Wan Ai Ke is the trade name, generic name of sildenafil citrate tablets, taking this drug for four years ineffective may exist in the drug itself, dosage, personal constitution and other aspects of the reason, need to be specifically analyzed. 1. the drug itself: when taking sildenafil citrate tablets have quality problems, or when using the expiration date has expired, will affect its pharmacological effect, that may lead to take the situation of ineffective. 2. Dosage: The recommended therapeutic dosage of Sildenafil Citrate Tablets is 25~100 mg/dose, taken orally 0.5~4 hours before sexual activity, if the dosage is small or not standardized according to the above requirements, it may lead to the ineffectiveness of the drug after taking. And in the absence of sexual stimulation, the drug does not work. 3. Individual constitution: If the user has low sensitivity to Sildenafil Citrate Tablets or has developed drug resistance after long-term use, or does not meet the indications of the drug (i.e. erectile dysfunction in men over 18 years of age), it may be ineffective after taking the drug. It should also be noted that sildenafil citrate tablets are contraindicated in people who are allergic to it, and also prohibited from combining with nitrate drugs such as nitroglycerin, isosorbide nitrate, and other nitrate drugs, and there may be adverse reactions such as hot flashes (bursts of fever) and headache during the process of using the drug. To sum up, taking sildenafil citrate tablets for four years is ineffective for a variety of possible reasons, the specific must be analyzed under the guidance of a doctor in conjunction with the actual situation of the individual, clear reasons and then make the appropriate medication adjustment. Do not blindly judge, dispose of yourself, so as not to cause adverse consequences.