Combined Oral Contraceptive Pills (The Pill)

Combined Oral Contraceptives

Average Failure Rate: 3 - 8%

About The Pill

Commonly known as "The Pill," combined oral contraceptives are birth-control pills that include a combination of an estrogen and a progestin.

Oral contraceptive pills (The Pill or OCs) for birth control are extremely popular due to their ease of use and efficacy. Oral contraceptives come in many formulations and brands, including low dose formulations, extended use pills, and the estrogen-free mini-pill; mini-pills have fewer unwanted side-effects, but are less effective.
Popular brands of combined oral contraceptives include Yasmin, Orthocept, Ortho Tricyclen, and Ortho Novum, and Yaz.

Oral contraceptives are available by prescription only. Like all hormonal contraceptives, OCs have multiple mechanisms of action, some which prevent ovulation and others that occur after fertilization but before implantation

Estrogen and progesterone are two hormones which direct many of the processes surrounding the menstrual cycle. Artificial analogues of these have proven an efficient form of birth control. To prevent pregnancy a woman takes a pill daily which contains both of these hormones. This is the combination pill, or simply "The Pill."

Types of Combined Oral Contraceptives

Most combination oral contraceptives are packaged as "active pills" for 21 days followed by a seven day pill-free or "inactive" pill interval to allow for withdrawal bleeding (menstruation). The seven inactive pills are usually in another color. Many women prefer the 28-day packets since they do not need to remember when to start their next package of pills. At least one brand of pills contains estrogen-only pills in the fourth week.

The amount of estrogen and progestin in each pill may vary depending on when the pill is taken.

  • Monophasic OCs contain the same amount of each hormone in each active pill.
  • Biphasic OCs alter the progestin-estrogen ratio in two phases.
  • Triphasic OCs alter the progestin-estrogen ratio in three phases by varying the amounts of progestin, estrogen, or both.

Biphasic and triphasic regimens attempt to approximate a woman's natural hormonal fluctuations more closely by varying the progestin-estrogen ratios. One important goal of these formulations is to minimize the occurrence of irregular bleeding while maintaining efficacy. However, some physicians and patients prefer monophasic OCs because they are less confusing (all active pills are the same color and have the same dosage of hormones).

How Combined Oral Contraceptives Work

The estrogen works by preventing an egg from being released from the ovaries most of the time. Both the estrogen and progesterone make the uterus a hostile environment for an embryo by causing a thinning of the uterine lining. As modern combination pills contain less estrogen than their predecessors, an egg will be released by the ovaries 2-10% of the time. If fertilization takes place, the embryo will be unable to implant in the uterus, resulting in the death of the embryo.
Large doses of oral contraceptive drugs are used as a 'morning after pill' or Emergency Contraceptive Pills.

Side Effects and Health Risks of Combined Oral Contraceptives

Common side effects of oral contraceptives include:

Oral contraceptives also have some uncommon but serious health risks associated with their use, especially among smokers; these include abnormal blood clotting and heart attacks, breast cancer, and gallbladder disease.

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