How does it work? This medicine is a combined oral contraceptive often referred to as \'The Pill\'. It contains a combination of two synthetic derivatives of naturally occuring sex hormones, oestrogen and progesterone, found in the female body. Ethinylestradiol (previously spelt ethinyloestradiol in the UK) is a synthetic version of oestrogen and levonorgestrel is a synthetic form of progesterone. During a woman\'s normal menstrual cycle, the levels of these sex hormones change. Oestrogen levels rise causing an egg to ripen (maturation) and be released from the ovaries (ovulation). This causes levels of progesterone in the body to increase, preventing the release of more eggs from the ovary and preparing the lining of the womb for a possible pregnancy. Combined oral contraceptives work by over-riding the normal menstrual cycle. Ethinylestradiol prevents the ripening and release of an egg from the ovary. Levonorgestrel works by tricking the body processes into thinking that ovulation has already occurred. In addition, levonorgestrel affects the natural mucus at the neck of the womb. It increases the thickness of this mucus making it more difficult for sperm to cross from the vagina into the womb. Levonorgestrel also acts to change the quality of the womb lining (endometrium). This prevents the successful implantation of any fertilised eggs onto the wall of the womb. When the blood levels of these hormones decrease at the end of each \'cycle\' in the packet, a menstrual period occurs. Different brands of combined oral contraceptives may contain a different type of progesterone and/or a different strength of ethinylestradiol - Low Strength (20 micrograms), Standard Strength (30 to 40 micrograms) or High Strength (50 micrograms). There may also be differences in the tablets taken during the monthly cycle. The most widely used preparations are known as \'Monophasic\'. In these, all 21 tablets are the same and a seven day pill-free gap is left between packets, during which time a period occurs. Preparations known as \'Bi- or Tri-Phasic\' have different coloured tablets which contain different strengths of oestrogen and progesterone. These tablets must be taken in the order specified on the pack for each cycle. \'ED\' (Every Day) preparations contain 28 tablets (21 active tablets and 7 inactive tablets). This allows a woman to take a tablet every day of the 28 day cycle rather than having to remember the 7 day break at the end of each pack of 21 tablets. Again, these tablets must be taken in the order specified on the pack. What is it used for? Contraception Disorders of the menstrual cycle