Leukopenia mainly has the following three causes: 1) Drugs; 2) Infections; 3) Diseases that cause disturbances in white blood cell production. Drugs primarily include antibiotics such as sulfonamide antibiotics and penicillin; anti-tuberculosis drugs like rifampicin and isoniazid; anti-thyroid drugs such as methimazole and propylthiouracil; antipyretic analgesics like aminopyrine, indomethacin, and ibuprofen; and antihistamines such as diphenhydramine. Additionally, most chemotherapy drugs can cause a decrease in white blood cells. Viral infections can lead to a decrease in white blood cells or severe bacterial infections, such as sepsis and septicemia, along with some chronic infections. Diseases that cause disturbances in the production of white blood cells mainly refer to certain hematological diseases, such as aplastic anemia or malignant tumors that invade the bone marrow and affect hematopoiesis. Furthermore, there are some less common causes of leukopenia, such as familial inheritance and granulocyte distribution disorders.