CTN 0064 has two main components: Component 1 is the baseline assessment for CTN 0064. It will also serve as a long-term follow-up assessment for CTN 0049 for those who consent to participate in CTN 0064. Participants whose HCV antibody test result is positive in this baseline assessment will be invited to enroll in Component 2. Component 2 is an RCT that will assess the effectiveness of a Care Facilitation intervention (compared to Control) in moving HIV/HCV co-infected substance users forward along the HCV care continuum. The study's primary objective is based on Component 2 and will be operationalized as movement through a series of (potentially non-sequential) pre-defined, clinical steps along the HCV care continuum (including the ultimate step, sustained virologic response to treatment at 12 weeks post treatment completion [SVR12]) (AASLD/IDSA/IAS-USA). Secondary objectives will be to assess: 1) success at each step in the HCV care continuum, 2) engagement in HIV care and substance use treatment, and 3) HIV viral suppression as well as 4) to examine other long-term outcomes of the CTN 0049 cohort.

This is a 19-week, multi-center, parallel group study that includes: 1) up to 3 weeks for screening; 2) a 13-week Treatment Phase consisting of a 1-week, single-blind run-in period, when all subjects receive twice daily 15 mg acetazolamide capsules (a medication adherence marker), followed by randomization to either twice daily 10 mg lorcaserin or placebo capsules for the remaining 12 weeks; and 3) a 3-week follow-up period, with scheduled visits during Study Weeks 14 and 16.