Patients will be randomized to one of two models of care: patient navigation (PN) vs. modified directly observed treatment (mDOT). Patients enrolled from OAT clinics who are receiving methadone and randomized to mDOT will receive doses of once daily medication at the same time as they receive methadone. Patients enrolled from community health settings and randomized to mDOT may receive observed doses in a range of settings including: at their clinic, at home, a community site (e.g. at a coffee shop or other gathering place), or using a mobile health app on a smartphone. Subjects randomized to PN will receive a standardized PN intervention and additional support through a peer-led support group.