Continue to take sildenafil even if you feel well. If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. Ask your pharmacist for a list of the ingredients. Some medications should not be taken with sildenafil. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Shake the liquid well for 10 seconds before each use to mix the medication evenly.AdRead Customer Reviews & Find Best Sellers. Free, Easy Returns On Millions Of Items. Know Everything You Need To Know About Health, Mind and Body With Our Books.1M+ visitors in the past month.  · For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual .