Immunosuppressants are drugs or medicines that lower the body\'s ability to reject a transplanted organ. Immunosuppressants agents inhibit cell mediated immune response by various mechanisms. Immunosuppressants include azathioprine, cyclosporine, methotrexate, mycophenolic acid, sirolimus, and tacrolimus. Action, uses, dosages and side effects of all these drugs are also covered in this chapter. Common side effects are anorexia, nausea, vomiting, hepatotoxicity, anemia, leukopenia, thrombocytopenia, chills, fever, and alopecia. Serious one is serum sickness.