Viagra generally refers to sildenafil, no reaction to take this drug may be caused by no sexual stimulation, improper drug taking or serious condition. 1. No sexual stimulation: according to the relevant authoritative information, if the patient follows the doctor’s instructions to take the recommended dose, in the absence of sexual stimulation, sildenafil can not play the corresponding effect, so there will be no reaction after the use of the drug. 2. Improper drug taking: If the patients take insufficient dosage of the drug, the effect will not be achieved. Secondly, since based on the fact that sildenafil is tolerable to human body, the lack of response after taking sildenafil may be related to the long-term use of the drug. 3. Serious condition: In addition, if the primary condition is serious, there will be no response after taking sildenafil. At this time, other treatment modalities need to be considered, such as vacuum erection device therapy and surgical treatments such as introduction of vascular surgery and penile prosthesis implantation surgery. All in all, when the patient has no therapeutic effect with the medication, he/she needs to go to the hospital to clarify the exact cause. The medication should be applied under the guidance of a doctor.