Opioid days' supply limits: an interrupted time-series analysis of opioid prescribing before and following a Massachusetts law.

: In 2016, Massachusetts passed the first-in-the-nation law limiting opioid naïve adults and all minors to a 7-day supply of opioids when prescribed in the outpatient setting.: We hypothesized this policy would be associated with declines in the percent of opioid prescriptions with more than a 7-day supply among opioid naïve adults and minors for select prescriber groups.: Interrupted time series analyses were conducted using measures from the Massachusetts Prescription Monitoring Program database for 2015 through 2017 (n = 13,672,325 opioid prescriptions; 54% to females). Outcomes were the monthly percent of opioid prescriptions greater than 7 days' supply in opioid naïve adults and in minors among select prescriber groups. Model estimates of the pre-policy trend, the average changes in the level pre/post-implementation, and the trend changes post-implementation were assessed.: Pre-policy trends showed significant monthly declines in the percent of opioid prescriptions greater than 7 days' supply for all prescriber groups. Policy implementation was associated with significant reduction in the level for opioid naïve adults among surgeons (-2.92%,  .01), dentists (-0.23%,  .01), and general medical providers (-2.22%, = .04), and for minors among all-included prescribers (-2.97%,  .01) and surgeons (-3.8%,  .01). Post-implementation changes in trends were not significant except among opioid naïve adults for dentists (0.02%, = .04).: Within a context of significant reductions occurring in opioid prescriptions greater than 7 days' supply during this period, the Massachusetts policy was associated with further declines for opioid naïve adults and minors among select prescriber groups.