Girlfriend is on the cerrelle birth control pill. is it normal for this pill to prevent her from getting her period? please help doc. thank you.

Possible: Cerelle is a what is called a progesterone only pill and does not contain like many birth control pills estrogen. The downside to the absence of estrogen is that women on Cerelle may experience irregular breakthrough spotting/bleeding, or, like your girl friend, no menses at all. Progesterone only pills are very effective, so pregnancy is unlikely - unless she missed taking pills.