Based on my understanding of the mechanism by which Viagra works its magic on men, all that would happen in a woman is increased blood flow to the genitals. Perhaps the knowledge of having taken a "sex pill" is enough suggestion to enhance the experience, but no large-scale, controlled pharmacological tests have been done to show any effect in females. Pfizer tested doses of Viagra in female rats and rabbits for carcinogenicity, impairment of fertility, and problems in pregnancy, but failed to find evidence of any detriment. Viagra is listed by the FDA as a Pregnancy Category B drug, which means "animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women." However, it would be difficult to extrapolate the results of these studies to human females without getting flak from scientists, government, and the media.

At any rate, Viagra is not indicated for women and it is not prudent to take someone else's medication.

[Source for pregnancy categories of drugs: http://en.wikipedia.org/.../...y_(pharmaceutical )]