Tacrolimus is primarily used as an immunosuppressive drug to prevent organ rejection in patients who have undergone organ transplants, such as kidney, liver, or heart transplants. It works by inhibiting the activity of T-cells, which play a key role in the immune response, thereby reducing the risk of the body attacking the transplanted organ.

In addition to its use in transplant medicine, tacrolimus is also applied topically to treat moderate to severe atopic dermatitis (eczema) in patients who do not respond well to other treatments. The topical form helps to reduce inflammation and soothe the skin by suppressing the immune response in the affected area.

Tacrolimus is also being investigated for its potential use in treating other autoimmune conditions, such as psoriasis, lupus, and certain types of uveitis, due to its ability to modulate the immune system. However, its use in these areas is still under research and not yet widely established.

Due to its potent immunosuppressive effects, tacrolimus requires careful monitoring to manage potential side effects, such as increased risk of infections, kidney dysfunction, or high blood pressure.