Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Proper Use Use sildenafil exactly as directed by your doctor. If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on an average dose of sildenafil and increase or decrease your dose depending on your response to the medication. Although not all of these side effects may occur, if they do occur they may need medical attention. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. The effects may be increased because of slower removal of the medicine from the body.Key facts. 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. AdEnjoy Greater Libido & Performance. Fast Express test1.ruries: Various · Best Sellers · Aphrodisiacs · All Products · Ubulawu Dream Herbs.  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. If you take sildenafil for pulmonary arterial hypertension, do not take Viagra® or other PDE5 inhibitors, including tadalafil (Cialis.