Contraceptive Pill: How Does it Work, How Effective are they, When to Start Taking it, Side-Effects and Benefits

contraceptive pill effectiveness

There are some types of contraceptive pills, which consist of synthetic versions of the hormones estrogen and progesterone is the most commonly used.

Since their introduction in the 1960’s, millions of women have used oral contraceptive pills. Oral contraceptives (birth control pills) are used to prevent pregnancy.

Estrogen and progestin are two female sex hormones. The combination of estrogen and progestin helps to avoid ovulation, which is the release of ovarian eggs.

She also modified the lining of the uterus to prevent the development of pregnancy and alter the lining of the cervix (inhibition of the womb) to prevent sperm (male reproductive cells) from entering.

Oral contraceptives are a useful contraceptive method, but they do not prevent the spread of the Human Immunodeficiency Virus (HIV); The virus that causes Acquired Immunodeficiency Syndrome (AIDS) and other sexually transmitted diseases.

Birth control pills are a type of medication that women can take daily to prevent pregnancy. They are also called the “pill” or oral contraception.

The combined contraceptive pill prevents pregnancy by stopping the release of eggs by the ovaries (preventing ovulation).

This capsule also increases the mucus in the neck of the womb, so that it’s more difficult for sperm to reach the uterus. Thinning of the womb lining also occurs, so any fertilized egg is less likely to implant successfully.

Other forms of contraceptive pill include the progestin-only (progesterone-only) pill, which can be used by women who can’t use the combined pill for medical reasons.

The emergency contraceptive pill (“morning after” pill) is a common form of emergency contraception.

How does it work?

Most contraceptive pills are “combination pills” that contain a combination of estrogen and progesterone to prevent ovulation (the release of an egg during the menstrual cycle). If they do not ovulate, women can not get pregnant because there is no egg to fertilize.

Another effect of the pill is the thickening of the mucus that surrounds the cervix, which makes it difficult for the sperm to enter the uterus and reach an egg that the ovary releases.

In some cases, the hormones in the pill can also affect the lining of the uterus, making it difficult for the ovum to attach to its walls.

Most combination pills come in presentations for 21 days or 28 days. A capsule with hormones is taken every day at about the same time for 21 days.

Depending on the version you chose, you can stop taking the contraceptive pill for seven days (in the presentation for 21 days), or you can take a pill without hormones for seven days.

Women menstruate when they stop taking the pills with hormones. Some women prefer the 28-days version because it helps them get used to taking medicine every day.

There is also a type of combination pill that reduces the frequency of menstruation; a hormone pill should be taken for 12 weeks and then a placebo for seven days.

This medicine reduces the period of menstruation to once every three months, instead of once a month.

Another type of pill that can alter the frequency of menstruation is the pill with low doses of progesterone, also called minipill.

This type of contraceptive pill differs from the rest because it has only one kind of hormone (progesterone) instead of a combination of estrogen and progesterone.

It works by altering the mucus from the lining and cervix and, in some cases, also affects ovulation. The mini-pill may be a little less effective at preventing pregnancy than the combined pills.

The minipill is taken every day without interruption. Women who take the minipill may not menstruate or have an irregular menstrual period.

For it to work, people should take the minipill at the same time every day, without omitting any dose.

All birth control medicines are more effective if people take them every day at the same time; whether you plan to have sex or not. This especially applies to pills that only contain progesterone.

When you start taking the pill, for the first seven days, women should use an additional form of birth control, such as condoms, to prevent pregnancy.

After seven days, the pill can be used alone to prevent pregnancy. You can continue to use condoms to prevent sexually transmitted diseases (STDs).

If women stop taking the pills or merely forget to, the contraceptive method will not work, and they should look for an alternative, such as condoms. Another option is to stop having sex for a while. Do not take pills from a friend or relative.

Combined Contraceptive Pill

The basic form of this pill is the monophasic pill. You typically take pills for 21 days, then have seven days off. Some people make use of seven dummy pills for the seven days without the medication.

These sometimes contain iron supplements. During this time, withdrawal bleeding occurs, in a similar manner to a regular period.

An example of a monophasic pill is “Alesse,” which contains Levonorgestrel (a progestin, or synthetic analog of progesterone) and Eethinyl Estradiol (a synthetic analog of estrogen). Alesse gives you 21 active pills and seven dummy pills.

