Entecavir is usually available over the counter but requires a prescription. Entecavir is a guanine nucleoside analog that inhibits the hepatitis B virus polymerase. Chronic adult hepatitis B in the active phase stage can be reasonably treated with entecavir under the guidance of a physician. Entecavir is generally sold in regular pharmacies, but the drug as a prescription drug, need to be prescribed by a professional physician to buy. Entecavir adverse reactions: relevant studies have shown that the most common adverse reactions caused by the drug include physical fatigue, headache, dizziness, nausea and so on. Contraindications: The drug needs to be contraindicated for those who are allergic to the drug and any of the ingredients it contains. Precautions: Some patients experience a severe acute exacerbation of their condition after discontinuing hepatitis B antiviral medication, so patients who stop treatment should be careful to closely monitor liver function. Individuals should suspend medication if lactic acidosis or significant hepatotoxicity occurs by examination during administration. Entecavir needs to be taken on an empty stomach, and try to keep an empty stomach for two hours after taking it, and it is recommended to take it under the guidance of a physician, and not to take the medicine without authorization.