The P-glycoprotein (P-gp) modulator CyA is considered one of the most effective MDR-reversing agents15, but CyA may cause a wide range of side effects, including gingival hyperplasia, peptic ulcers, hypercholesterolemia, convulsions, immunosuppression, and nephrotoxicity16. The gene discussed is ABCB1; the disease is peptic ulcer disease.