Factors Associated with Changes in Opioid Analgesic Prescribing after Opioid Agonist Treatment Initiation: A Nationwide Registry Cohort Study

Background:Pain is common among individuals receiving opioid agonist treatment (OAT). This study aims to investigate factors associated with changes in opioid analgesic dispensing among treatment-naïve patients initiating OAT. Methods:We analyzed nationwide health and dispensing records of patients initiating OAT (N = 3783) in Norway from 2014 to 2023. The cohort included new OAT patients who completed their first year of treatment. The primary outcomes were changes in opioid analgesic use during the year before and after OAT initiation. Logistic regression was used to identify factors associated with continued opioid analgesic use after initiating OAT. Results:Over one-third (n = 1329, 35%) of new OAT patients were prescribed opioid analgesics in the year prior to treatment initiation. Following OAT, there was a 37% reduction. Daily opioid amounts in morphine milligram equivalents decreased after OAT initiation across all four percentile strata. Continued opioid analgesic use after initiation of OAT was more likely among women (adjusted odds ratio [aOR] 1.32, 95% CI 1.04-1.68) and participants aged > 56 years (aOR 1.71, CI 1.07-2.72). Pain-related diagnoses (aOR 2.45, CI 1.93-3.11), depression or anxiety disorders (aOR 1.59, CI 1.23-2.03), and bipolar/schizophrenia disorders (aOR 1.89, CI 1.19-2.98) were associated with higher odds of continued opioid analgesic use. Conclusions:Opioid analgesic use was prevalent among OAT patients before treatment initiation, with reductions observed within one year. Continued opioid use among those with pain suggests that OAT alone may not fully address pain management needs.