Immunosuppressants are drugs that have a suppressive effect on the immune response of the body. Since many rheumatic diseases are caused by hyperactive immune function of the body, immunosuppressants can control the development process of many rheumatic diseases and thus play a therapeutic role. The commonly used immunosuppressive agents are alkylating agents such as cyclophosphamide and antimetabolites, methotrexate and azathioprine. Immunosuppressants are often used in more severe or rapidly progressing rheumatic diseases and in rheumatic diseases where NSAIDs or hormone therapy is not effective. However, they are often not used as routine first-line drugs because of the significant toxic side effects. The main side effects of cyclophosphamide are bone marrow suppression, causing leukopenia, erythrocyte reduction, anemia, and also serious gastrointestinal reactions such as nausea and vomiting. As its metabolites are excreted from the urine and irritate the urethra, it can lead to hemorrhagic cystitis, urinary urgency, frequency and hematuria, and in severe cases, cancer. It can also cause decreased fertility. It is not necessary to stop treatment for temporary hair loss caused by cyclophosphamide. Methotrexate and azathioprine also have the aforementioned side effects and must be applied rationally under the guidance of a physician.