Women, the maker of Viagra has found, are a lot more complicated than men.

After eight years of work and tests involving 3,000 women, Pfizer Inc. announced yesterday that it was abandoning its effort to prove that the impotence drug Viagra improves sexual function in women. The problem, Pfizer researchers found, is that men and women have a fundamentally different relationship between arousal and desire.

For men, arousal almost always leads to desire. So by improving a man's ability to have erections, Viagra measurably affects his sexual function. But arousal and desire are often disconnected in women, the researchers found, to their consternation.

Although Viagra can indeed create the outward signs of arousal in many women, that seems to have little effect on a woman's willingness, or desire, to have sex, the researchers said.