Why is it necessary for doctors to give organ transplant patient a drug called cyclosporine?

After undergoing an organ transplant, it is necessary for patients to take drugs called immunosuppressants for the rest of their lives. Cyclosporine is a commonly used drug for this purpose. It is extremely important that people who have had a transplant take this drug every day as directed because if they don't, their body may reject the organ. The body's immune system recognizes the new organ as foreign and it attacks it. Drugs such as cyclosporine will suppress the immune system so that it cannot destroy the organ.