Leflunomide is mainly used in the clinical treatment of rheumatoid arthritis and lupus nephritis. In practice, leflunomide has a wide range of uses and relatively few adverse reactions, and is also effective in psoriatic arthritis, scleroderma, vasculitis, and leukoarthritis. Leflunomide has relatively few side effects in clinical practice. The main side effects are white blood cell drop, skin pruritus, loss of appetite, nausea, liver damage, etc. A few patients can develop systemic symptoms, as well as colitis, constipation, black stool. Rarely, femoral necrosis, shortness of breath, dyspnea, contact dermatitis, fungal dermatitis, etc. are also seen. But overall, the side effects of leflunomide in clinical application are relatively few and the safety is relatively reliable.”