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 effectiveness of OCP are all, EXCEPT: 
Select and explain. 
A. Aspirin, B. Phenobarbital, C. Rifampicin, D. Primidone
A: Aspirin
Answer: A: Aspirin 
Explanation: Contraceptive failure may occur if the following drugs are used concurrently: Enzyme inducers like Phenytoin, Phenobarbital, primidone, carbamazepine, rifampin. It will increase the metabolism of estrogenic as well as progestational component. Suppression of intestinal microflora: Tetracyclines and ampicillin etc. No deconjugation of estrogens excreted in bile-their enterohepatic circulation is interrupted-blood levels fall. Also Know: Absolute Contraindication of OCP: Thromboembolic, coronary and cerebrovascular disease or history of it Moderate to severe hypeension Hyperlipidemia Active liver disease Hepatoma H/o of jaundice during past pregnancy Malignancy of Breast/genitalis Porphyria Impending major surgery- to avoid postoperative thromboembolism. Ref: K.D.T. 6th Ed Page 317