Viagra, whose generic name is sildenafil citrate, is a common medication used to treat erectile dysfunction in men. Sildenafil Citrate works to treat erectile dysfunction. Adverse effects of Sildenafil Citrate are headache, indigestion, flushing, nasal congestion, muscle pain, nausea, vomiting, dizziness, and rash. Contraindications of sildenafil citrate mainly include those who are allergic to the product are prohibited; during the application of nitrate drugs and guanylate cyclase agonists and other drugs, this drug should be prohibited; within the last half a year, patients with shock, myocardial infarction, and other serious medical conditions, should be prohibited from using this drug. There is a lack of information on the safety and efficacy of controlled clinical trials in patients with pigmented retinitis, heart failure and other diseases, and such patients must use the drug with caution. The precautions of sildenafil citrate are that when used in the treatment of erectile dysfunction, a thorough examination should be carried out; this drug promotes circulating vasodilatation, which may increase the blood pressure lowering effect of other anti-hypertensive medications; during the application period, in case of abnormal erection (erection for more than 4 hours), medical attention should be sought at the earliest possible time. For patients, before applying the drug, it is necessary to go to a specialized hospital and follow the doctor’s instructions for medication. Any adverse reactions should also be treated by a doctor as soon as possible.