Hello, Thanks for posting in HCM. Usually with medications like antibiotics or antihypertensive or antidiabetics this phenomenon is seen as body becomes used to the dosages and thus it becomes ineffective after certain period of time. But BC pills are only hormones and even in body the same phenomenon goes on from menarche to menopause. Taking hormonal pills just are additives to the hormonal levels to keep cycles regular plus anti pregnancy effect. So it will not become ineffective even if taken for long time. But there are other side effects of these pills on body such as obesity, probability of DVT or thrombus formations. Also after very long time, effects on hearts are also noted. So use it cautiously and keep following up with your doctor so as to pick up any ill effects of these tablets early. I hope I answered your question satisfactorily. If you have any more query kindly write back to me, will be happy to help you out. Thank you.