The sign on the front door describes the venue as an 'adult shop', a euphemism that adorns the plethora of small sex shops that dot China's capital. But step inside and you'll find a miniature drugstore carrying more than 60 medicines aimed at increasing male virility—each one likely to be a counterfeit.

The medicines—some of which cost upwards of 750 renminbi ($110)—are locked behind a sliding glass door. I ask the store clerk if she sells Pfizer's Viagra, and the young woman, decked out in a nurse's white uniform and hat, reaches into her pocket and pulls out a set of jingling keys.

All nighter: A Beijing 'adult shop'. Credit: Paul Mooney

The pills are blue and appear to have the right markings. But they come in a bottle—and Pfizer doesn't sell Viagra in a bottle in China. The packaging clearly displays Pfizer's logo on the front, but the top flap says the contents were made by 'The US Institute of Biology'. Another telling sign is the blaring words on the front of the packaging, in all-capital letters: LONG-LASTING ERECTION.

Inside the bottles, the 'Viagra' comes in packets ranging from one to six pills each, but Pfizer only distributes the drug in two formats: one- and five-packs. At the sex shop, a pack of four sells for 180 renminbi—less than half the price of Pfizer's locally distributed pills.

When I question the authenticity of the pills, the clerk maintains that the medications are safe, and she pulls out a wide variety of other bottles and boxes, many with American-sounding names including USA Black Gold, American Prolong Time, USA Vermont, USA Super Viagra and American Ji Jie Hao (which has a photo of an American combat soldier).

A few blocks away in another adult shop, there are a wide variety of Chinese erection enhancers, but none with the word Pfizer on them. When I ask for Pfizer by name, the 'nurse' takes out a key and opens the closet door behind her. She rummages through a shoe box and turns around to display a wad of little blue tablets, each stuffed in tiny, individual Ziploc bags. The price sticker reveals that a single pill costs 300 renminbi, far above Pfizer's selling price for the drug in China. “These are imported from the United States,” she insists, adding that Pfizer's China products are made in local factories and so may be unreliable.

There are also a number of Chinese herbal remedies available, but even those may be fakes, and possibly dangerous, according to Fang Shimin, who runs the New Threads blog that exposes scientific corruption in China. “Many makers of TCM [traditional Chinese medicine] products add crushed Viagra to their medicines to make them appear to work,” he says.