4 % were suppressed among those who reported ≥95 % adherence. Although IDUs on older HAART regimens may need to be ≥95 % adherent, concerns related to non-adherence may be less of a barrier to initiation of modern HAART regimens.