Continuity of Primary Care and Delayed Opioid Initiation in Non‐Cancer Pain: A Cohort Study

BACKGROUND: Continuity of care is a core element of high-quality primary care and may prevent inappropriate opioid use. However, evidence on its association with opioid initiation among opioid-naïve adults with non-cancer pain remains scarce. METHODS: We conducted a population-based cohort study using South Korea's national claims data (2015-2022). The study included 392,988 adults aged ≥ 20 years diagnosed in 2016 with musculoskeletal and connective tissue disorders who received outpatient primary care without prior opioid exposure. Continuity of care was measured using the Bice-Boxerman Continuity of Care Index (COCI) and categorised as high (≥ 0.90), medium (0.48-< 0.90), or low (< 0.48). The primary outcomes were the incidence of new opioid prescriptions and a composite indicator of potentially inappropriate opioid prescribing, defined by five criteria. RESULTS: Among 392,988 participants, 52,670 (13.4%) initiated opioid therapy. Compared with the high-continuity group, the medium- and low-continuity groups had 1.27-fold (95% CI, 1.25-1.28) and 1.43-fold (95% CI, 1.41-1.45) higher risks of opioid initiation, respectively. High continuity was associated with a median delay of 303 days in opioid initiation. Potentially inappropriate prescribing occurred in 12.1% of opioid users, with higher risks in the medium- (adjusted hazard ratio [aHR] = 1.26; 95% CI, 1.23-1.28) and low-continuity groups (aHR = 1.41; 95% CI, 1.39-1.44). CONCLUSIONS: Higher continuity of primary care was associated with delayed opioid initiation and reduced inappropriate opioid prescribing among adults with non-cancer pain. Strengthening continuity-focused interventions may help mitigate opioid-related harms and promote safer pain management. SIGNIFICANCE STATEMENT: Relational continuity in primary care plays a key role in shaping opioid prescribing patterns among adults with non-cancer pain. Using nationwide data, our findings suggest that stronger continuity is associated with more cautious opioid use, including delayed initiation and a lower likelihood of inappropriate prescribing. These results highlight the importance of fostering ongoing, trust-based relationships between patients and primary care providers as a strategy to reduce unnecessary opioid exposure and promote safer, patient-centered pain management. Strengthening continuity in primary care may therefore have meaningful implications for both clinical practice and health policy.