Impact of a physician-targeted letter on opioid prescribing.

We study the effect of a physician-targeted nudge letter on opioid prescribing. In May 2017, the Social Insurance Institution of Finland sent a personal information letter to all physicians who had issued a prescription containing at least 100 tablets of paracetamol-codeine combination to a new patient. The aim of the letter was to draw the physicians' attention to their prescribing practices and to decrease the size of the first codeine prescription. Using individual level register data and a difference-in-differences strategy, we estimate that the letter decreased the average number of tablets purchased by new patients by 12.5 percent and the probability of a first purchase being at least 100 tablets by six percentage points. We also find that these effects were larger among consistent high prescribers. However, we do not find similar effects on other mild or strong opioids.