Evidence-based academic analysis of sildenafil citrate: mechanism, pharmacokinetics, clinical efficacy, and safety profile. 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. Sildenafil (Viagra) is a tablet that's taken by mouth for erectile dysfunction (ED) in adults. It works as a phosphodiesterase-5 (PDE5) inhibitor to help people get an erection or keep an erection that lasts for sex. Discover the mild and serious side effects of Viagra (sildenafil). Learn how to manage symptoms safely and when to seek medical help. Viagra relaxes muscles found in the walls of blood vessels and increases blood flow to particular areas of the body. Viagra is used to treat erectile dysfunction (impotence) in men. Viagra is used to treat problems relating to male sexual function, particularly problems concerning the ability to achieve and maintain an erection. Learn how to take Viagra safely to treat erectile dysfunction. Swallow a 50 mg dose of Viagra 30-60 minutes before sex. Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more. Learn more about Viagra, including its uses, dosage, side effects, and how to get it. Stop sexual activity and get medical help right away if you get symptoms such as chest pain, dizziness, or nausea during sex. Find patient medical information for Sildenafil (Viagra, Revatio) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings.