Viagra is a PDE5 inhibitor, the common name for phosphodiesterase inhibitors, currently on the market are mainly sildenafil, vardenafil, tadalafil three. Sildenafil trade name Viagra, domestic called Jingo, is the earliest used in the clinical drug, it is before sex, 30-60 minutes oral 50mg, the maximum amount of not more than 100mg, easy to be affected by alcohol, greasy food shorter duration of action. Vardenafil is currently less used in the market. Tadalafil trade name cialis is a long-acting Viagra, which is not affected by alcohol, greasy food. The usage of Viagra is mainly on demand, or as scheduled. It cannot be combined with nitrate drugs, which is contraindicated, and should be used with caution for patients with glaucoma and coronary artery disease.