Immunosuppressant drugs are medicines that reduce the body's natural defenses against foreign invaders or materials. Used in transplant patients, these drugs help prevent their bodies from rejecting transplanted organs.

When an organ, such as a liver, a heart or a kidney, is transplanted from one person (the donor) into another (the recipient), the recipient's immune system has the same response it has to any foreign material: It attacks and tries to destroy the organ. Immunosuppressant drugs help prevent this from happening by subduing the natural immune response. However, the drugs' action also makes the body more vulnerable to infection. For that reason, people who take these kinds of medicine need to be especially careful to avoid infections.

In addition to being used to prevent organ rejection, immunosuppressant drugs sometimes are used to treat severe skin disorders such as psoriasis and other diseases such as rheumatoid arthritis...