The side effects of thymidine injection are mainly divided into local reactions and systemic symptoms. Local reactions are redness and swelling at the injection site or temporary muscle atrophy, etc.. No special treatment is needed and will disappear in a short time. Systemic side effects include nausea, fever, dyspnea, elevated alanine aminotransferase, allergic reaction, etc. Common specific side effects are as follows: 1. Local reactions: Some patients will have redness, swelling, discomfort or transient muscle atrophy at the injection site, as well as joint pain and skin rash. Local symptoms will subside in a short time, so there is no need to worry too much; 2. Systemic symptoms: some patients with chronic hepatitis B will occasionally experience temporary elevation of serum transaminase level after using thymidine, and a few patients will experience nausea, fever and drowsiness. Some patients may be allergic to thymidine and have allergic reactions after using it, and serious cases may have hypersensitivity reactions leading to shock. When there is an emergency, you should go to hospital immediately to avoid danger. In addition, thymidine exerts its therapeutic effect by enhancing the immune function of patients, so it is not recommended for patients who are receiving immunosuppressive treatment, such as organ transplant recipients, and liver function should be checked regularly during treatment.