Avanafil Stendra. Its effects often last for 4 to 5 hours. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. These are commonly prescribed for an enlarged prostate or male pattern baldness. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Some medications should not be taken with sildenafil.you should know that sildenafil is available under the brand names Liqrev, Revatio, and Viagra. You should only be treated with one of these products at a time. The following nonprescription or herbal products may interact with sildenafil: cimetidine (Tagamet HB), . Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used. Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is approved for this use in males.