Young women smoking, does it reduce the effectiveness of birth control?

Yes: Smoking increases the metabolism of many drugs, including some of the ones used in oral contraceptives. Even more importantly, smoking increases the potential serious side effects of these drugs, especially blood clotting potential. Women who smoke and use ocps are at high risk of deep venous thrombosis (blood clots in legs) and these traveling to lung-pulmonary embolism, which can be fatal.