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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Birth-Control Pills 101

September 30, 2013

By Harold J. DeMonaco M.S.

Harvard Medical School

An Overview of Oral Contraceptives

Oral contraceptives have gone through many changes through the years since they were introduced in the 1960s. The early forms of oral contraceptives (also known as birth control pills) had a good deal of estrogen in them than when they first became available. Today's birth control pills have a lot less hormone in them. That's because we have learned that they are still effective at much lower doses, which are safer. Birth control pills usually contain a combination of an estrogen and a progestogen (these are called combined birth control pills). Some only have a progestogen and are called "minipills."

Combined birth control pills work by preventing ovulation (the release of a mature egg from a woman's ovary). The estrogen in the pill causes this. Without the release of the egg, pregnancy can't happen. Combined birth control pills also work by making cervical secretions thicker, making it very difficult for sperm to get into the uterus; by causing changes in the fallopian tubes (the tubes that carry the egg from the ovaries to the uterus); and by making it hard for a fertilized egg to implant. These effects are caused by the progestogen in combination birth control pills. The minipills do not usually prevent ovulation because they don't contain estrogen. The minipills are good for women who either have difficulty taking estrogen or who are at some risk in taking estrogen (for example, women who smoke).

When taken regularly and according to the directions, birth control pills are 98% to 99% effective in preventing pregnancy, depending on how much estrogen they contain. The more estrogen, the better the birth control effect. Unfortunately, the more estrogen, the higher the likelihood of side effects.

Minipills do not contain any estrogen and are about 98% effective. But they need to be taken exactly as directed. Even missing one pill can greatly reduce effectiveness. Therefore, many physicians suggest another method of birth control such as a condom or diaphragm be used in addition to the minipill, especially for sexual activity in mid-cycle.

The most common reason for pregnancy in a woman taking birth control pills is a failure to take them as directed. You should be familiar with the instructions that come with the dispenser for what to do if you miss a dose. It is a good idea to use a second method such as a condom or diaphragm for the rest of the month, even if you miss only one dose.

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The Different Kinds of Pills

Birth control pills not only come in combination and as a minipill. The combination pills are also available in three different forms: monophasic, biphasic and triphasic.

Monophasic birth control pills — In these, all of the doses of estrogen and progestogen are exactly the same for 21 days of the 28-day cycle. The last seven days are filler doses — pills containing no active drug that are included to allow you to keep to a daily schedule.

Oral contraceptives packages usually contain 21 days of active tablets along with seven days' worth of inert sugar pills. The oral contraceptive is taken for three weeks of the cycle, followed by seven days of sugar pills. This maintains a 28-day cycle. Some pills, however, use a cycle with 24 days of hormone and a four-day pill-free interval to help decrease side effects and improve effectiveness. It's not clear though that they are superior to the standard pills. Women usually have their period within a couple of days of starting the sugar pills.

If a woman continued to take the active pills and not use the sugar pills, she presumably would not menstruate. Many gynecologists have been advising women for years about this. Women use this technique to "skip" a period. It is important to note that this can be done only with monophasic birth control pills. Many gynecologists recommend that the "skipping" be done for no more than three to four months in a row.

The U.S. Food and Drug Administration (FDA) approved packaging of a monophasic birth-control pill called Seasonale in 2003. The product is packaged in a 91-day supply and is designed to prevent menstruation for the entire time period. Women taking Seasonale will have only four periods a year. Seasonale contains the same estrogen (ethinyl estradiol) and progestin (levonorgestrel) in the same amount as many other monophasic birth control pills. Although many other monophasic birth control pills are used in this way, Seasonale is the only product approved for use. As you would expect, Seasonale is priced higher than the equivalent three one-month supplies of the generic products containing the same ingredients in the same amount.

Examples of monophasics include Apri, Brevicon, Desogen, Loestrin, Lo/Ovral, Modicon, Necon, Nordette, Norinyl, Ortho-Cyclen, Ortho-Novum, Ovcon, Ovral, Portia, Sprintec, and Zovia.

Biphasic birth control pills — These have a fixed amount of estrogen, but there are two different strengths of progestogen in the dispenser. The first seven to 10 days are one strength (and one color). The next 11 to 14 tablets are another strength (and another color). Finally, the last seven days are filler doses containing no active drug.

Examples include Mircette, Necon 10/11, and Ortho-Novum 10/11.

