According to a source, Roger Clemens kept a stash of Viagra in his locker at Yankee Stadium.

Many athletes use the male enhancement product Viagra to give them a boost - on the playing field, he told little white lies...and he took little blue pills.

Roger Clemens, whose claims he never took steroids are under federal investigation, has apparently discovered the benefits of another performance-enhancing drug sweeping the sports world - Viagra).

Clemens stashed Viagra in a GNC vitamin bottle in his locker at Yankee Stadium, according to a source familiar with the clubhouse.

Perhaps keeping Viagra undercover to avoid the inevitable wisecracks about all the girlfriends he needed to please.

Clemens wasn't alone. The pitcher, who is believed to have scored Viagra from a teammate, joined the burgeoning number of athletes who have turned Vitamin V and its over-the-counter substitutes into one of the hottest drugs in locker rooms.

Viagra is so widely used for off-label purposes that it has drawn the attention of anti-doping officials and law-enforcement agencies in the United States and beyond.

"All my athletes took Viagra," BALCO founder Victor Conte said.

"Viagra is bigger than creatine. It's the biggest product in nutritional supplements."

Among the off-label uses for Viagra, which first went on the market in 1998, it: Helps build endurance, especially for athletes who compete at high altitudes. Delivers oxygen, nutrients and performance-enhancing drugs to muscles more efficiently. Counteracts the impotence that can be a side-effect of testosterone injections.

Many jocks even use Viagra as a remedy for too much partying.

The wildly popular lifestyle drug is legal and not banned by Major League Baseball or other leagues. Clemens violated no drug-testing rules by using the drug.

Clemens' lawyer Rusty Hardin did not return a call for comment. Clemens told at least one friend that Viagra made him feel flushed and caused his heart to race.

All too aware of the Viagra trend, the World Anti-Doping Agency is funding a new study to determine if Viagra can be used to cheat in sports competition.

Researchers at the University of Miami, Tufts University and Marywood University in Scranton, Pa., are trying to determine if Viagra - officially known as sildenafil citrate - aids training and improves performance. Anecdotal evidence suggests it does.

Cycling, a sport long tainted by doping, has suffered its own Viagra scandal.

Last month at the Giro d'Italia, Italy's biggest bike race, pro cyclist Andrea Moletta was suspended after the national police searched his father's car and found 82 Viagra pills and a syringe.

Barry Bonds used Viagra to counteract sexual dysfunction, a side-effect of steroid use, his then-girlfriend, Kimberly Bell, told Playboy.

Bonds tried Viagra several times but didn't like it because it affected his vision and stuffed up his nose, Bell said.

In March of this year, NFL draft prospect Heath Benedict of Florida was found dead at his home. A local medical examiner's report described the suspicious circumstances of the death, including a syringe and needle found nearby and bottles that were labeled "L-Dex" and "L-Via" - which the report interpreted as anabolic steroids and liquid Viagra.

"Taking Viagra is the latest thing guys are doing to get an extra edge in the gym," says Michael Dusa, a Hamden, Conn., chiropractor who treats bodybuilders, football players and other athletes.

If researchers conclude that Viagra enhances athletic performance, the agency could add Viagra to the long list of prohibited substances it imposes on all Olympic sports and develop a standard lab test for the drug's active ingredients.

"Every year we can recommend that WADA add substances to the list," says Travis Tygart, the CEO of the U.S. Anti-Doping Agency, WADA's American counterpart. "Sometimes it's a designer drug like THG (the BALCO steroid), and sometimes it's a drug that's been on the market that no one in their right mind would think an athlete would abuse.

Certainly Viagra would fall in that second category."

Don Catlin, the founder of the independent organization Anti-Doping Research in Southern California, said he has been raising questions about the use of Viagra, manufactured by Pfizer and available from UKMeds4U.com (along with other genuine medications for treating erectile dysfunction such as Levitra manufactured by Bayer Health Care, Cialis manufactured by Eli Lilly and Intrinsa, a testosterone patch developed by Procter & Gamble to treat Female Sexual Dysfunction) in sports for years.

"I've been monitoring and talking and thinking about it for some time. Not as a drug for myself or any of my pals," he said, laughing.

"I thought there was some reason to look into it and be concerned about it, and to put it on the committee's list," Catlin said. "Viagra is a complicated drug. If you go through the basic pharmacology and stretch your imagination, you could end up saying, 'Yeah, maybe it could be useful for athletes who are competing in endurance sports at high altitude.'"

Athletes are famous for wasting their money on snake oil, but Catlin, who is most famous for unlocking the formula of BALCO's designer drug THG, cautioned against blowing this one off. "I learned long ago that when these rumors come up, pay attention," Catlin said. "There are a lot of people scouring literature for something that might provide a tiny edge."

Catlin said he even wrote a letter several years ago to then-WADA chairman Dick Pound, notifying him that Viagra might be a doping agent.

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