Viagra generally refers to sildenafil citrate tablets, there is no course of treatment for this product, and it can be taken before sexual intercourse. This product is a short-acting drug, after taking about 1 hour can be effective, in the sexual behavior before taking the drug can be, its half-life is about 4 hours, if the duration of erection time is greater than 4 hours after taking, need to be vigilant about the occurrence of abnormal erection. The drug is a symptomatic treatment drug, there is no clear course of treatment. Taking the drug may cause adverse reactions such as headache, flushing, dyspepsia, back pain, myalgia, nausea, dizziness and rash, and is contraindicated in those who are allergic to the drug. The drug is prohibited in combination with nitrates, and it is also contraindicated in women, children, and people whose recent cardiovascular state does not allow them to have sex. The drug is a prescription drug, it should be taken in strict compliance with medical advice, such as taking other drugs at the same time in the use of sildenafil please consult a physician, in order to prevent drug interactions from occurring.