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There are several types of drugs that alter hormonal levels in women; these drugs suppress the hormonal signal sent by the pituitary gland for the ovaries to release an egg. One such drug is a birth-control pill—a combination of synthetic estrogen and synthetic progesterone—which inhibits ovulation by simulating the biochemical action by which ovulation is arrested during pregnancy.
Another drug, the "mini-pill," contains synthetic progesterone, which inhibits ovulation only half the time, but also prevents the necessary monthly enrichment of the uterine lining and hampers sperm motility.
Generally, birth-control pills must be taken orally on a precise schedule for 21 days (or 28, if the pack provides a week of placebos) during each menstrual cycle, the exact number of days depending on the contents of the pill. Birth-control drugs need not be administered orally.
Depo-Provera, a progesterone available in many countries, is administered by injection once every three months. Norplant consists of a set of small, soft tubes that are surgically implanted under the skin of a woman's arm, where they release the synthetic hormone progestin. Norplant can prevent conception for up to five years.
The "morning-after pill"—a series of pills containing either high dosages of both estrogen and progestogen (any progestational steroid, such as progesterone) or only progestogen—is one of the few methods for preventing pregnancy after intercourse.
The safety of the use of hormonal contraceptives remains controversial. In addition to such troublesome but nonthreatening side effects as weight gain and nausea, the use of oral contraceptives has been linked to a greater incidence of blood-clotting disorders. High-risk groups include women over the age of 35, women who smoke, and women who have a history of clotting disorders, diabetes, high blood pressure, sickle-cell anemia, or various other conditions.
Decreasing the hormonal dosage has mitigated some side effects, and further research has demonstrated some benefits, such as the prevention of certain kinds of tumour growth. Possible links between hormonal contraceptives and cancer or infertility have been the object of study.
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