What special dietary instructions should I follow? Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Vardenafil usually works for 4 to 5 hours. What side effects can this medication cause? The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. Do not start these medications while taking sildenafil without discussing it with your healthcare provider.The Savings Offer and Program expire on 12/31/ For further information, call , visit , or write: Viatris Inc., P.O. Box , Mission, KS . 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 . 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 .