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
Which of the following is an effect of grapefruit juice on drug metabolism ? 
Select and explain. 
A. Enzyme inducer, B. Enzyme inhibitor, C. Inhibits tubular secretion, D. Inhibits tubular reabsorption
B: Enzyme inhibitor
Answer: B: Enzyme inhibitor 
Explanation: Grapefruit juice contains furano cumarins and narangin that are CYP3A4 inhibitors.