The main side effects of sildenafil are headache, eye strain, and abnormal erection of the penis. Sildenafil can improve male sexual function. Patients with poor erectile function can be treated by taking sildenafil, after taking it, men’s penis will be easier to erect, and the hardness and duration of erection will be improved accordingly. However, this drug only improves sexual function at the time of taking the drug, and can not completely cure erectile dysfunction. 1. Headache: some patients will have a headache after taking sildenafil, if you have a headache after taking the drug, you need to stop using the drug immediately. 2. Blurred vision: Sildenafil may also cause transient visual trance and hallucinations, at which time the drug should be stopped immediately or replaced with another drug. 3. Abnormal penile erection: some patients taking sildenafil may experience prolonged erection (more than 4 hours) and abnormal erection (painful erection for more than 6 hours), if the erection persists for more than 4 hours, the patient should seek immediate medical attention, otherwise it may lead to permanent loss of erectile function. Contraindications are those taking any dosage form of nitrate, and those who are allergic to any of the components of the product. Sildenafil should be consulted if any discomfort occurs while taking it to avoid delays. The use of this drug must follow the doctor’s instructions, do not blindly use their own medication, so as not to cause adverse consequences.