Immunosuppressive drugs are medications that reduce the activity of the immune system. They are commonly used to prevent the body from rejecting transplanted organs, such as kidneys or hearts, and to treat autoimmune diseases, where the immune system mistakenly attacks healthy tissues. These drugs work by inhibiting the production or function of immune cells, which can help manage conditions like rheumatoid arthritis or lupus. While they are effective in controlling these diseases, they can also increase the risk of infections and other complications due to the weakened immune response.