The opioid crisis remains a significant public health concern, with fentanyl contributing
to 79% of accidental opioid-related deaths in Canada between January and June 2024, nearly a
40% increase since the national surveillance in 2016. Opioid agonist therapy (OAT), using
medications such as methadone and buprenorphine, is an evidence-based treatment for opioid
use disorder (OUD) that aims to reduce harm and mortality. While OAT is increasingly delivered
in primary care to improve accessibility, patient retention in these programs remains a significant
challenge. Retention is a commonly used outcome in OUD treatment studies; however, there is
no universal definition. This integrative review explores the factors influencing OAT retention
among individuals with opioid use disorder in primary care settings. A systematic search of peerreviewed literature published from 2016 to 2024 identified nine U.S.-based studies, including
three qualitative and six cohort studies. Findings indicate that comorbid mental health and
substance use disorders, along with limited access to psychosocial supports, negatively affect
retention. Conversely, low-barrier, trauma-informed, and multidisciplinary care models are
associated with improved outcomes. These findings highlight the need for OAT programs to
adapt to the complex needs of patients with OUD by providing individualized, flexible, and
accessible treatment options. Integrating mental health and addiction care within primary care
settings may improve patient engagement and decrease opioid-related harm and mortality.
