Medical Reviewing Author: Carolyn Janet Crandall, MD, FACP
Medical and Pharmacy Editor: Jay W. Marks, M.D.

GENERIC NAME: Oral Contraceptives or OCs (also known as Birth Control Pills or BCPs)

BRAND NAMES: see below

DRUG CLASS AND MECHANISM: Oral contraceptives (OCs) are medications that prevent pregnancy. They are one type of birth control. OCs may contain combinations of estrogen and progestin or progestin alone. Combinations of estrogen and progestin prevent pregnancy by inhibiting the release of the hormones LH and FSH from the pituitary gland in the brain. LH and FSH play key roles in the development of the egg and preparation of the lining of the uterus for implantation of the embryo. Progestin also makes the uterine mucus that surrounds the egg more difficult for sperm to penetrate and, therefore, for fertilization to take place. In some women, progestin inhibits ovulation (release of the egg).

The combination OCs are called "monophasic," "biphasic," or "triphasic." Monophasic OCs deliver the same amount of estrogen and progestin every day. Biphasic OCs deliver the same amount of estrogen every day for the first 21 days of the cycle. During the first half of the cycle, the progestin/estrogen ratio is lower to allow the endometrium to thicken as it normally does. During the second half of the cycle, the progestin/estrogen ratio is higher to allow normal shedding of the lining of the uterus to occur. The triphasic OCs have constant or changing estrogen concentrations and varying progestin concentrations throughout the cycle. There is no evidence that bi- or tri-phasic OCs are superior to monophasic OCs, or vice-versa.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes, for some (see below).

PREPARATIONS: Tablets, various amounts. (Please see the Birth Control article for non-oral contraceptives.)

STORAGE: All OCs should be stored between 15° (59°F) and 30°C (86°F).

PRESCRIBED FOR: OCs are prescribed for the prevention of pregnancy. When taken as directed, OCs fail in less than 1 in every 200 users over the first year of use. OCs also are prescribed to treat mid-cycle pain which some women experience with ovulation. OCs, while regulating the menstrual cycle, reduce menstrual cramps and heavy bleeding, and, because of the reduced bleeding, they may prevent the anemia that can develop in some women. Doctors sometimes prescribe higher doses of OCs for use as "morning after" pills to be taken up to 72 hours after unprotected intercourse to prevent fertilization and pregnancy.

DOSING: Many of the OCs come in easy to use dispensers in which the day of the week or a consecutive number (1, 2, 3, etc.) is written on the dispenser with a corresponding tablet for each day or number. For example, some Ortho-Novum dispensers are labeled "Sunday" next to the first tablet. Thus, the first tablet is to be taken on the first Sunday after menstruation begins (the first Sunday following the first day of a woman's period). If her period begins on Sunday, the first tablet should be taken on that day. For OCs that use consecutive numbers, the first tablet (#1) is taken on the first day of the menstrual period (the first day of bleeding). Tablet #2 is taken on the second day, and so on. Still other packages instruct women to begin on day 5 of the cycle. For such products, women count from day 1 of their menstrual cycle (day 1 is the first day of bleeding). On the fifth day, the first tablet is taken. Tablets then are taken daily.

OCs are packaged as 21-day or 28-day units. For 21-day packages, tablets are taken daily for 21 days. This is followed by a 7-day period during which no OCs are taken. Then the cycle repeats. For the 28-day units, tablets containing medication are taken for 21 consecutive days, followed by a seven-day period during which placebo tablets (containing no medication) are taken.

Women just starting to take OCs should use additional contraception for the first 7 days of use because pregnancy may occur during this period of time.

If women forget to take tablets, pregnancy may result. If a single tablet is forgotten, it should be taken as soon as it is realized that it is forgotten. If more than one tablet is forgotten, the instructions that come with the packaging should be consulted, or a physician or pharmacist should be called.

DRUG INTERACTIONS: Estrogens can inhibit the metabolism (elimination) of cyclosporine, resulting in increased cyclosporine blood levels. Such increased blood levels can result in kidney and/or liver damage. If this combination cannot be avoided, cyclosporine concentrations can be monitored, and the dose of cyclosporine can be adjusted to assure that its blood levels do not become elevated.

Estrogens appear to increase the risk of liver disease in patients receiving dantrolene through an unknown mechanism. Women over 35 years of age and those with a history of liver disease are especially at risk.

Estrogens increase the liver's ability to manufacture clotting factors. Because of this, patients receiving warfarin (Coumadin) need to be monitored for loss of anticoagulant (blood thinning) effect if an estrogen is begun.

A number of medications, including some antibiotics, can decrease the blood levels of OC hormones that would otherwise have been achieved during OC use, but an actual decrease in the effectiveness of the OC has not been convincingly proven. Nonetheless, because of this theoretical possibility, some physicians recommend back-up contraceptive methods during antibiotic use. Carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin), primidone (Mysoline), rifampin (Rifadin), rifabutin (Mycobutin), and ritonavir (Norvir) each increase the elimination of estrogens. OCs with higher concentrations of estrogen or alternative forms of contraception may be necessary in women using those medications.

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