Viagra generally refers to sildenafil citrate, and men who apply this drug sensibly as needed do not experience after-effects. However, after using the drug, some men may experience adverse reactions such as digestive discomfort, allergies, and dizziness. Sildenafil citrate is mainly used to treat erectile dysfunction in men. Regular application of this drug as needed usually does not produce any sequelae. However, after the use of the drug, some patients may experience digestive discomforts such as nausea, diarrhea, dyspepsia, allergic reactions such as rash, itchy skin, and also occasional adverse reactions such as dizziness and visual abnormalities. It should be noted that the application of this drug is prohibited during the application of guanylate cyclase agonists and nitrate drugs; those who are allergic to this drug are prohibited from applying it; patients with cardiovascular and cerebral vascular diseases, sickle cell anemia and other diseases should be cautious of using this drug. Although the application of this drug basically does not produce sequelae, but the corresponding medication program, need to follow the doctor’s instructions, such as the emergence of obvious adverse reactions, should also be as early as possible to seek medical attention.