Introduction Management of prescription medicines is challenging for older patients due to frail health and the prevalence of multiple chronic conditions. A salient policy challenge of prescribing practices is that all physicians are not well informed about the national clinical guidelines. A feasible policy intervention to mitigate the harms caused by Potentially Inappropriate Medications is to influence the frequency of prescribing and other prescribing attributes of the drugs by providing accurate and up-to-date information about the national clinical guidelines.

Objectives The objective of this study was to examine the effect of a nationwide information intervention on physicians’ prescribing practices and patients’ healthcare utilization.

Methods We used a quasi-experimental research design based on difference-in-differences variation and nationwide register data on prescribers and purchasers of pregabalin, nortriptyline, and amitriptyline combinations in Finland between January 2018 and May 2019. The study included 68,914 patients and 11,432 physicians.

Results We found that the information letter sent to all prescribers of pregabalin, nortriptyline, or amitriptyline combinations to patients aged 75 years or older decreased the probability of prescribing of these medications. The estimated effect of − 3.3 percentage points (95% confidence interval [− 0.041, − 0.024]) corresponds to a 29% reduction compared to the baseline mean of the outcome. The filled quantity, measured in Defined Daily Doses, of pregabalin, nortriptyline, and amitriptyline combinations per month was reduced by 11.7% [− 14.5% to − 8.9%] among patients aged 75 years or older. No effect on patients’ healthcare utilization was observed.

Conclusions Findings of the study suggest that personal information intervention was an effective policy tool for nudging physicians to reduce prescribing of potentially inappropriate medicines, whereas the reduction in prescribing was not accompanied by improvements or adverse effects in patients’ health.