Sildenafil is a prescription drug that can be taken on an as-needed basis or on a regular basis, depending on the patient’s condition. 1. As needed: clinically used in the treatment of erectile dysfunction is taken as needed, about 2 hours before sexual intercourse. It can improve the hardness and duration of erection during sexual intercourse. 2. Take it on time: If used for the treatment of pulmonary arterial hypertension, it needs to be taken on time, according to the doctor’s adjusted dose every day on time, and can not casually adjust the dose and stop taking the drug. Overall, sildenafil is a prescription drug, after using the drug may appear nausea, vomiting, headache and other symptoms, and can not be used together with nitrate antihypertensive drugs. Sildenafil needs to be taken under the guidance of a professional doctor and should not be taken blindly.