Background: Prescription drug monitoring programs (PDMPs) are central to the federal and state policy responses to address prescription drug abuse. PDMPs are state-run electronic databases used to track the prescribing and dispensing of controlled prescription medications. Despite their prominence, there is limited and mixed evidence of PDMP effectiveness, particularly among vulnerable populations. This study aimed to evaluate the influence of PDMP implementation and program rigor on prescription opioid utilization among disabled and older adults. Methods: A retrospective study using 2007-2012 Medicare claims and PDMP state laws from the Prescription Drug Abuse Policy System was designed to quantify associations between PDMP status or rigor and state- and individual-level opioid utilization (opioid volume, days supplied, daily morphine equivalents, number of prescriptions, daily dose ≥120mg), accounting for sociodemographic characteristics and state controlled substance laws. A PDMP composite score was developed from the total number of best practices adopted by each state (range: 0-14), classifying states according to the median score ("high PDMP rigor" and "low PDMP rigor"). Generalized linear, negative binomial, and modified Poisson regression models adjusting for clustering were applied. Results: From 2007-2012, the number of states operating PDMPs rose from 27 to 44. PDMP implementation was associated with reduced opioid volume (-2.36kg/month, 95% CI -3.44, -1.28) compared to non-PDMP states. Observed reductions were stronger in disabled adults than older adults. Annual prescription rates per 10,000 opioid-users were lower in states with low PDMP rigor (-578 [95% CI: -1006, -151]) or high rigor (-687 [95% CI: -1081, -293]) than non-PDMP states. At the individual level, PDMPs of any rigor were associated with decreased opioid utilization. There was no significant evidence that estimated associations between states with low and high rigor PDMPs were different. Conclusions: Findings suggest PDMP rigor has limited impact on individual-level opioid utilization among Medicare beneficiaries. Further studies are needed to elucidate which PDMP characteristics add value rather than adding operating cost and effort with little return.