A group of oral drug preparations containing one or more synthetic female sex hormones, taken by women in a monthly cycle to prevent pregnancy. “The pill” commonly refers to the combined or the phased pill, which both contain an oestrogen drug and a progestogen drug, and the minipill, which contains only a progestogen. Oestrogen pills include ethinylestradiol; progestogens include levonorgestrel and norethisterone. When used correctly, the number of pregnancies among women using oral contraceptives for one year is less than 1 per cent. Actual failure rates may be 4 times higher, particularly for the minipill, which has to be taken at precisely the same time each day.
Combined and phased pills increase oestrogen and progesterone levels. This interferes with the production of two hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn prevents ovulation. The minipill works mainly by making the mucus lining of the cervix too thick to be penetrated by sperm.
Oestrogen-containing pills offer protection against uterine and ovarian cancer, ovarian cysts, endometriosis, and irondeficiency anaemia. They also tend to make menstrual periods regular, lighter, and relatively pain-free. Possible side effects include nausea, weight gain, depression, swollen breasts, reduced sex drive, increased appetite, leg and abdominal cramps, headaches, and dizziness. More seriously, there is a risk of thrombosis causing a stroke or a pulmonary embolism. These pills may also aggravate heart disease or cause hypertension, gallstones, jaundice, and, very rarely, liver cancer. All oral contraceptives can cause bleeding between periods, especially the minipill. Other possible adverse effects of the minipill include irregular periods, ectopic pregnancy, and ovarian cysts. There may be a slightly increased long-term risk of breast cancer for women taking the combined pill.
Oestrogen-based pills should generally be avoided in women with hypertension, hyperlipidaemia, liver disease, migraine, otosclerosis, or who are at increased risk of a thrombosis. They are not usually prescribed to a woman with a personal or family history of heart or circulatory disorders, or who suffers from unexplained vaginal bleeding. The minipill or a lowoestrogen pill may be used by women who should avoid oestrogens. Combined or phased pills may interfere with milk production and should not be taken during breast-feeding. Certain drugs may impair the effectiveness of oral contraceptives. (See also contraception.) ... oral contraceptives
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