You can take this medicine with or without food 30 minutes before sex, depending on the dose. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa an inherited eye condition that causes loss of vision or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . Viagra is available in mg, mg, and mg doses and can be purchased in day and day supplies. Shipping is free, and your new medication can be sent . For professionals. Drug Images. What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or .