Drug-drug Interaction Study of Bemnifosbuvir/Ruzasvir (BEM/RZR) and Buprenorphine/Naloxone or Methadone

Inclusion Criteria: * Must agree to use acceptable contraceptive methods through at least 90 days after the last dose of study drug. * Minimum body weight of 50 kg and body mass index (BMI) of 18-32 kg/ m2. * Willing to comply with the study requirements and to provide written informed consent. Exclusion Criteria: * Infected with hepatitis B virus, hepatitis C virus, HIV. * Abuse of alcohol or drugs. * Use of other investigational drugs within 28 days prior to Day -5. * Concomitant use of prescription medications, or systemic over-the-counter medications (apart from methadone or buprenorphine/naloxone as assigned maintenance therapy). * Other clinically significant medical conditions or laboratory abnormalities.