For Pfizer, that's a big problem. People who buy fake drugs online that don't work, or worse, harm them, may blame the company's product. That's because it's virtually impossible to distinguish fakes from real Viagra.
"The vast majority of patients do believe that they're getting Viagra," says Vic Cavelli, head of marketing for primary care medicines at Pfizer.
The sales lost to counterfeits threaten Pfizer at a time when Viagra already is losing is dominance in the market.
Pfizer invented the term "erectile dysfunction" to replace the less-palatable medical term "impotence" after it came up with the first drug for the condition. It was a lucky find. Pfizer was testing an experimental blood pressure drug when older men in the study started telling research staff about an unexpected but welcomed side effect: better erections.
Pfizer quickly developed Viagra and made the discussion about erectile dysfunction mainstream with ads featuring ex-Sen. Bob Dole and other public figures.
But Viagra's share of the $5 billion-a-year global market for legitimate erectile dysfunction drugs has slipped, falling from 46 percent in 2007 to 37 percent last year, according to health data firm IMS Health.
The reason? Competition from rival products, mainly Eli Lilly and Co.'s Cialis â¿¿ the pill touted in those ubiquitous commercials featuring couples in his-and-hers bathtubs in bizarre places.
Judson Clark, an Edward Jones analyst, forecasts that Viagra sales will decline even further, about 5 percent each year for the next five years, unusual "for a drug in its prime."
Clark says he thinks Pfizer's strategy will prevent sales from declining, but he's unsure how well it will work.
"It's a very interesting and novel approach," he says. "Whether it returns Viagra to growth is hard to say."
On the Net:
Link to accredited pharmacies: http://www.nabp.net/programs/accreditation/vipps/find-a-vipps-online-pharmacy
Linda A. Johnson at http://twitter.com/LindaJ_onPharma