For a study, adequate medication adherence was essential for those who injected drugs to achieve a sustained viral response (SVR) to the hepatitis C virus (HCV) (PWID). However, it was unclear which patterns of direct-acting antiviral (DAA) treatment adherence were linked to SVR in this cohort, or what determinants were involved. Electronic blister packs were used by the randomized three-arm PREVAIL to collect daily time frame adherence data in opiate agonist therapy program settings in a randomized three-arm design. The correlations between SVR and six different types of treatment adherence patterns were investigated using exact logistic regressions. SVR was attained in 109 (96.5%) of the 113 subjects who were given a combination of DAAs. Except for the number of switches between adherent and missed days, SVR was significantly associated with all pattern parameters: total adherent daily doses (exact adjusted odds ratio [AOR]=1.12; 95% CI=1.04–1.22), % total doses (1.09; 1.03–1.16), days on treatment (1.16; 1.05–1.32), maximum consecutive adherent days (1.34; 1.06–2.04), and maximum consecutive nonadherent days (0.85; .74–.95=0.003). In the first two months of treatment, SVR was associated with total adherent doses, but not in the last month. While drunkenness with alcohol was linked to frequent switching, there was no link between drug use and any adherence pattern. Maintaining good total dose adherence throughout the course of HCV treatment is critical to obtaining SVR among PWID. For treating PWID who become intoxicated due to alcohol, additional integrative addiction and medical care may be required.