An immunosuppressant is a type of medication that reduces the activity of the immune system. These drugs are often prescribed to prevent the body from rejecting transplanted organs, such as those from a donor, or to treat autoimmune diseases, where the immune system mistakenly attacks the body's own tissues. Immunosuppressants 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 due to a weakened immune response.