Sildenafil tablets are mainly used to treat erectile dysfunction of the penis. Usually, patients are able to prolong the duration of intercourse by 20-30 minutes after taking Sildenafil tablets, but the exact duration also varies from person to person and varies from body to body. In addition, sildenafil also has some side effects, which are generally transient and mild to moderate in nature, the incidence of which increases with the dose. The side effects are mainly the following: 1. respiratory system: symptoms such as difficulty in breathing, phlegm, cough, etc. may occur; 2. digestive system: symptoms such as nausea, vomiting, indigestion, diarrhea, etc. may occur; 3. skin and its appendages: flushing, rash, hives, etc.; 4. Nervous system: headache, dizziness, insomnia, ataxia, drowsiness, etc. may occur; 5. Cardiovascular system: hypotension, arrhythmia, heart failure, etc. may occur, mostly during and just after sex; 6. Other: in addition to the abnormal manifestations of the above systems, systemic symptoms such as facial edema, photosensitivity reactions, blood and lymphatic system, metabolic and nutrition, skeletal and muscular system, genitourinary system and so on can also appear some side effects. If these symptoms occur before the start of sexual intercourse after taking sildenafil tablets, sexual activity should be stopped and medical attention should be sought immediately to avoid further damage. In addition, patients should note that if they are allergic to sildenafil tablets or are taking nitroglycerin, sodium nitroprusside or other drugs containing nitrates, sildenafil tablets should be prohibited to avoid adverse symptoms such as sudden drop in blood pressure.