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Birth Control Pill

Your doctor can prescribe birth control pills to prevent pregnancy. When taken properly, birth control pills are 99 per cent effective. The pill doesn't protect you against sexually transmitted infections.

Birth control pills contain low doses of both estrogen and progestin. One type contains progestin alone. These hormones are similar to the natural hormones that control a woman's menstrual cycle. Different brands of pills contain different amounts of estrogen and progestin. Changing the brand of pill can prevent side effects in some cases. When a woman takes birth control pills:

  • her ovaries stop releasing eggs
  • the mucus in her cervix gets thick making it harder for sperm to enter
  • the lining of the uterus gets thinner making it hard for a fertilized egg to attach to the wall

How to Use Birth Control Pills

There are many types of birth control pills. Most brands come as 21-day or 28-day packs. A 28-day pack contains 21 birth control pills and seven sugar pills, and a new 28-day pack is started as soon as the old one is finished. A 21-day pack contains 21 birth control pills. After taking these 21 pills, wait seven days before starting a new 21-day pack. Read the instructions in the package and follow them carefully. For birth control pills to be most effective, you should take your pill at the same time each day.

Some things may stop the pill from working properly. The pill may not work as well:

  • during the first cycle when you are taking birth control pills for the first time
  • during the first cycle when you are taking birth control pills again after being off them
  • if you take a birth control pill more than four hours late (Check our frequently asked questions section for more information about missing a pill)
  • if you are taking antibiotics, antacids or medication that controls seizures (If your doctor gives you any new medication, ask if it will interfere with your birth control pills)
  • if you have vomited or had diarrhea

If these things happen when you are taking the pill, you should use another method of birth control as back up for one full week so you don't get pregnant.


  • very effective at preventing pregnancy
  • your period is regular and sometimes lighter
  • you may bleed less during you period
  • you don't have to interrupt sex
  • the woman controls this method of birth control
  • may decrease menstrual cramps or pain
  • may help control the pain associated with endometriosis


  • you are not protected against sexually transmitted infections
  • you need a prescription
  • you must remember to take it at the same time every day
  • you may have side effects
  • women with some health conditions cannot take birth control pills


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Miss taking a pill, or forget to take your contraceptive dose on time?

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Use the S.O.S. tool created by Sexualityandu.ca, and see what measures you can take to reduce the risk of an unwanted pregnancy.

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