Some 55 percent of erectile dysfunction (ED) drugs such as Viagra sold over the Internet are counterfeit, according to a study by major pharmaceutical firms.

The study found that out of the 184 drug orders, 102 -- or 55 percent -- were fake. Drugs ordered from sites located in Japan were 44 percent counterfeit, while 68 percent from Thailand came up fakes. Some of the counterfeits contained twice the proper amount of the active pharmaceutical ingredient and others had none at all, while several impurities were also detected.