Anti-rejection medications, suppress your body’s natural defence system (immune system) to prevent it from recognizing your transplant as a “foreign invader” and attacking it. The result of such an attack is rejection. By taking these medications your immune system is lowered enough for you to safely keep your organ. It is essential that you take anti-rejection medications at the same time every day and 12 hours apart to avoid missing doses and to keep consistent blood levels of the medication in your body. Make sure that you understand the directions. Never change your dose unless your physician tells you to do so.