Triphasic birth control pills — Depending on the brand, the amount of estrogen may change as well as the amount of progestogen. There are actually three different strengths in the dispenser. The first five, six, seven or 10 days are one strength (and one color). The next five, seven or nine tablets are another strength (and another color). The next five, seven, nine or 10 tablets are the third and final phase. The last seven days are filler doses containing no active drug.

Examples include Estrostep-28, Ortho-Novum 7/7/7, Ortho Tri-Cyclen, Tri-Sprintec, Tri-Norinyl, Triphasil and Trivora.

Progestogen-only birth control pills (the minipill) — These are not combination products and do not contain any estrogen. Each tablet in the minipills is the same. There are no filler pills, so a hormone tablet must be taken every day. The pill must be taken within the same three-hour window to be most effective. It is important to know that because there is no estrogen, the risk of pregnancy is somewhat higher with these products than with birth control pills that do contain estrogen.

Examples include Micronor, Nor-QD and Camila.

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Using the Pill as Emergency Contraception

Two types of oral-contraceptive products are used as an emergency contraceptive.  Plan B contains the progestogen levonorgestrel.  It should be taken as soon as possible after unprotected intercourse because its effectiveness decreases after 72 hours.  It can be taken as a single 1.5 mg dose (Plan B One-Step) or as two doses of 0.75 mg taken 12 hours apart.  The single dose is preferred because of its convenience. Generic forms of Plan B are also available (Next Choice, for example). These forms of levonorgestrel for emergency contraception are now available over the counter without a prescription.

Combined estrogen-progesterone oral contraceptives can also be used for emergency contraception but currently none are specifically packaged for this use. The treatment requires a specific number of oral contraceptive pills taken as soon as possible after unprotected sex, and then a second dose 12 hours later. Some examples are listed below.

Emergency Use of Oral Contraceptives
Oral Contraceptive Pills per dose
Plan B* 1 white
Ovral 2 white
Alesse 5 pink
Levlite 5 pink
Nordette 4 light orange
Levora 4 white
Lo/Ovral 4 white
Low-Ogestrel 4 white
Triphasil 4 yellow
Trivora 4 pink
Ovrette 20 yellow

*Plan B is packaged for emergency contraception and is FDA approved for this use.

A newer drug for emergency contraception is Ulipristal (brand name Ella).  It is not a hormone contraceptive but rather an anti-progestagen. It is available only with a prescription.

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Deciding Which Pill Is Right for You

Some important points to consider when choosing a birth control pill:

    • Despite all of the advertising, monophasic birth control pills work as well as the more expensive and more complicated biphasic and triphasic products. All combination products containing both estrogen and progestogen are more effective in preventing pregnancy than are the "minipills." So for most women, the monophasic birth control pills represent a good first option. Prices for the products vary widely, however, ranging from about $20 a month to $50. Your insurance coverage will determine your cost. There is no evidence that brand name pills are better than generic pills.
    • Monophasic products with low amounts of estrogen may cause less bloating or breast tenderness but more breakthrough bleeding.
    • There is little evidence to suggest that any birth control pills that contain both estrogen and progestogen are any better for treating acne than any others. All appear to work.
    • Birth control pills need to be taken as directed. You should know what to do if you miss a dose. The instructions that come with the dispenser will tell you what you should know.

No single birth control pill is right for every woman, so it may take some trial and error to find the right one for you. The secret is trying to get the right hormonal balance — just enough to prevent pregnancy, but not enough to cause side effects. It may take two or three cycles to adjust to the medication. So don't give up on a particular pill too quickly.

If you are having trouble with a product, here are some hints:

You are probably getting too much estrogen if you are experiencing:

  • Nausea
  • Bloating
  • High blood pressure
  • Headache
  • Breast fullness or tenderness
  • Swelling of the ankles

You are probably not getting enough estrogen if you are experiencing:

  • Early or mid-cycle bleeding
  • Spotting

You are probably getting too much progestogen if you are experiencing:

  • Increased appetite or weight gain
  • Tiredness
  • Acne
  • Hair loss
  • Depression
  • Vaginal yeast infections

You are probably not getting enough progestogen if you are experiencing:

  • Late breakthrough bleeding
  • No period at all

You and your doctor have lots of options from which to choose. Despite what the advertising says, there is no single best birth control pill. Whatever works for you is the best option.

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Harold J. DeMonaco, M.S., is senior clinical associate in the Decision Support and Quality Management Unit at the Massachusetts General Hospital and is currently a Visiting Scholar at the MIT Sloan School of Management. He is author of over 20 publications in the pharmacy and medical literature and routinely reviews manuscript submissions for eight medical journals.

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