OBJECTIVES: The objective of this study was to analyze and describe the drug cost development of the two most commonly prescribed antidepressant drugs in Finland following the introduction of generic substitution by pharmacists in April 2003. METHODS: The prescription claims database of the Social Insurance Institution of Finland was used to calculate the quarterly cost of reimbursements per user for citalopram and fluoxetine from January 2003 to June 2004. Price data were extracted from the registry of the Association of Finnish Pharmacies for April 2003 to April 2004. RESULTS: The quarterly cost of citalopram and fluoxetine per user to the Social Insurance Institution of Finland decreased by 45 % and 48 % respectively one year following the introduction of generic substitution. The companies which marketed the brand name drugs in Finland adopted two contrasting pricing policies in response to generic substitution. A “pseudo-generic” version of citalopram, but not fluoxetine, was available throughout the study period. Regardless of the pricing policy, cost savings of the same level were realized for both patients and government. These cost reductions did not lead to a corresponding increase in the use of citalopram or fluoxetine. CONCLUSION: The introduction of generic substitution was followed by a decrease in price for the two most commonly prescribed antidepressant drugs in Finland. High price elasticity was observed within but not between active ingredients. Price did not appear to guide antidepressant prescribing by physicians.