However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Ask your doctor if you have any questions. By controlling the enzyme, sildenafil helps to maintain an erection after the penis is stroked. You may take this medicine with or without food. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse.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 . 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 .  · Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines .