Opioids are commonly used for pain management in residential aged care homes (RACHs), yet older adults face heightened risks of opioid-related harms. Despite national initiatives to reduce opioid overuse in Australia, trends in RACHs remain poorly described. This study characterised opioid use trends, identified predictors, and examined RACH -level variations. A retrospective longitudinal cohort study was conducted using electronic medication administration records from 428 Australian RACHs during 2018 to 2022. Multivariable Poisson regression identified predictors of monthly opioid use. Home-level variation was assessed using a funnel plot of risk-adjusted indirectly standardised rates. A total of 52,207 residents from 428 homes were included. Annual opioid use declined from 46.8% in 2018 to 44.1% in 2022, with a more pronounced decline in metropolitan homes (46.6% to 41.9%) compared with regional homes where use increased (48.0% to 49.6%). Chronic opioid use (≥90 consecutive/≥120 non-consecutive days) fell markedly from 67.9% in 2018 to 52.4% in 2022 among opioid users. Female sex (RR 1.31) and diabetes (RR 1.04) were associated with higher opioid use, while dementia (RR 0.76) and metropolitan location (RR 0.85) were associated with lower use after adjusting for other factors. After risk adjustment, 29.4% of homes fell outside the 95% control limits with 12.6% exceeding the 99.8% limits in both directions -at which deviation is considered unlikely attributable to chance. These findings highlight persistent and heterogeneous opioid use across Australian RACHs. The substantial variation in risk adjusted opioid use rate suggests targeted quality improvement is needed to support safe and equitable opioid prescribing.