Generic Viagra (sildenafil) belongs to a class of medications called phosphodiesterase inhibitors, which work by increasing blood flow to the penis during sexual activity, resulting in an erection.
Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women. It works best on an empty stomach. Keep in mind that high-fat foods can interfere with Viagra, resulting in it taking longer to work. Take the pill about 30 to 60 minutes before sex. It usually stays active for about four to five hours. However, it can sometimes last eight hours or more.