FK506 (tacrolimus), a calcineurin inhibitor, is widely used as an immunosuppressant to lower the risk of organ rejection after organ transplantation, and to treat T cell-mediated diseases such as eczema and atopic dermatitis. FK506 treatment often accompanies pain sensation in patients with atopic dermatitis or after organ transplantation. In previous studies, the investigators confirmed that FK506 treatment increased neuronal activity of primary afferent neurons and causes pain behavior in naïve mice. In order to further search for objective clinical evidence, the investigators proposed to investigate pain incidence after FK506 immunosuppressive therapy in liver transplantation patients. The investigators will investigate pain incidence and pain intensity in patients who underwent liver transplant from September of 2011 to May of 2018 in the Liver Health Rehabilitation Association. The patients who were divided into two groups based on whether or not FK506 was used in the immunosuppressive therapy. The patients in control group (without FK506 treatment) and FK506-treated group report pain sensation 3 months and 12 months after liver transplant. The investigators will compare the pain incidence between the two groups at both time points. On the other hand, the investigators will further investigate changes in pain sensation after 1st and 2nd reductions of FK506 dose. Pain is reported subjectively by the patient using the visual analogue scale (VAS) 1 month after dose reduction. In our study, 1st and 2nd reductions of FK506 dose refers to the first two dose-adjustments (approximately 6 months apart) that occurred 3-6 months after the liver transplantation.