Viagra generally refers to sildenafil, and before taking it, you should check the drug’s instructions and use it as directed, which generally means that you start taking it about 30 minutes or so before intercourse. Sildenafil is generally taken 30 minutes to 2 hours before sex and is characterized by a hard erection but a shorter effective time of about 4 hours. Taking time-delaying drugs may cause adverse reactions such as headache, back pain, indigestion, etc. They should be used under the guidance of a doctor to avoid frequent and excessive use of this type of drug. In addition, it should be noted that the drug to avoid and nitrate drugs at the same time, otherwise it is easy to induce a sudden drop in blood pressure leading to the occurrence of shock. In the use of medication, must follow the doctor’s instructions, rational application of drugs, do not arbitrarily use drugs, to avoid causing serious side effects and adverse reactions.