Viagra, generally referred to as sildenafil, is used once every three days and is generally not very harmful to a man’s health and function. Sildenafil is indicated for patients with erectile dysfunction. Taking the drug once every three days is a more appropriate frequency of use and generally does not cause serious harm to the body. However, it may cause headache, facial flushing, indigestion and other adverse reactions; but they are mild and not long-lasting, and will disappear soon. The contraindications of sildenafil are patients taking nitrate drugs, as well as patients who are allergic to sildenafil, and the use of sildenafil during the period of taking nitrate drugs will cause patients to have low blood pressure, which can be life-threatening in serious cases. When using sildenafil, you should also pay attention to not drink alcohol at the same time, because alcohol will seriously affect the erectile efficacy of sildenafil. Sildenafil is for adult use and should not be purchased or used by minors under the age of 18. In addition, women, allergic to the product and other people should also be prohibited. If you experience significant adverse symptoms after using Sildenafil, you should seek medical attention.