NEW YORK (CNNMoney.com) - The glory days of sexual dysfunction drugs may have come and gone.

Everybody knows about Viagra, Pfizer's famous treatment for erectile dysfunction in men. But not everybody uses it.

Viagra, which works by improving blood circulation, was the first drug of its kind when it was launched in 1998, and it quickly reached a billion dollars in annual sales. But Viagra sales growth failed to impress in 2005, and its new competitors -- Cialis from Eli Lilly & Co. and Levitra from Bayer, GlaxoSmithKline and Schering-Plough -- failed to put the spark back in an industry that might have already reached capacity.

In a report issued on Tuesday, Deutsche Bank analyst Barbara Ryan said the erectile dysfunction drug market was hampered by "anemic" growth, despite the recent entry of Cialis and Levitra. Ryan said Viagra commanded 60 percent of market share, with 26 percent for Cialis and 14 percent for Levitra.

"At this point, it's more [a matter of] the three players grabbing share from each other," said Al Rauch, analyst for A.G. Edwards & Sons. "We're not expecting the market to grow substantially."

He explained that the erectile dysfunction drug sector was hard hit by reports in May of 2005 that the drugs may be associated with vision loss. The Food and Drug Administration has not confirmed the reports, but has updated the label on erectile dysfunction drugs to include their information. Analysts have tended to downplay these side effect concerns, since only 38 of the 20 million Viagra patients reported vision problems, with even fewer complaints about Cialis and Levitra.

While erectile dysfunction drug sales have pulled out of the slump that occurred following last spring's blindness reports, they aren't likely to show real growth in 2006, said Rauch. Pfizer's (down $0.01 to $24.54, Research) Viagra sales from 2005 are likely to total $1.6 billion, said the analyst, but based on declining prescription volume he projects a slightly lower tally for 2006: $1.5 billion. Rauch projects modest sales increases for the two newer drugs in 2006: $900 million for Cialis and $350 million for Levitra.

The companies backing these drugs did not offer year-end tallies for 2005. Lilly (up $0.29 to $57.37, Research) said that Cialis sales totaled $526 million in the first nine months of 2005. Bayer (down $0.39 to $43.81, Research), the German maker of Levitra, said its sales totaled $228 million for the first nine months of 2005. In addition, that drug's U.S. marketers, GlaxoSmithKline (up $0.60 to $52.55, Research) and Schering-Plough (down $0.35 to $20.58, Research), together collected a total of $150 million in royalties from that period.

"The market dynamics point to Viagra and Levitra being flattish, and Cialis growing slowly," said Rauch. "None of these drugs are going to be major contributors to the value of these companies in 2006."

In an effort to combat this trend, Pfizer has been ramping up its advertising campaign related to sexual dysfunction. Late last year, the company said it would release new ads "to highlight the unique clinical profile for Viagra." Pfizer spokesman Dan Watts said the company has begun airing "non-branded" television ads that do not mention Viagra but expand awareness of erectile dysfunction, with plans for more Viagra-specific ads in the near future. These are in addition to the Viagra print ads now appearing in newspapers and online.

Watts said that Pfizer is trying to reach out to men with erectile dysfunction who have not been diagnosed or treated. "Even though there's a lot of ads [already] out there, there's a lot of stigma and embarrassment, and these ads are to motivate men to take action" by meeting with their doctors, said Watts.

For those wondering whether they need Viagra, Pfizer's web site offers an online quiz on sexual health, where men are asked questions about erection quality and sexual performance.

But the market may have already peaked, given that the introduction of Cialis and Levitra did not expand it the way many had hoped.

Viagra grabbed the lion's share of sales when it debuted, but the new drugs aren't much different from the old, which is why the market is not expected to radically expand, said Rauch.

"These drugs all work in one mechanism," said Rauch, referring to the chemical action that makes the drugs effective in the human body. "If someone came out with a different type of erectile dysfunction drug there might be potential to expand the ED market, but these three drugs essentially do the same thing."

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To read about slumping drug stocks in 2005, click here.