Sildenafil may not be safe to take for people with certain medical conditions including: a past history of stroke or heart attack in the last 6 months retinitis pigmentosa an eye disease It can also interact with many other medicines, particularly nitrates used in heart disease , amyl nitrite and blood pressure medicines. If you buy sildenafil for erectile dysfunction, it can also be known by the brand names Viagra, Aronix, Liberize and Nipatra. Sildenafil for pulmonary hypertension can also be known by the brand names Revatio and Grandipam. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. This medication is taken with or without food an hour before sex. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works. Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may also occur. If.