One risk of a kidney transplant is that your body will reject (fight) the new kidney. This can happen if your body’s immune system realizes that the kidney is from someone else. To prevent this from happening, you must take medicine to weaken your immune system. This medicine is called an immunosuppressant, or an anti-rejection medicine. You should take your anti-rejection medicine exactly the way your doctor tells you to. If you miss even one dose, you could risk losing your new kidney. But anti-rejection medicine also comes with risks and side effects. Talk to your doctor about what you might experience with the type of anti-rejection medicine you take.