Viagra generally refers to sildenafil, and the drug can be used by people who have erectile dysfunction of the penis. Sildenafil belongs to a group of selective phosphodiesterase type 5 inhibitors, which can improve the quality of sexual life by improving the hardness of penile erection and other things. The drug is a therapeutic drug and should only be taken by those who have erectile dysfunction. If there is erectile dysfunction, excluding contraindications, you can usually choose to use it under the guidance of a doctor. Adverse reactions to the drug are common, such as headache, dizziness, flushing, increased heart rate. People who are allergic to the drug, people taking nitrate drugs and other people are prohibited from using it, and it should be used with caution if you have heart disease. If there is a disease that requires timely medical attention, the drug should be used under the guidance of a specialized doctor.