Sirolimus is a medication primarily used to prevent organ rejection in patients who have received a kidney transplant. It works by inhibiting a specific protein that plays a crucial role in cell growth and division, thereby suppressing the immune response. This helps the body accept the new organ without attacking it. In addition to its use in transplants, Sirolimus has also been studied for treating certain types of cancer and rare diseases. It is often prescribed in combination with other immunosuppressive drugs to enhance its effectiveness while minimizing potential side effects.