Biopsy from an affected area of colon with melanosis coli showing sheets and clusters of macrophages containing the brownish-yellow pigment Lipofuscin. There is no inflammation. Melanosis coli is associated with chronic use of anthraquinone-containing laxatives such as senna and rhubarb derivatives. At endoscopy, the colorectal mucosa has dark brown-black discoloration that may be diffuse or patterened (see image 1). It is a benign reversible condition and the pigmentation disappears within months once patient stops laxative use.