The body recognizes that the new organ transplanted is not of its own and try to attack and damage the transplanted organ and this process is known as rejection. The basic purpose of the immunosuppressive drugs is to prevent the process of rejection by weakening the response of your immune system. Thus on one side less dose of immunosuppressive drugs would made the transplanted organ more susceptible to rejection where as on the other hand more dose of these drugs would make you prone to develop various kinds of infection as well develop toxic side effect of these drugs. Fortunately the amount of immunosuppressive drugs necessary to maintain the organ healthy decreases with time but you would have to continue some of these drugs indefinitely. The treating transplant physician would perform various tests to find out the correct doses of immunosuppressive drug so that the chances of developing rejection or infection are minimized. Never try to skip or reduce the dose without informing the doctor as they may have serious consequences.