Tacrolimus capsules are calmodulin inhibitors, which belong to the class of immunosuppressive drugs used for anti-rejection reactions after organ transplantation. Studies have found outstanding efficacy in immunosuppression with relatively few side effects, so it is now widely used in rheumatoid and nephrotic syndromes, and tacrolimus is also used in autoimmune diseases, most commonly in organ transplant patients. Tacrolimus is a milestone drug in the history of organ transplantation and drug development after cyclosporine, and its birth has brought great benefits to the majority of patients. Tacrolimus, as an immunosuppressant, has obvious efficacy but also very clear adverse effects, so this type of drug should be used in the right dosage and with the right course of treatment for the disease under the clear diagnosis of the physician and supervision of the pharmacist.