Viagra can be taken by men of all ages, men with ED, men with high BP, heart diseases, diabetes, and depression. It has been clinically proved to be safe in most men; however, one must not take Viagra if he takes any nitrate medicines. In rare cases, men consuming PDE5 inhibitors (oral ED medicines, which include Viagra) reported a quick fall or loss of vision. The most usual side effects of Viagra are facial flushing, headache, and upset stomach. Rarely, bluish or blurred vision, or sensitiveness to light may occur. However, there is no any medically proven report says that these disorders are directly related to the consumption of Viagra. If you come across any of such side effect, immediately stop using Viagra, and consult with the physician immediately.