Breastfeeding is not recommended for women taking tenofovir because animal studies have shown that tenofovir can be secreted into breast milk, and the risk to nursing children cannot be ruled out. Tenofovir inhibits the replication of the hepatitis B virus and is used clinically for the treatment of chronic hepatitis B. Tenofovir has been shown to be secreted into breast milk in animal studies. Results of animal studies have shown that tenofovir can be secreted into breast milk, but data on the effects of tenofovir on infants are insufficient, but the risk to nursing children cannot be ruled out. Therefore, for safety reasons, breastfeeding is not recommended for women taking tenofovir. Tenofovir should not be used in people who are allergic to the components of this medicine. Use may cause adverse reactions such as headache and dizziness, nausea and diarrhea, fatigue, itchy rash, and joint pain. Tenofovir should be used under the supervision of a doctor.