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.

To determine if this cell damage actually affected fertility rates, the researchers compared the fertility of two groups of male mice, one of which had been given Viagra. They found that mice in the Viagra group produced 40 percent fewer fertilized embryos than mice that had not been given any drugs.

Researcher David Glenn noted that the many fertility clinics that prescribe Viagra in order to increase sperm counts may actually be harming the fertility of their clients.
“I think it is worrying that some in-vitro fertilization clinics are using Viagra in order to boost fertility results,” Glenn said. “Couples that go there for treatment are, by definition, already having problems getting pregnant. Giving male partners something that could make the problem worse is scarcely the right approach.”
Glenn also expressed concern over the long-term effects that recreational Viagra use might have on people’s fertility.
“Viagra has become a widely used recreational drug,” Glenn said. “It is mixed with cocaine, for example, and is sold in clubs. Our work leaves open the possibility that there could be a cumulative effect from taking Viagra, however, which could pose serious fertility problems in later life.”