Can Viagra enhance athletic performance?

If, as the Rolling Stones once proclaimed, a little yellow pill is mother's little helper, what is the little blue pill for Daddy?

We know the little blue wonder pill as Viagra, and its primary use is to improve a man's function in one particular environment. But can it also enhance athletic performance in baseball, particularly when used in combination with anabolic steroids? This is the latest question being asked after a New York Daily News report linked Roger Clemens to Viagra, citing a "source familiar with the clubhouse" as saying the pitching ace kept the "clearly marked, diamond-shaped pills" in his locker.

So is there any validity to the notion that Viagra could be used to enhance athletic performance? As is typical in the medical world, there is no simple black-and-white answer. We do know that no definitive, well-controlled, randomized clinical trial studies exist that have specifically examined the effects of sildenafil -- the active ingredient in Viagra -- on athletic performance.

Before considering how Viagra might be linked to sports, it is important to understand how the drug works. Simply put, Viagra is a vasodilator, meaning it helps relax blood vessels to allow for increased blood flow. In the presence of sexual stimulation, this increased blood flow is the means of counterattack against erectile dysfunction. Such increased blood flow is not as helpful during competitive sports. Scientific studies have shown, however, that the vasodilation effects of Viagra also can improve blood flow to the lungs. This can have a positive effect on conditions in which the blood pressure is elevated in the arteries that supply the lungs, also known as pulmonary arterial hypertension.

How does that relate to athletics? Naturally, one has to start by looking at scenarios in which minimized lung capacity could be a limiting factor. Everyone can appreciate that a high-altitude environment seriously affects the workload on an athlete's lungs because of the decreased availability of oxygen. Cyclists who traverse mountain ranges, marathoners who run courses in high elevations and winter-sport athletes such as competitive cross-country skiers all participate in some form of altitude training as a means of conditioning for their environment.

But what about sports such as mountain climbing in which the altitude itself presents the biggest physical challenge? Pulmonary hypertension then can become one of the most significant barriers to completing an event. This is where it gets interesting. Several studies have looked at the effect of Viagra in a hypoxic (low-oxygen) situation and have found that the drug improves performance by improving exercise capacity (as measured by a number of variables -- such as cardiac output -- that determine how hard the heart has to work to perform exercise tasks). A 2004 study in the Annals of Internal Medicine showed improved exercise capacity in a group of climbers measured at the base camp of Mt. Everest (elevation 17,600 feet above sea level).

Dr. Robert Nied, a sports medicine physician at Kaiser Permanente in Santa Rosa, Calif., emphasized that the studies thus far that have found improved performance with the drug were done only at extremely high elevations at which oxygen levels were seriously diminished or in laboratory environments that replicated extreme-altitude hypoxic environments. Nied explained that studies attempting to establish the presence of performance improvements at normal elevations found no such benefit. This is critical because the highest elevation in baseball stadiums is 5,200 feet (Coors Field), and that doesn't even begin to approach the 12,000-plus feet of elevation environments used in these studies. So although the thinner air at Coors Field may allow the baseball to travel farther, it does not appear that the little blue pill would play a role in improving an athlete's performance at that stadium or any other. In fact, a study published in the Journal of Applied Physiology in 2006 suggests the effects of the drug eliminate a decrease in performance (due to low-oxygen environments) but don't provide enhancement beyond normal. Simply said, as far as exercise capacity, the drug could be considered a treatment in response to the effects of high altitude as opposed to an ergogenic, or performance-enhancing, aid.

But besides potentially counteracting the effects of altitude, how does lung-capacity improvement help a baseball player? It doesn't really, because playing baseball does not rely on aerobic endurance as a variable for success. There have been some suggestions that the vasodilation effects of Viagra could improve the effect of anabolic steroids if taken together, but no real medical basis has proven that to be true. Viagra's vasodilation effect is fast-acting; it has a quick onset (as soon as 30 minutes) and is removed from the bloodstream within hours. The anabolic steroid effects of increased testosterone, on the other hand, are not available immediately, and steroids work via an entirely different mechanism of protein synthesis at the cellular level, not via arterial blood flow.

