PURPOSE: In June 2013 a European Medicines Agency referral procedure concluded that diclofenac was associated with an elevated risk of acute cardiovascular events and contraindications, warnings, and changes to the product information were implemened across the European Union. This study measured the impact of the regulatory action on the prescribing of systemic diclofenac in Denmark, The Netherlands, England, and Scotland. METHODS: Quarterly time series analyses measuring diclofenac prescriptioninitiation, discontinuation and switching to other systemic nonsteroidal anti-inflammatory (NSAIDs), topical NSAIDs, paracetamol, opioids, and other chronic pain medication in those who discontinued diclofenac. Absolute effects were estimated using interrupted time series regression. RESULTS: Overall, diclofenac prescription initiations fell during the observation periods of all countries. Compared with Denmark where there appeared to be amore limited effect, the regulatory action was associated with significant immediate reductions in diclofenac initiation in The Netherlands (-0.42%, 95% CI, -0.66% to -0.18%), England (-0.09%, 95% CI, -0.11% to -0.08%), and Scotland (-0.67%, 95% CI, -0.79% to -0.55%); and falling trends in diclofenac initiation in theNetherlands (-0.03%, 95% CI, -0.06% to -0.01% per quarter) and Scotland (-0.04%, 95% CI, -0.05% to -0.02% per quarter). There was no significant impact on diclofenac discontinuation in any country. The regulatory action was associated with modest differences in switching to other pain medicines following diclofenac discontinuation. CONCLUSIONS: The regulatory action was associated with significant reductions in overall diclofenac initiation which varied by country and type of exposure. There was no impact on discontinuation and variable impact on switching.