Immunosuppressants block the immune system's natural reaction to reject new, transplanted tissue.
T cells, the principal immune system cells that react against foreign tissues, are kept at bay by a carefully determined combination of immunosuppressants. The transplant recipient starts anti-rejection medication immediately after transplant, and these are maintained lifelong. To prevent rejection, transplant recipients must follow their drug regimen exactly as prescribed, taking the right dosage at the right time. A constant flow of medication in the bloodstream will help prevent rejection of the new organ. The drugs have to be strong enough to suppress the body's natural inclination to reject the transplanted organ, while causing minimal side effects to the patient.