Methoxsalen belongs to the group of medicines called psoralens. It is used along with ultraviolet light (found in sunlight and some special lamps) to treat the white blood cells from your blood in a process called photopheresis. The treated white blood cells are returned to your body to control skin problems associated with cutaneous T-cell lymphoma, a cancer of the lymph system. Methoxsalen is to be administered only by or under the supervision of your doctor or other health care professional.