<p>This contains two active ingredients, Gestodene and Ethinylestradiol. Ethinylestradiol is a synthetic version of oestrogen and Gestodene is a synthetic form of progesterone. If this tablet is taken according to instructions the egg cells (normally released by the ovary each month) are prevented from maturing to the point where they can be fertilized. Secondary mechanisms, which may contribute to the effectiveness of Gestop 28 as a contraceptive, include changes in the cervical mucus (which increase the difficulty of sperm penetration) and changes in the endometrium (which reduce the likelihood of implantation).</p>