A total of 120 newly-enrolled treatment-seeking OUD patients will be randomly assigned to one of two different groups: either methadone plus daily open-label placebo (OLP; treatment group), or methadone/Treatment as Usual (TAU; control). Participants will meet with study team members five times over the course of three months of treatment with methadone (baseline, 2 weeks, and 1, 2 and 3 months post-baseline). Throughout this study time period, methadone dosages will be adjusted by an addiction clinician blind to patient assignment, per standard clinical methods. The primary outcome is methadone dose at three months. Secondary outcomes include self-report of drug use; 3-month urine toxicology screen results; and treatment retention. Exploratory outcomes include several environmental as well as personality factors associated with OUD and with propensity to demonstrate a placebo effect.