This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Melanosis coli is caused by 
Select and explain. 
A. Bisacodyl, B. Senna, C. Magnesium sulphate, D. Lactulose
B: Senna
Answer: B: Senna 
Explanation: Senna and cascara are anthraquinone derivatives, which are used as stimulant purgatives. On chronic use they can lead to melanosis coli.