I want to start taking a supplement called bullnox. will it cause my birth control to be ineffective?

Maybe (not) . . .: No definitive answer b/c there's no 3rd party oversight re dietary supplements. In other words, manufacturers aren't required to prove effectiveness or safety or truth of their miraculous claims. In fact, they don't have to prove accuracy of ingredients. So no one can address your question w/100% accuracy. Check out http://www.usatoday.com/search/dietary%20supplements/ for more info/details.