Hello dear Understand your concern Primolut -N is progesterone tablet used to post pone or prepone the period. When you withdraw the progesterone tablet, bleeding will occur as breakdown of endometrium tissue as no more progesterone to support endometrium. As you did not take the medicine for one day, result in bleeding. It does not cause any health issue. But always take primolut N under the advice of gynecologist. Also note the common side effects of primolut N:discomfort of the breasts, headaches, nausea, irregular bleeding, dizziness, weight gain and depressed mood, either sleepiness or insomnia, bloating, a decreased or increased sex drive. Hope this may help you Best regards Dr. Sagar .