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
OCP failure by rifampicin is due to - 
Select and explain. 
A. Decreased absorption of OCP, B. Increased binding of OCPs by rifampicin and reduced free drug concentration, C. Increased metabolism of drug, D. Increased chances of ovulation due to rifampicin
C: Increased metabolism of drug
Answer: C: Increased metabolism of drug 
Explanation: Ans. is 'c' i.e., Increased metabolism of drug