Information last revised October Stop taking sildenafil and get medical help right away if these effects occur. Terms and conditions of use. Reading is good for you Prolonged erection: If an erection lasts longer than 4 hours a rare occurrence , seek immediate medical assistance. A high-fat meal may reduce the effectiveness of Viagra Sildenafil.In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis to help a man get and keep an erection. This drug does not protect against sexually . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . 28 rows · Viagra: Brand/Generic: $ – $ 25 – 5 – mg: View Product: Cialis: Brand/Generic: $ – $ – 5 – 10 – 20 mg: View Product: Advair Diskus: .