Viagra, a little blue pill made by the pharmaceutical company Pfizer Inc., became the first oral medicine approved for male impotence by the U.S. Food and Drug Administration. Its approval in March 1998 set off a worldwide demand and sent Pfizer stock soaring. Hardly a day went by when newspapers, radio, and television did not have stories of the Viagra craze. The pill, which sold by prescription for about $10 apiece retail, was taken by men with sexual problems about an hour before they expected to have sexual activity. Their performance during the sex act improved dramatically. The drug, chemically named sildenafil, had been used unsuccessfully as a medicine for heart problems. When some heart patients reported to doctors they were getting erections after taking the pill, it was developed to treat sexual impotence.

Clinical studies of about 4,000 men with erectile dysfunction showed that up to 72 percent reported they...