Change in prescription opioid dose and the risk of mental health-related and substance use-related emergency department presentations: a case-crossover study.

Opioid deprescribing is recommended to reduce opioid-related harms; however, research suggests that opioid dose changes may lead to adverse health outcomes. We aimed to determine if opioid dose changes are associated with mental health-related or substance use-related emergency department (ED) presentations. This self-controlled case-crossover study used POpulation Level Analysis and Reporting (POLAR) primary care data linked with data from 3 metropolitan hospitals in Victoria, Australia. People who had a mental health-related or substance use-related ED (MHSU-ED) presentation between April 2018 and May 2022 and had received ≥4 opioid prescriptions in the 12 months preceding their ED presentation were included. Adjusted odds ratios (aOR) for MHSU-ED presentations were estimated using conditional logistic regression, comparing opioid dose change in the 30 days before MHSU-ED presentation to that in 5 corresponding sets of control periods of equal length not immediately preceding MHSU-ED presentation. Of the 1458 eligible patients, 75.9% experienced a >25% reduction in their prescribed opioid dose in the 30 days before MHSU-ED presentation. Compared with receiving no opioid prescriptions in the 30 days prior, a >25% reduction in prescribed opioid dose (aOR: 1.78; 95% confidence interval [CI]: 1.44-2.21) or opioid discontinuation (aOR: 2.04; 95% CI: 1.48-2.82) was linked to higher odds of a MHSU-ED presentation whilst a 10% to 25% reduction (aOR: 0.15; 95% CI: 0.10-0.23) or a stable or increased dose (aOR: 0.01; 95% CI: 0.008-0.022) was associated with lower odds of MHSU-ED presentation. Larger opioid dose reduction or discontinuation is associated with increased risk of subsequent mental health-related and substance use-related ED presentations.