Fluoxetine (Prozac) is a potent antidepressant compound inhibiting serotonin reuptake, but also Na+, K+ and Ca2+ channels and reported to both trigger and prevent apoptosis. Recently, fluoxetine was found to increase the voltage sensitivity of the mitochondrial voltage-dependent anion channel (VDAC). VDAC which functions in transporting metabolites across the mitochondria also plays a crucial role in apoptosis. Here, we demonstrate that fluoxetine interacted with VDAC and decreased its conductance. Fluoxetine inhibited the opening of the mitochondrial permeability transition pore, the release of cytochrome c, and protected against staurosporine-induced apoptotic cell death. These findings may explain some of the reported fluoxetine side effects.