Viagra is the trade name, generic name of sildenafil citrate tablets, the drug is a prescription drug, need to be in the clinician prescription before you can buy and apply. Sildenafil citrate tablets are mainly used for erectile dysfunction, the corresponding drugs can not be applied casually, itself will be accompanied by certain side effects and harm, must be in the clinician to determine the specific condition, can only be applied under the guidance of the doctor, it is necessary to clinically prescribed, can buy the corresponding drugs, belong to the prescription drugs. The drug may cause headache, dizziness, abnormal vision, nasal congestion, flushing, nausea and vomiting, palpitations (rapid heartbeat, often accompanied by panic), joint pain, and skin rashes. The drug is prohibited for children and women; prohibited during the application of nitrate drugs; prohibited for people with significant abnormalities in the functional status of the heart; prohibited for people with significant abnormalities in the function of the liver and kidneys; prohibited for people who are allergic to the product. In case of obvious headache, abnormal vision, gastrointestinal reaction, abnormal heart rate, blood pressure drop and generalized rash during the use of the drug, it is necessary to consult a doctor in a timely manner, and the treatment should be carried out under the guidance of a clinician.