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When you take the pill every single day, it’s great at preventing pregnancy. But missing pills, taking certain medications, and other things may make it not work as well.

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How effective is the birth control pill?

If you use it perfectly, the pill is 99% effective. But people aren’t perfect and it’s easy to forget or miss pills — so in reality the pill is about 91% effective. That means about 9 out of 100 pill users get pregnant each year.

The better you are about taking your pill every day and starting your pill packs on time, the better the pill will work. You can use our birth control app to remind you to take your pills when you need to. But there’s a very small chance that you could still get pregnant, even if you always take your pills correctly.

If you want a method that’s even better at preventing pregnancy, you might want to check out IUDs and the implant. They’re the best at preventing pregnancy.  But if you decide the pill is right for you, make sure you always take your pills on time so they work as well as possible.

What lowers the birth control pill’s effectiveness?

The main thing that makes the pill not work is not taking it every day. But other things, like vomiting or having diarrhea for more than 48 hours (2 days) may lower how well the pill prevents pregnancy. 

These medicines or supplements can also make the pill not work as well:

• The antibiotic Rifampin (other antibiotics don’t make the pill less effective)

• The antifungal Griseofulvin (other antifungals don’t make the pill less effective)

• Certain HIV medicines

• Certain anti-seizure medicines (these are sometimes also used to treat psychiatric disorders like bipolar disorder)

• The herb St. John’s Wort

If you take any of these while you’re on the pill, use condoms as a backup method. Switch to a different method of birth control if you’ll be on them for a long time.

Your nurse or doctor can help you decide if there’s any reason the birth control pill won’t work well for you.

How long do birth control pills take to work?

It depends on when you start taking them and what type of pills you’re using. You can start taking the birth control pill any day of the month. But depending on when you start and the kind of pill you’re using, you may need to use a backup birth control method — like condoms — for up to 7 days.

Combination Pills (COCs)

  • If you start combination pills within 5 days after the first day of your period, you’ll be protected from pregnancy right away. For example, if you get your period Monday morning, you can start the pill anytime until Saturday morning and be protected from pregnancy that same day.

  • If you start combination pills any other time, you need to take the pill for 7 days before you’ll be protected from pregnancy. So use another method of birth control — like a condom — if you have penis-in-vagina sex during your first week on the pill.

Progestin-Only Pills (Mini Pills)

  • You can start progestin-only pills any day of the month. You’ll be protected from pregnancy after 48 hours (2 days). So use another method of birth control (like condoms) if you have penis-in-vagina  sex during the first 48 hours.

Your nurse or doctor can help you figure out the best time to start your birth control pills, and when they’ll start working.

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The Pill

  • 91% effective

  • Costs up to $50, but can be $0

  • Prescription required

  • Take once a day

The pill doesn’t protect you from  STDs. Use a condom with your pill to help stop pregnancy and STDs.
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