Because the erectile-dysfunction drug increases and improves the blood circulation, Endres believes it will help players cope with the thin air of La Paz.

"I had this illumination by reading a magazine, which wasn't a medical one: so we decided to elaborate this topic with a scientific test, and now we shall also give an indication to the technical commission," he said.

Viagra is not a prohibited substance on FIFA's list of banned drugs, but rumors of its performance-enhancing benefits -- in sports -- during the 2008 Olympic Games has spurred research on its doping effects.