Sildenafil ( Viagra ) significantly improved the cardiovascular and exercise performance measures of trained cyclists at high altitude, mostly because the drug helped some participants improve a lot ( up to 45% ) while others showed little change.
Sildenafil provided no benefit at sea level.

Ten cyclists who took Sildenafil at altitude collectively lowered the time it took to cover six kilometers by 15% compared to placebo trials at altitude.
The cyclists also significantly improved stroke volume and cardiac output compared to the placebo trial.
Sildenafil also minimized the decline of arterial oxygen saturation of the arteries when the cyclists were at simulated altitude of 12,700 feet.

But the researchers discovered that these improvements occurred largely because some people achieve major gains with Sildenafil at altitude while others improve much less or not at all. The responders improved 39% in the time trial performance at altitude compared to their performance at altitude with a placebo. Some in the responder group improved as much as 45%.

Non-responders improved an insignificant 1%.

Source: American Physiological Society, 2006


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