State prescription drug monitoring programs (PDMPs) aim to reduce risky controlled-substance prescribing, but early programs had limited impact. Several states implemented robust features in 2012-13, such as mandates that prescribers register with the program and regularly check its registry database. Some states allow prescribers to fulfill the latter requirement by designating delegates to check the registry. The effects of robust PDMP features have not been fully assessed. We used commercial claims data to examine the effects of implementing robust PDMPs in four states on overall and high-risk opioid prescribing, comparing those results to trends in similar states without robust PDMPs. By the end of 2014 the absolute mean morphine-equivalent dosages that providers dispensed declined in a range of 6-77 mg per person per quarter in the four states, relative to comparison states. Only in one of the four states, Kentucky, did the percentage of people who filled opioid prescriptions decline versus its comparator state, with an absolute reduction of 1.6 percent by the end of 2014. Robust PDMPs may be able to significantly reduce opioid dosages dispensed, percentages of patients receiving opioids, and high-risk prescribing.