Used primarily as an immunosuppressive agent in organ transplantation to prevent rejection by inhibiting T-cell activation. Widely applied in kidney, liver, and heart transplants. Also used in treatment of autoimmune diseases such as severe psoriasis, rheumatoid arthritis, and atopic dermatitis due to its ability to modulate immune response. Available in oral and intravenous formulations for systemic use, and in ophthalmic preparations for dry eye disease. Its targeted action on calcineurin makes it effective with relatively fewer broad immunosuppressive effects compared to other agents.