Although it's unlikely to be incorporated into the ubiquitous marketing campaigns for erectile dysfunction drugs, a significant off-label use of the medications may have been identified by researchers at Cedars-Sinai Medical Center in Los Angeles. In a laboratory study conducted on rats, the research team used erectile dysfunction drugs to increase the amount of a chemotherapy drug that was able to cross the blood-brain tumor barrier and thus attack the tumor — without affecting healthy brain tissue.

The normal blood-brain barrier serves a salutary purpose, protecting the brain from infections by preventing bacteria in the bloodstream from entering the brain, but the blood-brain tumor barrier hampers the effectiveness of anti-tumor medications by blocking transport of the drugs into tumors.

"We chose adriamycin for this study," explained lead researcher, neurosurgeon Keith Black, "because it is one of the most effective drugs against brain tumor cell lines in the laboratory but it has very little effect in animals and humans because it is unable to cross the blood-brain tumor barrier."

Although Viagra commands more than 60 percent of the ED drug market , which totaled $2.7 billion in worldwide sales in 2006, it turns out that Levitra — which ranks a distant third among the three ED drugs currently on the market — was more effective than the market leader at breaching the blood-brain tumor barrier. "The combination of vardenafil [Levitra] and adriamycin resulted in longer survival and smaller tumor size," said Black. (The study was not funded by the makers of either Viagra or Levitra.)

Control-group rats with brain tumors survived 29 days, while those treated with only vardenafil or only adriamycin survived longer. Those treated with a combination of the two drugs, however, lived longest of all — 53 days — allowing the rodents to "get back in the game" nearly twice as long as their peers in the control group.