A drug used to treat skin conditions that increase the skin’s sensitivity to sunlight. Methoxsalen (8-MOP, Oxsoralen) is a very strong medicine used along with ultraviolet light to treat vitiligo, a condition in which skin color is lost, and psoriasis, a skin disorder associated with red, scaly patches. It is also used with ultraviolet light to treat skin problems associated with a type of cancer called mycosis fungoides. Methoxsalen is capable of causing severe sunburn, premature aging of the skin, skin cancer, and cataracts. It should be used only as prescribed.