I asked befor but didn't get proper answer. does smoking decreas efecctivness of pill? yes i know about risk of cigares combine with pills.

You mean BCP's: or birth control pills (or oral contraceptives) which are combinations usually of an estrogen and a Progesterone product, often both synthetic or semi-synthetic. Smoking does not specifically effect the effectiveness of the pill per se, but there are vastly greater risk to the woman who smokes and uses OCPs of getting blood clots - in the lower legs which can travel to the lungs and be fatal.