Symptoms & causes Diagnosis & treatment Doctors & departments Care at Mayo Clinic Diagnosis Erectile dysfunction FAQs Urologist Tobias Kohler, M.D., answers .Sildenafil usually should not be taken more than once every 24 hours. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. What, if anything, seems to worsen your symptoms? What special dietary instructions should I follow? It works for up to 36 hours. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. What, if anything, seems to improve your symptoms?The Savings Offer and Program expire on 12/31/ For further information, call , visit , or write: Viatris Inc., P.O. Box , Mission, KS . Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or .Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. More Information Erectile dysfunction dietary supplements Coping and support Whether the cause is physical, psychological or a combination of both, erectile dysfunction can become a source of mental and emotional stress for you and your partner. If medication is prescribed, is there a generic alternative? What you can do Take these steps to prepare for your appointment: Ask what you need to do ahead of time. Take sildenafil exactly as directed. What will that cost, and will the visit be covered by my insurance?