Immunosuppression means to lower the activity of the immune system. This can be done in case the immune system is likely to complicate a medical treatment such as an organ transplantation. Some diseases make the immune system attack healthy parts of the body, for example Lupus, Rheumatoid arthritis or Multiple sclerosis. By decreasing the effectiveness of the immune system, the damage caused by the illness can be reduced. The most common drug used for this purpose is Cortisol.