Entecavir taking 20 days, whether the effect is obvious can not be generalized, there are some individual differences. Entecavir is clinically used to fight hepatitis B virus infection, it usually takes 1 to 3 months to see the effect, the specific time to see the effect is generally related to the patient’s specific situation. As a drug for hepatitis B, entecavir works by blocking the replication of the hepatitis B virus and regulating the body’s immune function. As we know, the hepatitis B virus cannot be eliminated, so Entecavir tends to take a long time. Common adverse reactions to entecavir include nausea, headache, fatigue, and dizziness, and it is contraindicated for those who are allergic to entecavir components. The use of entecavir carries certain risks and patients are advised that it is necessary to get guidance from a specialist.