OBJECTIVE: There is little research describing the effects of the introduction of generic fluoxetine to the SSRI market. The purpose of this analysis is to examine utilization of the SSRI class in a Pennsylvania Medicaid HMO before and after the launch of fluoxetine (generic) into the US marketplace. METHODS: Generic fluoxetine became available in August 2001. Pharmacy claims data from January 2000 to December 2002 were used to analyze utilization of the SSRI class (consisting of the following: Celexa, Zoloft, Paxil, Effexor XR, Prozac, and fluoxetine). Utilization data for each drug in the class were separated into two group periods, pre- and post introduction of generic fluoxetine. The pre- and post periods consisted of 19 and 17 months respectively. Utilization of Prozac and fluoxetine was used as a reference to compare utilization of other drugs in the class. T-test analysis was used to compare and show differences between pre- and post- periods for each drug. RESULTS: Prozac /fluoxetine average monthly prescription utilization for pre- and post- periods were 3434.16 and 4349.56 respectively (p <0.001), which indicates an average increase in monthly utilization by 27%. Celexa average monthly utilization for pre- and post- periods were 1252.95 and 2848.4 respectively (p <0.001), demonstrating an increase in utilization by 127%. Effexor XR average monthly utilization during pre- and post- periods were 908.58 and 2084.38 respectively (p <0.001), indicating an increase of 129%. Paxil average monthly utilization for pre- and post periods were 2834.9 and 4059.6 respectively (p <0.001), indicating an increase of 43%. Lastly, Zoloft's average monthly utilization for pre- and post periods were 3915.05 and 4615.88 respectively (p <0.001), which resulted in an increase of 18%. CONCLUSION: In this managed care setting a significant increase in monthly utilization was seen for all drugs with the exception of Zoloft.