Do birth control pills work?

November 2, 2022

How do birth control pills work?

Oral contraceptives, also known as birth control pills, are medications taken to prevent pregnancy. Different types of pills work in different ways, but in general, they reduce the chances of pregnancy by:

  • Preventing ovulation – your ovaries do not release an egg each month
  • Thickening the cervical mucus – to prevent sperms from reaching the uterus
  • Thinning the endometrium – to make it harder for a fertilized egg to be implanted on the endometrium

Birth control pills are usually taken each day (at around the same time) for a certain period of time depending on the cycle of the pill you choose, followed by inactive pills – during which menstruation will occur.

Note: Some pill packs do not have inactive pills.

What are the types of oral contraceptive pills and how do they differ?


Mechanism of Action

For the combination pill and progestin-only pill, the pills come in packs of 21 or 28.

  • Monophasic 21-day pills
    • The pills all contain equal amounts of hormones
    • One pill is taken daily for 21 days
    • For the remaining 7 days (when menstruation occurs), no pills are taken
  • For phasic 21-day pills
    • The pills are split into 2-3 sections, with each section containing pills with different amounts of hormones
    • The pills are to be taken in the correct order
    • Similar to the monophasic pills, one pill is taken daily for 21 days
    • For the remaining 7 days (when menstruation occurs), no pills are taken
  • For every day pills
    • There are 28 pills in the pack, 21 active (with hormones), and 7 inactive (without hormones)
    • One pill is taken each day without any break
    • From days 1-7 of your menstruation cycle (when bleeding occurs), take 1 inactive pill daily
    • For the next 21 days, take 1 active pill daily

There are also continuous and extended use pills.

  • Continuous use pills (365-day pills)
    • One pill is taken daily for a year or longer with no breaks
    • Menstrual bleeding may become lighter/ stop altogether
  • Extended use pills (91-day pills)
    • Pills are taken for more than the usual 21 days (usually 91 days)
    • One pill is taken daily for the first 84 days
    • For the last 7 days (when menstruation occurs), inactive pills will be taken

What are some common ways to start on my pill?

If you are sexually active but do not wish to have children (yet), do consider consulting your doctor about starting on birth control pills. To ensure that you are fit to take birth control pills, your doctor will first take your blood pressure, check for any sexually transmitted infections (STIs) and ensure that you are not pregnant.

Next, you will be introduced to the different types of birth control pills (their cycles, advantages, side effects, etc.) before you choose the one that is most suitable for you. After you receive the pills that your doctor has prescribed, you can start on the pill!

Here are some common ways to start on the pill:

  • First day start
    • On the day you get your period, take your first birth control pill
    • You will not need a second contraception method if you are on your period
  • Quick start
    • Take your first birth control pill right away
    • You will need to use a second contraception method (e.g. condom) when engaging in sexual activity for the next 7 days, as the hormones in the pills that prevent pregnancy need time to take effect
    • Generally, not recommended

What do I do when I miss a pill?

You missed one pill only (you did not take it at the same time as the previous day)

Take your pill as soon as you remember; if you only remember the next day, take 2 pills that day. However, the next 7 days do use additional barrier contraceptive methods.

If you miss pills for more than 2 days, consult your doctor for more advice.

Do note that anytime you miss your pill(s), another contraceptive method should be used until you finish the pill pack.

Do not worry if you forget to take your inactive pills: your chances of pregnancy will not be increased, as these pills contain inactive ingredients and only serve as placeholders to help you remember to take your pills daily.

What are some benefits of taking birth control pills?

Aside from preventing unwanted pregnancies, there are many other benefits that come with taking birth control pills (both combination and progestin-only pills), which include:

  • Making your period lighter and more regular (easier to predict)
  • Reducing acne
  • Reducing menstrual cramps
  • Lowering your risk of ectopic pregnancy
  • Safely skipping your period

For combination pills, more benefits include preventing or lessening:

  • Bone thinning
  • Cysts in your breasts/ ovaries
  • Ovarian/ endometrial cancers
  • Serious infections in your ovaries/ fallopian tubes/ uterus
  • Iron deficiency
  • Premenstrual syndrome (PMS)

What are some side effects of being on the pill?

Most side effects are mild and temporary. Some include:

  • Breakthrough bleeding – any bleeding/ spotting that occurs when you are not on your period
  • Nausea/ headache
  • Abdominal cramping
  • Breast tenderness
  • Increased vaginal discharge
  • Decreased libido

How effective are birth control pills?

A. Combination pill

  • Perfect use
    • More than 99% effective
    • Fewer than 1 in 100 women will get pregnant yearly
  • Typical use
    • Around 91% effective
    • Around 9 in 100 women will get pregnant yearly

B. Progestin-only pill

  • Perfect use
    • Around 99% effective
    • Around 1 in 100 women will get pregnant yearly
  • Typical use
    • Around 91% effective
    • Around 9 in 100 women will get pregnant yearly

How do morning after pills work?

This pill is an emergency contraception that:

  • Delays/ inhibits ovulation if that event has not occurred yet
  • Irritates the endometrium to prevent implantation of fertilised egg

It is taken to prevent pregnancy after unprotected sex – if any of the following occur:

  • Condom broke/ came off during sex
  • You/ your partner did not use a condom
  • You did not take a birth control pill

Some side effects include:

  • Nausea/ vomiting
  • Dizziness
  • Fatigue
  • Headache
  • Breast tenderness
  • Bleeding/spotting between periods
  • Heavier menstrual bleeding
  • Stomach cramps


  • 95% when taken 24 hours after unprotected sex
  • 85% when taken between 25-48 hours after unprotected sex
  • 58% when taken 48 hours after unprotected sex

For more information or if you require a medical consultation, please contact My Healthcare Collective here.

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