The Pill contains one or more hormones which interfere with the normal pattern of hormone production in females. Taken over 21 or 28 days of a typical monthly cycle, they suppress ovulation. Additionally, the Pill makes the mucus in the cervix very thick, so that sperm have trouble passing into the uterus. The lining of the uterus is also thinned, making it difficult for a fertilized egg to implant. Women still have menstrual periods while on the Pill, because the levels of hormone in some of the pills varies, so that the uterus does build up a small lining and then sheds it at the end of the cycle.
Pills have to be taken very regularly.
If a women misses even 2 or 3 days of pills during the month, she must use another form of contraception until the next cycle, because her own body might override the pill and produce an egg. A woman needs a doctor's presription to take the Pill. Injectable Progestin is a synthetic hormone that is given as a shot into the muscle every three months. It works the same way as the Pill. The main type of this contraceptive used in the United States is called Depo-Provera.