Some men who take Viagra report an unusually rare set of visual changes capable of lasting up to a week, new research finds. Sildenafil citrate, which is sold under the brand name Viagra, is the most commonly used drug to treat erectile dysfunction (ED), a common condition that affects the ability of men to keep an erection firm enough for sex, according to the Mayo Clinic. The little blue pill works by dilating blood vessels and relaxing smooth muscles in the penis, making it easier to maintain an erection. Results typically last between three and five hours. Viagra has been on the market for more than two decades and when taken properly, is generally regarded as safe with few side effects. But when taken under certain circumstances, the drug may cause extreme sensitivity to light, dilated pupils, and intensely colored blue vision tinged with red and green color blindness. That was the case in 17 otherwise healthy male patients who checked themselves into Dünyagöz Adana hospital in Turkey. Each man had taken sildenafil for the first time and at the highest recommended dose of 100 milligrams, yet none of them had been prescribed the drug by their doctor. Treating doctors monitored the patients’ overall health and conducted eye exams before their visual symptoms eventually waned 21 days later. The findings are published in Frontiers in Neuroscience. "Many men use non-prescription performance-enhancing drugs to help with sexual anxiety and erectile dysfunction," said treating physician Dr Cüneyt Karaarslan in a statement. "For the vast majority of men, any side-effects will be temporary and mild. However, I wanted to highlight that persistent eye and vision problems may be encountered for a small number of users." It could be that such vision impairment is the result of an inability to break down and properly eliminate sildenafil from the body, leaving higher concentrations in the bloodstream for longer periods of time. Karaaslan adds that first-time users should start taking sildenafil at a lower dose and always at the discretion of their doctor. "Although these drugs, when used under the control of physicians and at the recommended doses, provide very important sexual and mental support, uncontrolled and inappropriate doses should not be used or repeated," concluded Karaarslan. Viagra is the most commonly prescribed treatment for erectile dysfunction. PaulSat/Shutterstock Source