The effectiveness of progestin-only pills is reduced by hepatic enzyme-inducing drugs such as the anticonvulsants phenytoin, carbamazepine, and barbiturates, and the antituberculosis drug rifampin.
<progestin, effect, phenytoin>, <progestin, effect, carbamazepine>, <progestin, effect, barbiturates>, <progestin, effect, rifampin>