Does Viagra Improve Athletic Performance?

Chicago Bears wide receiver Brandon Marshall says he's heard of NFL players using a surprising drug as an on-the-field performance enhancer: Viagra.

"… it is such a competitive league, guys try anything just to get that edge," Marshall said, via Brad Biggs of the Chicago Tribune, when asked about an apparent increase in NFL suspensions related to the ADHD drug Adderall. "I'm fortunate enough to be blessed with size and some smarts to give me my edge. But some guys, they'll do whatever they can to get an edge. I've heard of some crazy stories. I've heard [of] guys using like Viagra, seriously."

On the face of things, Viagra, the well-known erectile dysfunction medication, would seem like an unusual addition to a doping athlete's regimen.   

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But if what Marshall heard is true and NFL players are using it to boost their game, their strategy may have at least some scientific basis.

Sildenafil citrate, the active chemical in Viagra, works by inhibiting an enzyme that controls blood flow in specific parts of the body. One of these parts is the penis and another is the pulmonary system, or lungs. [7 Surprising Reasons for Erectile Dysfunction]

This is why Viagra and Revatio, a drug prescribed to combat pulmonary hypertension (high blood pressure in the arteries of the lungs), are in fact just two names for the same substance.

Even healthy people can start to experience some of the fatigue associated with pulmonary hypertension when they travel to very high elevations, where available oxygen wanes and blood vessels in the lungs constrict. Multiple studies have shown that sildenafil can help to reverse this effect, improving oxygen delivery to muscles and offsetting the usual drop in endurance associated with high altitude.

So a Viagra or two would likely help Everest climbers stay strong during the trek. But the highest NFL stadium, in Denver, is at just about 5,280 feet (1,600 meters). Could Viagra-popping players be gaining an endurance advantage at that altitude?

A Stanford University study published in 2006 in the Journal of Applied Physiology found that in oxygen-deprived conditions simulating an altitude of 12,710 feet (3,874 m), sildenafil lowered times by a collective 15 percent among 10 trained male cyclists who performed 3.7-mile (6 kilometers) time trials. But researchers realized the study's participants fell into two groups, four cyclists who responded strongly to the sildenafil and six who showed very little change in performance. Among the "responders," times improved by 39 percent compared to a sildenafil-free performance.

In the past few years, researchers at the University of Miami tried to replicate the results of the Stanford study with a pair of trials that included more participants, this time both men and women, and a wider range of altitudes. In the first trial, a field of 20 male and 15 female athletes did cycling time trials at the same simulated altitude as the cyclists in the Stanford study. Only a single male demonstrated a meaningful improvement in his time-trial time after taking a dose of sildenafil.   

"We tested close to 60 trained men and women across our two studies and found no clear benefits at altitudes ranging from 2,100 to 3,900 meters [6,890 to 12,795 feet] simulated altitude," Kevin Jacobs, an associate professor in the University of Miami's department of kinesiology and sports sciences, wrote in an email to Life's Little Mysteries. "It appears from previous work that sildenafil has more consistent benefits at very high altitudes, above 4,300 meters [14,100 feet]."

The stark discrepancy between the Stanford and Miami studies, said Jacobs, might owe to the way participants were selected. Jacobs has consulted with Anne Friedlander, a scientist who worked on both the Stanford and Miami studies, and he believes the Stanford study may have attracted some participants who self-selected based on past difficulties with high-altitude cycling. (The cyclists may have hoped, Jacobs speculated, that the study would help them find the root of their problem.)

This could have confounded the results, said Jacobs, because people who experience unusually pronounced debilitation at high altitudes are much more likely to see benefits from sildenafil. This is why the "responders" (those who benefited from sildenafil) in the Stanford study were not much faster than the "nonresponders" in the high-altitude time trials.

Instead, the responders were much slower at high altitudes when they didn't have sildenafil, and when they did, the whole field showed similar times. This implied that sildenafil didn't supercharge responders' performance so much as it corrected a high-altitude handicap; it normalized them.

Jacobs said the research to date has led him to believe that less than 10 percent of the general population would classify as a responder, someone who could significantly benefit from sildenafil at altitudes similar to the one in the Stanford study. And because the Miami studies showed no benefits from sildenafil at an altitude of 6,890 feet (2,100 m), higher than the highest NFL stadium, Jacobs said he doesn't think it's likely that football players using the drug would gain anything but a psychological advantage on the field.

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