Patients taking entecavir can change their medication to tenofovir, but they must do so under the supervision of their physician and should not change their medication on their own. Entecavir is an antiviral medication that can be used to treat chronic adult hepatitis B. Tenofovir is also an antiviral medication that can be used by adults and adolescents over 12 years of age who have chronic hepatitis B. For patients using entecavir, individuals who experience drug resistance or poor efficacy after taking the medication may change the medication to tenofovir under the direction of their physician, but it is generally not recommended to change the medication if they are experiencing good therapeutic results with entecavir and have not experienced drug resistance. Adverse reactions: whether using entecavir or tenofovir, one may face some adverse reactions, the more common ones are nausea, headache, fatigue, vertigo, etc. Contraindications: whichever drug one is using, it must be contraindicated if one is sensitive to the drug. Individuals who experience some unusual and serious adverse reactions after using the medication must inform their physician promptly. Entecavir and tenofovir are both first-line therapeutic drugs used in the treatment of chronic hepatitis B. It is recommended to follow the doctor’s instructions to use the appropriate medication regimen for yourself, and not to change or stop the medication on your own to avoid delays in your condition.