Initial opioid prescription patterns and the risk of ongoing use and adverse outcomes.

PURPOSE: As clinical practice moves towards more judicious opioid prescribing, physicians require information on how to safely initiate opioids. The objective of this study was to examine the association between initial opioid prescription characteristics and risks of harm and long-term use. METHODS: We conducted a population-based retrospective cohort study among Ontario residents newly dispensed an opioid for pain between July 2013 and March 2016. The primary exposure was the average daily opioid dose dispensed at initiation (in milligram morphine equivalents; MME), with secondary exposures including the initial prescription's duration and formulation. The primary outcome was fatal or non-fatal opioid overdose. A secondary analysis studied continued opioid use for at least 1 year. RESULTS: Among the 2 021 371 individuals meeting our inclusion criteria, 1121 (0.56 per 1000 person-years) experienced an opioid overdose within 1 year and 64 013 (3.17%) continued treatment for at least 1 year. Higher initial daily dose, longer prescription duration, and receipt of a long-acting formulation at initiation were significantly associated with higher hazard of overdose. Compared to daily doses of 20 MME or lower, initial doses exceeding 200 MME daily were associated with a particularly high hazard of overdose (aHR 2.97, 95% confidence interval [CI] 1.62 to 5.44). In the secondary analysis, there were similar associations between initial dose, duration, and formulation and long-term use. CONCLUSIONS: Although the absolute risk of an opioid overdose within the first year of prescription opioid use is low, better alignment of opioid initiation practices with guidelines may reduce opioid-related harm.