Rarely reported side effects include: an erection that will not go away priapism. Injury to the penis during surgery or radiation, especially during treatment of prostate, colon-rectal, or bladder cancer, hinders your ability to get and maintain an erection. Brand names Why is this medication prescribed? This medicine comes with a patient information leaflet. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription.Last updated on Uses. Warnings. Before taking. Dosage. Side effects. Interactions. FAQ. What is Viagra? Viagra relaxes muscles found in the walls of blood . Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision. About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when.