<prompt> A 20 years old nulliparous woman is an oral contraceptives pills. She is currently diagnosed as having pulmonary tuberculosis which antituberculous drug decreases the effect of OCP.INHPyrazinamideEthambutolRifampicin  <response>: Ans. is d i.e.,. Rifampicin Ref KDT in, 1101, p. 754.There is not much to explain in this one as you know refampicin is a microsomal enzyme inducer which enhances its own metabolism as well as that of many drugs like - WarfarinOCP in DigitoxinSulfonylureasSteroids 