“Seasonale” also contains Levonorgestrel and Eethinyl Estradiol, but gives you 84 active pills and seven dummy pills, so you have periods every 12 weeks.

“Yasmin” and “Yaz” are pills which contain drospirenone (a progestin, or synthetic analog of progesterone) and Eethinyl Estradiol.

Biphasic pills change the relative levels of the progestin and estrogen compounds once during the active cycle. “Ortho-novum 10/11,” which contains the progestin norethindrone and the estrogen Eethinyl Estradiol, is an example.

People take ten tablets with one ratio of the drugs, followed by 11 more at a different rate, and finally seven dummy tablets.

Triphasic pills change the relative levels of the progestin and estrogen compounds twice during the active cycle. “Enpresse,” which contains the progestin levonorgestrel and the estrogen Eethinyl Estradiol, is an example of a triphasic pill.

Some women prefer biphasic and triphasic because they find them to have fewer and milder side-effects.

Progestin-Only Pill (Mini-pill)

These pills contain only progestin compounds, without any estrogenic compounds. They are used by women who are breastfeeding since regular combined pills tend to decrease milk production.

Some people recommend them for the women who are at high risk of dangerous cardiovascular complications from regular contraceptive pills, for example, smokers over the age of 35.

These pills carry a slightly higher risk of pregnancy compared to combined pills.

Emergency Contraceptive Pills

Women can take these pills after sex as an emergency measure. “Plan B One-Step” and “Take Action” are examples. These contain the progestin levonorgestrel.

Despite being known as “morning after” pills, it’s best for women to take such medication as soon as possible; there’s no need to wait until morning.

They can be sufficient for up to three to four days from when intercourse took place, but the chances of pregnancy increase with time.

How useful are contraceptive pills?

Efficacy is a common and primary concern when choosing a contraceptive method.

Birth control pills are quite useful. Combined pills work best when taken every day. People take progestin-only pills at the same time each day. This method keeps the hormone levels in the woman’s body correctly.

Annually, less than one woman in 100 will get pregnant if she always takes the pill every day as directed.

About nine women out of 100 per year will become pregnant if they do not always take the contraceptive pill every day as directed.

The medicine may be slightly less efficient for overweight women. Check with your healthcare provider if you have questions about the effectiveness of the pill in your case.

Certain medications and supplements may decrease the effectiveness of the pill.

These include the following:

  • The antibiotic rifampicin; Other antibiotics do not decrease the effectiveness of the pill.
  • Some medications are taken orally for yeast infection.
  • Certain anti-HIV drugs.
  • Some medicines to prevent seizures.
  • Grass of San Juan.

Vomiting and diarrhea may also prevent the effective action of the pill. Check with your healthcare provider.

Use a backup contraceptive method, such as condoms, female condoms, diaphragms, sponges or emergency contraception (morning after pill) until you are sure you do not need it.

Remember that the pill does not protect against sexually transmitted infections. Use a latex condom or a female condom to reduce the risk of disease.

When should I start taking the birth control pill?

Before, many people told women that they could only start taking the pill on the first day of the menstrual period or the first Sunday after the menstrual period began.

At present we know that it is entirely correct to start taking the pill any day of the month. Talk to your healthcare provider to find out the best day to start taking this medication.

Side-Effects and Benefits

Minor side effects of the contraceptive pill include headaches, nausea, and breakthrough bleeding.

A different brand of the pill may give fewer side-effects. Thrombosis and other cardiovascular problems are more harmful side-effects, which on rare occasions can be fatal.

Women at high risk of thromboses, such as smokers over the age of 35, or those with high blood pressure, should avoid the combination of the pill.

There is some evidence that pills containing drospirenone, such as Yasmin and Yaz, give a higher risk of cardiovascular complications than those containing levonorgestrel. However, the overall risk for anyone woman remains low.

The contraceptive pill also has health benefits. Certain cancers, including ovarian cancer and colon cancer, are less likely to occur if women are taking this medication.

Birth control pills in a nutshell

  • Take one pill a day to prevent pregnancy.
  • It is safe, effective and convenient
  • It’s easy to get a prescription
  • It’s available at a relatively low cost.


1. NHS Website, Combined Pill, see Accessed October 14th, 2014.
2. Medline Plus, Estrogen, and Progestin (Oral Contraceptives) see Accessed October 14th, 2014.
3. Lidegaard, O. et al. BMJ, 2011, vol.343, d6423.