Viagra refers to Sildenafil Citrate Tablets, which can increase the blood flow to the cavernous body of the penis and enhance the strength of the erection, and is a drug for the treatment of erectile dysfunction in men. Sildenafil Citrate Tablets have no effect, you need to adjust the way of medication under the guidance of a doctor according to the specific situation, such as drug dose and medication time, or for the primary disease. 1, adjust the way of medication: in most cases, Sildenafil Citrate Tablets need to be given a starting dose by a professional doctor, if the dose of medication is too small, it may lead to no effect. The dosage of the drug can be increased appropriately according to medical advice and needs to be subjected to adequate sexual stimulation to ensure its effectiveness. The plasma peak concentration is reached in 30-120 minutes when taken orally in fasting state. If taken with high-fat diet, the absorption rate may be reduced, so the drug is usually taken 30-60 minutes before intercourse for better effect; 2. Treatment of primary diseases: If one suffers from organic diseases such as penile vascular malformation and penile arteriovenous fistula, taking sildenafil citrate tablets may not have obvious effect. Surgical treatment can be carried out to repair the damaged blood vessels of the penis, or take the surgical treatment of penile prosthesis implantation to maintain the normal sexual ability of the patient. If taking sildenafil citrate tablets has no effect, it is recommended to visit a hospital, improve the relevant auxiliary examinations, exclude pathological factors and take medication under the guidance of a doctor. If there is organic lesion of the penis, relevant examination and treatment should be carried out in time.