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: Gynaecology & Obstetrics
Drug which interferes or hampers the effectiveness of OCP are all except aEUR' 
Select and explain. 
A. Aspirin, B. Tetracycline, C. Rifampicin, D. Phenytoin
A: Aspirin
Answer: A: Aspirin 
Explanation: Aspirin