<h3>Background & Aims</h3> People who inject drugs (PWID) and are on opioid agonist therapy (OAT) might have lower adherence to direct-acting antivirals (DAAs) against hepatitis C virus (HCV) and, therefore, lower rates of sustained virologic response (SVR). Because of this, we compared the SVR rates to interferon-free DAA combinations in individuals receiving OAT and those not receiving OAT in a real-world setting. <h3>Methods</h3> The HEPAVIR-DAA cohort, recruiting HIV/HCV-coinfected patients (NCT02057003), and the GEHEP-MONO cohort (NCT02333292), including HCV-monoinfected individuals, are ongoing prospective multicenter cohorts of patients receiving DAAs in clinical practice. We compared SVR 12 weeks after treatment (SVR12) in non-drug users and PWID, including those receiving or not receiving OAT. Intention-to-treat and per protocol analyses were performed. <h3>Results</h3> Overall, 1,752 patients started interferon-free DAA treatment. By intention-to-treat analysis, 778 (95%, 95% CI 93%–96%) never injectors, 673 (92%, 95% CI 89%–93%) PWID not on OAT and 177 (89%, 95% CI 83%–92%) PWID on OAT achieved SVR12 (<i>p</i> = 0.002). SVR12 rates for ongoing drug users (with or without OAT) were 68 (79%) compared with 1,548 (95%) for non-drug users (<i>p</i> <0.001). Among ongoing drug users, 15 (17%) were lost-to-follow-up, and 3 (3.5%) became reinfected. In the per protocol analysis, 97% never injectors, 95% PWID not on OAT and 95% PWID on OAT achieved SVR12 (<i>p</i> = 0.246). After adjustment, ongoing drug use was associated with SVR12 (intention-to-treat) and OAT use was not. <h3>Conclusions</h3> HCV-infected PWID achieve high SVR12 rates with DAAs whether they are on OAT or not, but their response rates are lower than those of patients who never used drugs. This is mainly attributable to more frequent loss to follow-up. Accounting for active drug use during DAA therapy nearly closed the gap in SVR rates between the study groups. <h3>Lay summary</h3> Patients with hepatitis C virus infection who are on opioid agonist therapy can achieve high cure rates with current treatments. The use of illicit drugs during treatment can drive drop-outs and reduce cure rates. However, hepatitis C can be cured in most of those using drugs who complete treatment and follow-up. Clinical trial number: HEPAVIR-DAA cohort, NCT02057003; GEHEP-MONO cohort, NCT02333292.

Response to direct-acting antiviral therapy among ongoing drug users and people receiving opioid substitution therapy