The immune system is essential for fighting infection and disease. But, if your immune system is too active it can harm the body rather than protect it. Immuno-suppressant medicines lower the activity of your immune system. Medicines such as ciclosporin and mycophenolate can be used after organ transplantation to prevent rejection of the organ. Disease-modifying anti-rheumatic drugs (DMARDs) such as leflunomide and penicillamine are used to manage rheumatoid arthritis, an auto-immune disease that causes pain and restricted movement.