Entecavir is an antiviral drug recommended by several national and international guidelines for the treatment of hepatitis B. Almost all patients have been taking entecavir orally for more than 10 years without complaining of significant discomfort. Early adverse reactions to entecavir include dizziness and gastrointestinal reactions. Long-term adverse reactions are mainly the possibility of viral mutation, leading to treatment failure. If oral entecavir has been taken for more than five years without viral mutation, the probability of further mutation is almost zero. Because entecavir is so effective and has so few adverse effects, guidelines around the world use the drug as a first-line treatment against the hepatitis B virus. In addition, patients should go to the hospital if there is any discomfort, adjust the dosage of the drug or change the anti-hepatitis B virus drug under the guidance of the doctor, and do not stop taking the drug without authorization.