Estimating the effects of reforms in advance is an important part of evidence-based and transparent legislative processes. The aim of this study was to describe a microsimulation method created to produce ex ante estimates of pharmaceutical pricing and reimbursement policy reforms. As a case example, the estimates for the 2016 pharmaceutical reimbursement scheme reform, including, e.g., the introduction of a €50 annual deductible, are presented. A static microsimulation model was developed based on the reimbursed purchases of 380,931 individuals drawn at random (10% sample) from the prescription register. The 2016 reform was projected to create savings of €44 million/year for the National Health Insurance (NHI). For patients, the median annual out-of-pocket costs increased from €78 to €96 (by +€18). For 97%, the estimated change was less than €50/year. The majority of patients whose out-of-pocket costs increased had relatively low prior costs. However, >€50/year increases predominantly affected patients entitled to higher reimbursements based on chronic or severe illnesses, among whom older and lower-income individuals were overrepresented. Increases of >€100 were rare (0.003%) and derived from exceptional circumstances. The microsimulation produced prompt but versatile estimates of the effects of legislative reforms by factoring in the entire spectrum of individual situations among affected patients.