Trends in chronic opioid use and association with five-year survival in South Korea: a population-based cohort study

Background: The Korean National Health Insurance Service (NHIS) was developed to provide population data for medical research. The aim of this study was to estimate trends in prescription opioid use in South Korea, and to determine the association between chronic opioid use and 5-yr mortality in cancer and non-cancer patients. Methods: A population-based cohort study was conducted amongst the South Korean adult population using data from the NHIS. Those prescribed a continuous supply of opioids for >= 90 days were defined as chronic opioid users. Multi-variable Cox regression analysis was used to assess the association between chronic opioid use and 5-yr mortality. Results: The proportion of chronic weak opioid users increased from 1.03% in 2002 to 9.62% in 2015. The proportion of chronic strong opioid users increased from 0.04% in 2002 to 0.24% in 2015. In the 2010 cohort (n=822 214), compared with non-users, chronic weak opioid users had a significantly lower 5-yr mortality (hazard ratio [HR]: 0.93; 95% confidence interval [CI]: 0.89-0.96; P<0.001), and chronic strong opioid users had a significantly higher 5-yr mortality (HR: 1.45; 95% CI: 1.28-1.63; P<0.001). Similar results were observed in non-cancer patients, but chronic weak opioid users were not significantly associated with 5-yr mortality in cancer patients (P=0.063). Conclusions: In South Korea, chronic opioid use has increased since 2002. Chronic strong opioid use was associated with a higher 5-yr mortality, and chronic weak opioid use was associated with a slightly lower 5-yr mortality. However, the findings regarding chronic weak opioid users should be interpreted carefully because there might be residual con-founders in this study. Further study is needed to confirm these retrospective findings.