Long-acting penicillin is harmful to the body, mainly for allergic reaction, secondary infection and penicillin encephalopathy. 1. Allergic reaction: some patients will have an allergic reaction to penicillin drugs, which may even cause anaphylactic shock in severe cases, and may lead to the death of the patient if not rescued in time. 2. Secondary infection: long-term use of penicillin may lead to the emergence of drug-resistant bacteria in the patient’s body, such as penicillin-resistant Staphylococcus aureus. Drug-resistant bacteria may lead to secondary infections in patients, causing aggravation of the disease. 3. Penicillin encephalopathy: Very few patients may develop symptoms of penicillin encephalopathy after applying penicillin in large doses, mostly seen in the elderly and young children. Patients may show abnormal mental state, and in serious cases, coma occurs. Patients are advised to use long-acting penicillin as prescribed by the doctor, and to consult the doctor promptly if there is any discomfort.