More than a decade Viagra ranks among the best-known brand names on earth. But in recent years, sales of Viagra have been going, well, flaccid.

Cialis is gaining on Viagra, especially outside the U.S. Eli Lilly, manufacturer of Cialis, says its drug is number one worldwide, though Pfizer, manufacturer of Viagra, disputes this. Viagra is still the top-seller in the U.S., but its market share has been slipping.

The reason is that Cialis has a longer duration of action. Taking one Cialis pill, a man gains erection assistance for 36 hours. Viagra and Levitra last for about 4 hours.
In Europe, Cialis is marketed as “the weekend pill.” One dose and a man gets an erection boost for almost three days.

In some published studies, researchers have asked couples to try both Viagra and Cialis. Participants used each drug for two to six months. By the end of all trials, the couples preferred Cialis, typically by ratios of more than two-to-one. The main reason: Its longer duration of action offers greater freedom from sexual time pressure.

Chemically, the three erection medications, Viagra, Cialis and Levitra, are quite similar, with similar side effects. But individual men react differently to them. If you’d like to use one, it’s best to try all three to see which provides the greatest benefit with the fewest side effects.

These drugs work in 60 to 70 percent of older men, but they don’t help about 30 to 40 percent, so don’t be surprised if you notice little or no benefit.

However, even when they work, erection drugs do not not have an effect if you are not sexually stimulated. In addition, erection medications are not aphrodisiacs. They do not boost sexual desire or arousal. They just increase blood flow into the penis. In young men, erection and arousal are typically synonymous. But as men age, erection and arousal become uncoupled, and older men may enjoy drug-fueled erections but not feel aroused.