Dr. Gary Green, a clinical professor in UCLA's division of sports medicine and adviser to Major League Baseball on anabolic steroids, says he has not specifically heard of athletes' combining Viagra with anabolic steroids. But he is aware of over-the-counter supplements such as NO2 -- whose main component is an arginine compound purported to increase nitric oxide levels and therefore increase blood flow, effects similar to the effects of Viagra -- being used in conjunction with steroids. Green is quick to point out that scientific studies have shown there is no benefit from this combination, but he also adds that the placebo effect in athletes can be quite strong, and if they firmly believe that something is helping them, their performance can, in fact, improve.

Athletes could be saying they take [Viagra] for one reason to cover up the real reason.

--Dr. Gary Green

And what about the notion that steroid use can lead to impotence, and that an athlete might seek to take Viagra to counter such effects? Nied says most short-term steroid users don't experience erectile dysfunction. Instead, as a result of the increased testosterone, they demonstrate an increased sexual drive. Long-term steroid users, however, may eventually suffer sexual side effects when they cycle off the drugs. Steroids suppress the body's natural testosterone production, so the phrase "use it or lose it" comes into play: The testicles, having not been called into action to produce the hormone during the use of synthetic steroids, atrophy as a result. Once the steroids are no longer present, the body is not as capable of manufacturing its own hormone, leaving these individuals potentially in search of some sort of medicinal aid. Green says the No. 1 reason athletes who take anabolic steroids seek a Viagra prescription is for impotence associated with the steroid use. With or without steroid use, taking Viagra to treat erectile dysfunction is not something every athlete wants to openly acknowledge. Adds Green, "Athletes could be saying they take [Viagra] for one reason to cover up the real reason."

As will no doubt forever be the case in sports, some athletes will try to gain an unconventional competitive edge, be it through drugs or other means. Viagra is not currently listed as a banned drug in sports, although eventually that may change. The World Anti-Doping Agency is concerned enough about the potential abuse of Viagra in cycling that it is funding a study, currently under way at the University of Miami, examining whether the drug can improve the performance of cyclists who are riding at altitude. Given that cyclingnews.com reported last month that Italian cyclist Andrea Moletta was suspended after a police search of his father's car at the Giro d'Italia turned up 82 Viagra pills and a syringe hidden in a tube of toothpaste, the Agency may be on to something.

Even then, think of the challenges that could arise with testing. According to Green, all sports agencies have some measure of "therapeutic use exemption," whereby an athlete can use an otherwise-banned substance if it meets that agency's criteria for therapeutic use. Such criteria typically include the presence of a "significant health effect if the substance is not used" and the lack of any safe alternative. Insulin (used by patients with diabetes), for example, is listed as a banned substance by the World Anti-Doping Agency. It is easy enough to see how the arguments for therapeutic use exemption for insulin can be reasonably made. But Viagra? One can only imagine how fraught with complications that scenario could become.

In the meantime, no current evidence suggests that Viagra can enhance performance in baseball or any other sport. Nor is there any evidence to support the idea that Viagra and anabolic steroids, when taken together, enhance or accelerate steroid delivery. Be that as it may, history demonstrates that some athletes will continue to seek out new and different methods of performance enhancement, whether or not the science supports those methods. After all, as Green points out, the first definitive study showing the muscle-building effects of testosterone was not published until 1996, but athletes have been using testosterone for such a purpose since at least the 1950s. At least for now, medicine tells us that the benefits of the little blue pill can be realized only in the bedroom, not in the locker room.

Stephania Bell is an injury expert for ESPN.com. She is a physical therapist who is a board-certified orthopedic clinical specialist and a certified strength and conditioning specialist.