The anti-impotence drug.

The anti-impotence drug viagra actually reduces men's fertility by decreasing the ability of their sperm to fertilize an egg, according to a study conducted by researchers at Queen's University Belfast and published in the journal Fertility and Sterility.
Researchers carried out two different experiments to determine what effect the popular drug might have on sperm cells. In the first study, human sperm samples were bathed in weak viagra solutions, intended to approximate the blood concentration acquired from taking a single 100-milligram viagra pill. They found that while the viagra-bathed sperm became more active, they also suffered damage to the structure at their heads known as the acrosome. This portion of the cell contains enzymes that help break down the membrane around an egg so that the sperm can penetrate it.