How Effective Are Oral Contraceptives?

Oral contraceptives—most commonly known as "the pill"—are a popular birth control method. Taken by mouth once a day, these pills are intended to inhibit fertility.

Teenage girl with the Contraceptive Pill
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How Oral Contraceptives Work

Most oral contraceptives are taken for 21 days and are then followed by seven days of placebo pills, or simply a seven-day break from taking pills. During these seven days, menstruation normally occurs.

During those initial 21 days, however, your system absorbs the combination of estrogen and progesterone in the pills, which then prevents ovulation (the release of your eggs from your ovaries) from occurring. The lining of your uterus is also affected, and the mucus at your cervix changes as well, so as to prevent sperm from entering the uterus.


The pill is considered to be more than 99% effective when used correctly. In cases where oral contraceptive does fail, it is typically because of user error. This includes forgetting to take one or more active pills, not taking pills at the same time every day or potential interactions with other medications being taken at the same time.

In rarer cases, vomiting or diarrhea, or interaction with other drugs, can decrease the effectiveness of oral contraceptives.

Types of Oral Contraceptives

Different brands of oral contraception contain different proportions of estrogen and progestin. There are even progestin-only pills, which are sometimes called mini-pills. There are also variations in other hormone levels. Finally, some pills are monophasic (delivering the same dose of hormones each day) while others are multiphasic (doses vary each day).

There are even some birth control pills, such as Yaz, that are marketed as being able to reduce the symptoms of premenstrual dysphoric disorder (PMDD: heightened physical and emotional symptoms that occur before menstruation. Others are said to be effective in treating acne. 

If you forget to take your pill, women who have unprotected sexual intercourse may also be prescribed the morning after pill, an emergency contraceptive. Emergency contraception is not an abortifacient and is safe to use.

Other Benefits 

In addition to those pills that are said to treat PMDD or acne, the birth control pill is also sometimes prescribed to treat heavy or irregular menstruation or endometriosis.

Side Effects 

As with most medications, everyone's body can react in a different way. Here is a partial list of the side effects that have been reported by those using birth control pills:

  • Nausea
  • Vomiting
  • Stomach cramps or bloating
  • Diarrhea
  • Constipation
  • Increased or decreased appetite
  • Weight gain or weight loss
  • Acne
  • Hair growth in unusual places
  • Bleeding or spotting between menstrual periods
  • Changes in menstrual flow
  • Painful or missed periods
  • Breast tenderness, enlargement, or discharge
  • Loss of appetite
  • Loss of energy
  • Depression
  • Loss of libido

If you experience these or any other symptoms after beginning to take birth control, consult with your healthcare provider. You may need to try a different brand of oral contraception, with a different mix of hormone levels.

As with any new medical regimen, open communication is key.

By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.