Pfizer Inc. (PFE), the drug’s producer, now has a site for you: its own Viagra.com, where you can get the blockbuster impotence fighter without wondering what shady source you’re dealing with. Using CVS Caremark Corp. (CVS) to verify prescriptions and fulfill orders, the site is Pfizer’s latest attempt to fight counterfeiting. In its announcement this week, the world’s largest drug maker cited a 2011 analysis it did of pills bought from 22 sites ranking high in search results for “buy Viagra.” About 80 percent were fake, containing only 30 percent to 50 percent of the drug’s active ingredient, sildenafil citrate. The new site is a reminder of the original value of consumer branding: as a guarantee of quality. It’s also evidence of the failure ― and the perverse effects ― of online drug regulation.