The oral contraceptive, commonly called the pill, stops the ovaries from releas- ing eggs (ovulation) and blocks sperm from reaching an egg, or it prevents a fer- tilized egg from attaching to the wall of the uterus. Oral contraceptive pills contain either a combination of progestin (a synthetic form of the female hor- mone progesterone) and estrogen (the key female sex hormone) or progestin alone. The combination pills are taken daily for 3 weeks, stopped for a week to allow for the menstrual period, and then started again. They prevent the ripening and release of the egg.
A variation of the combination pill is the multiphasic pill. This newer version varies the amount of estrogen and progesterone throughout the menstrual cycle to more closely match the hormone changes that occur naturally. Simply put, the pill’s hormones trick the body into thinking it is pregnant. After ovulation, ele- vated levels of estrogen and progesterone prevent the release of another egg during the menstrual cycle. The pill provides these hormones on a daily basis, suspending ovulation.
Progestin-only pills, also called minipills, are taken every day of the month, but they do not suspend ovulation. They work by making the mucus that lines the cervix (the opening into the uterus from the vagina) so thick that sperm cannot pass through it and reach the egg. Bleeding usually occurs during the last few days of the menstrual cycle.
When used properly, combination pills are as effective as the progestin-only pill and are more effective for long-term use. The progestin-only pill is usually prescribed only when estrogen might be harmful to the woman, such as when she is breast-feeding.
The pill can sometimes cause problems, such as ﬂuid retention, weight gain, irritability, and a change in sex drive. Women over 35 who smoke and women with active liver disease such as hepatitis B, or who have advanced diabetes are advised not to take the pill as a precaution against possible complications.
Increasing evidence indicates that the pill provides health beneﬁts in addition to preventing pregnancy. For example, the pill has beneﬁcial effects on benign breast tumors and ovarian cysts, and signiﬁcantly reduces the risk of ovarian and endometrial cancers, iron-deﬁciency anemia, pelvic inﬂammatory disease, and ectopic pregnancy. The longer a woman takes the pill, the greater the protective effects.
The so-called morning-after pill is a series of birth-control pills containing the female sex hormones estrogen and progestin. The ﬁrst dose must be taken within 72 hours of the unprotected sexual intercourse. This inhibits growth of the lining of the uterus so it cannot sustain a fertilized egg. Morning-after pills are highly effective in preventing pregnancy when used correctly. Possible side effects include nausea, breast tenderness, and spotting (light vaginal bleeding).