Men are not affected by fertility during treatment with entecavir. Adult males can be treated with entecavir under the supervision of a medical professional in cases of chronic hepatitis B with active replication of the hepatitis B virus, persistent elevation of serum alanine aminotransferase, or histology of the liver showing the danger of active lesions. More retrospective studies in recent years have shown that the incidence of fetal teratogenicity or lethality in most male and female hepatitis B patients taking oral entecavir is not as high as the data in animal studies. In particular, in males, there was no statistical difference between the incidence of fetal teratogenicity on the drug and teratogenicity without the drug. The most common adverse reactions caused by entecavir include headache, dizziness, fatigue and nausea. Entecavir needs to be contraindicated in people who are allergic to the drug. Also patients who stop antiviral therapy for hepatitis B must closely monitor liver function for at least a few months and need to restart treatment if there is a severe acute exacerbation of the disease after stopping treatment.