Viagra, by now as much a metaphor as a medication, could soon face its first real competition for the 15 million to 30 million American men with erectile dysfunction. The trigger: possible Food and Drug Administration (FDA) approval later this year of two drugs that recently entered the European market. Here's how the new choices shape up:

1. Cialis Like Viagra, Lilly Icos's Cialis increases the flow of blood to the penis. Lilly claims Cialis works its magic up to 24 hours; Viagra lasts, on average, from three to four. The French have already dubbed Cialis "le weekend."

2. Levitra First the name: Glaxo-SmithKline and Bayer, bedfellows on this drug, spent a year before settling on a combo of "le," the French masculine pronoun, and "vita," Latin for life. It is effective for nearly five hours, according to the manufacturer; the mechanism is the same as for Viagra and Cialis.

3. Viagra Don't write off the market leader yet. Viagra's greatest strength may be in its track record: 27 studies, conducted over six years on more than 6,600 men, show the original crowd-pleaser is both safe and effective, according to a review published last July in the Archives of Internal Medicine.

4. Herbal Viagra "It's more in the mind," says David Schardt of the Center for Science in the Public Interest, about the efficacy of products claiming to be "natural" sex enhancers. Their numbers are legion, reliable test data are scant, the conclusion is simple: They only get your hopes up.

5. Viagra for women? Drug makers are hard at work on pills, patches and gels to alleviate sexual dysfunctions in women, but no medical treatment, including Viagra, is FDA-approved for women. Most experts agree that a woman's sexuality is too complex for a pill. Unlike a man's, as the success of Viagra shows. Did we need experts to tell us that?

-- Matt McMillen