Oral contraceptives—commonly known as “the pill”—are chemicals that work by altering a woman's normal hormonal patterns so that ovulation (development and release of an egg from the ovary) does not occur. Their introduction in the late 1950s revolutionized birth control, because for the first time an effective contraceptive was available that did not have to be used in conjunction with intercourse. The pill is nearly 100 percent effective when taken according to directions, and for a number of years it was the single most popular form of birth control. More recently, however, concern has arisen about its safety, and some women are returning to methods that offer protection from sexually transmitted diseases, such as AIDS. Evidence suggests that women over the age of 35, and particularly women who smoke heavily, probably should not use the pill because of the increased risk of blood-clotting disorders, heart attack, and stroke. Studies have thus far not linked the use of the pill and the development of cancer; the chances of ovarian and uterine cancer may even be lowered with its use. Many women notice some side effects, however, such as shorter and lighter periods and, sometimes, changes in mood. Research is currently being devoted to the development of a male contraceptive pill.
The contraceptive pill, introduced in the 1960s, contains synthetic sex hormones (oestrogen and progestogen), which prevent ovulation. There has been some evidence that the contraceptive pill influences other bodily functions, in particular that it increases the risk of venous thrombosis (blood clotting), and thus carries the risk of strokes or heart attacks. To reduce this risk, a 'mini-pill' was devised, which contains progestogen but no oestrogen, and seems to have fewer associated side-effects.
Some synthetic hormone preparations work over a longer period than the contraceptive pill. Depot-Provera, for example, is a synthetic progestogen preparation injected at three-monthly intervals, while Norplant and Norplant-2 are subdermal capsules implanted under the skin of the upper arm, which last five and two years, respectively.
The current line of contraceptive research is aimed at developing a contraceptive vaccine.
The combined pill works by stopping ovulation. It thickens the mucus from the cervix. This makes it difficult for sperm to move through it and reach an egg. It makes the womb thinner so it is less likely to accept a fertilized egg.
Combined Pill
Oestrogen and progesterone inhibit production FSH. The combined pill is based on this example of negative feedback. The pill contains a mixture of these two hormones. As FSH is inhibited, no follicles are developed, ovulation cannot take place.
Synthetic forms of the hormones inhibit release of FSH and LH, preventing ovulation from taking place.
Mini-pill
Progesterone only. It is not very reliable on it’s own at inhibiting ovulation, there is still some uncertainty over the exact way it works. However, it is known to interfere with the process of cell division in the developing egg cell and can also prevent the implantation of a fertilized egg in the wall of the uterus.
Morning-after Pill
A large dose of progesterone is taken on the day after intercourse. This stimulates the lining of the uterus to develop. As it is a single dose, the concentration of progesterone in the blood decreases rapidly. This then stops implantation on the uterus lining from occurring.
Treating Infertility
Many women who are infertile have a “normal” menstrual cycle but do not ovulate. They produce a small amount of FSH but not enough to stimulate follicle production. Can be treated with a drug – clomiphine. It prevents inhibition by oestrogen so more FSH is secreted. This may be enough to trigger the normal development of a follicle, which will lead to ovulation.
