January 29, 2009

Q&A: Birth Control Pill Effectiveness: How Long Does It Take?

A female reader asks how long it takes for birth control pills to become effective and how to decrease her risk of pregnancy.

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Question: When I first started taking the birth control pill last year, it was just to make my period regular – I wasn’t having sex. Now I am thinking about having sex, but I’m not sure when it’s safe to do so. Can I have sex at any time without getting pregnant as long as I take the pill? Or do I have to wait a while first?

These days, birth control pills (also called oral contraceptives) are used by women for numerous reasons.

Some women start taking oral contraceptives in order to improve their acne. Others start taking the Pill in order to shorten the length of their menstrual periods, regulate their periods or to relieve menstrual symptoms such as headaches or cramps.

Though you first started taking the pill for period-related reasons, you now need information about how it relates to your sex life and your protection against pregnancy.

Usually About One Month

Most birth control pill brands are effective against pregnancy after a woman has taken them consistently for about one month. Depending on the type of pill a woman is taking, and when she starts taking it, the pill may even be effective against pregnancy as early as one full week after starting to take it.

Women who have questions about how soon their pill becomes effective against pregnancy should ask their healthcare provider for more information.

In your case, however, you’ve been taking the pill since last year! Since you’ve been taking the pill for longer than one month, it should already be safe for you to have sex, with a very low risk of pregnancy, assuming that you have been taking the pill every day, as prescribed.

About 97% Effective

With perfect use, the pill is about 97% effective against pregnancy. It is not perfect – no method is – so if you are concerned about becoming pregnancy, you might use a second method of birth control.

For example, some women who are on the pill find that they feel more confident about their pregnancy risk reduction if they also ask their partner to withdraw before ejaculation, or if they use a condom.

An advantage of using a condom is that using condoms can greatly reduce one’s risk of transmitting several sexually transmissible infections, such as chlamydia, gonorrhea and HIV.

Learn More

To learn more about birth control methods, including the pill, check out our birth control and pregnancy resource pages or Planned Parenthood’s web site.

To learn more about your specific brand of birth control, and to ask questions related to your personal health or pregnancy risk, please speak with your healthcare provider.