The objective of the present study was to evaluate changes in platelet counts on three different kinds of antidepressant. All subjects (n = 131) in their drug-naïve state had been diagnosed with depression. Escitalopram (n = 42), venlafaxine (n = 50) and bupropion (n = 39) were prescribed, and platelet count was measured before and after 1 month of treatment and compared. Decrease in platelet count on escitalopram was significant, while the others were not. These findings suggest that escitalopram may be associated with decreased platelet count, and bupropion is less likely to exert an influence on platelet count.