Dear Madam, Hi & Welcome. Because Primolut-N is not found to be safe during pregnancy. Primolut-N (Norethisterone) which is mainly used to regularize abnormal menstrual bleeding, lack of monthly menstrual bleeding, delayed periods in certain conditions like polycystic disease of the ovaries, to postpone the period, etc. These tablets will not provide contraceptive cover. Hence there is chance of pregnancy following an unprotected sex. It is better to use condoms along with these tablets for protection. You can take oral contraceptive (birth control) pills along with Primolut N after consulting your doctor. It may cause fetal deformities if taken inadvertently during pregnancy or suspected pregnancy. It may also cause virilization of female unborn babies especially after 45 days of pregnancy. It should be stopped once the pregnancy is confirmed by the ultrasound. Hope these answer your query.