The effectiveness of the pill: How long does it take to work?

Let's examine exactly what "effectiveness" means.
Written by
Rachael Belfield
Reviewed by
Last updated on
June 3, 2024
min read
The Pill Effectiveness: How Long Does It Take to Work? | Kin Fertility
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More than 80% of Australian women use oral contraceptive pills [1]. But it's the almighty combination birth control pills that take the winnings for the most favoured form of birth control. For over 60 years, the pill has been preventing millions of pregnancies with an effectiveness rate of 99% [2].

The pill is non-invasive, convenient and affordable. Hard to beat, right?

The effectiveness of the pill is incredibly high, marred only by a few instances including human error (i.e. if you forget to take a pill). But did you know that to keep birth control's effectiveness up, you have to be strategic about when you start taking the pill?

This will also be dependent on which kind of pill you take. So, while birth control pills are the option we reach for the most, let's examine exactly what "effectiveness" means.

Types of birth control pills

There are 2 types of birth control pills. Both pills prevent pregnancy with high effectiveness rates, but both work in different ways.

The combined pill

This is the pill invented in 1960: the OG, revolutionary, explosive push of progress for women's reproductive choices.

Quite simply, the combined pill contains artificial versions of the female hormones oestrogen and progesterone. These hormones are produced naturally in the ovaries, which perform different functions during different stages of a woman's cycle.

A 28-day pack of combination pills will also include 7 placebo pills (also known as inactive pills or "sugar pills" as they are usually made from sugar) in order for women to continue having their period. While taking the pill continuously and skipping your period is perfectly safe, it might be good to check with your doctor to see how that might impact your body.

The mini pill

The mini pill is the combined pill's oestrogen-less counterpart. It contains a synthetic version of the female hormone progesterone, called progestin. This is an excellent alternative for women who might have negative physical side effects from the added oestrogen in the combined pill.

Unlike the combined pill, there is no 7-day break for your period to come through. The mini pill often leaves people without a period at all, but this is different for every person (some people still bleed).

In a nutshell, with the help of a low dose of progestin, the body works really hard to stop the egg from being fertilised.

How do birth control pills work to prevent pregnancy?

The combined pill prevents pregnancy in a few ways:

  1. The release of oestrogen and progesterone will halt ovulation (the release of an egg from your ovaries each month). This means an egg is not released from the ovaries into the fallopian tubes for fertilisation.
  2. It thins the lining of your uterus, essentially making it an environment incapable of nurturing a fertilized egg (if one were to exist).
  3. The pill also thickens a woman's cervical mucus, so the sperm can't fertilise eggs. It becomes too thick for a sperm to penetrate and the gates stay locked, keeping sperm at bay.

The mini pill essentially does the same as the combined pill: it thickens the mucus in the neck of the womb, making it impossible for sperm to penetrate into the womb and reach an egg for fertilising. It also thins the lining of the uterus, meaning an egg can't sit comfortably in there [3].

However, just to make things a little confusing, not everyone stops ovulating after taking the mini pill. About 40% of women will still ovulate whilst taking the progestogen-only pill. This is why it's of paramount importance that you take the pill at the same time every day.

While the pill and mini pill are both highly effective at preventing pregnancy, they are not effective at all in the prevention of STIs. To avoid STIs, remember to use condoms as a protective measure here.

How long does it take for the pill to work?

So, you've decided to take birth control pills. Yay! But the question remains, when do birth control pills start working after we first take them?

Well, as one pill contains 1 hormone and the other contains 2, both will work a little differently in terms of being effective at preventing pregnancy [4].

The combined pill

It's recommended that you do not rely solely on the pill for contraception until you have taken it at the same time every day for the first 7 days of your menstrual cycle. For these first 7 days, condoms should also be used as an extra protective factor [5].

The mini pill

The mini pill works a little differently from the combined pill — they are immediately effective if started during the first 5 days of your menstrual cycle. If you start the mini pill at any other time during your menstrual cycle, these pills will start to work after you have taken the first 3 pills correctly.

When can I start taking the pill after I have a baby?

If you have just had a baby, and are not breastfeeding, it's recommended you wait until roughly 21 after the birth to start the pill [7]. At this point, you will be protected against pregnancy straight away.

If you start the pill later than 21 days after giving birth, you will need additional contraception (such as condoms) for the next 7 days.

If you are breastfeeding, the combined pill is not recommended until at least 6 weeks after the birth. This is because the high levels of oestrogen work against milk production, and you could be at risk of drying up your milk. Once you've established a good supply of milk for your baby, then the combination pill can be introduced as a form of birth control while breastfeeding.

The mini pill, however, is safe to take after pregnancy and will not affect milk production. Remember, taking either kind of oral contraception should be discussed first with your doctor, especially after birth.

How do you know if birth control is working?

One of the major downsides (or upsides??) is that you usually can't tell if the combined pill or mini pill is working — there are no internal alarms or green signals to let you know that it's doing its job.

The best measure for birth control pills is that no news is good news: if you are not experiencing any adverse side effects, it's probably working.

Nausea is a common side effect of taking the pill for the first time: the high dose of these hormones can irritate the stomach. This usually means the pill or mini pill is doing its job and your body is getting used to it.

Remember that sometimes the effectiveness of the combined pill is lowered if you experience:

If you need to take these medications, speak to your doctor about how they will affect the pill or mini pill and consider using condoms as an extra preventative measure [8].

And, of course, if you forget to take the pill, this will also decrease the birth control's effectiveness. This is especially true for progestin-only pills [4].

Are you protected on the 7-day break from the pill?

Yes. The combined oral contraceptive pill is still a highly effective form of birth control, even as it allows for your period to come through. It's designed to allow for a period to come through while maintaining its effectiveness, as it works within the menstrual cycle. But, you must take this break at the correct time of the month.

Remember, there are no side effects to taking the pill continuously if you would rather skip your period.

The mini pill, however, does not include a 7-day break — you must continue taking the mini pill every day for the 28 days of your cycle.

Whether you're taking the combined pill or the progestin-only pill, you may still have breakthrough bleeding. Every single woman's cycle is different from the next, so it can be hard to pinpoint exactly what kind of effect it will have on the body. A bit of trial and error may be required until you find the right type of birth control you like!

The good news is you'll never forget your pill script with Kin Fertility's contraceptive pill subscription. Australia’s first birth control pill subscription service delivers your oral contraceptive pills straight to your door in a safe and convenient manner.

Together with an Australian practitioner, find the pill that works best for you (plus, each one comes in a shiny pill sleeve!) and your subscription is automatically filled and delivered to you so you'll never run out. Plus, you can access unlimited digital consults with your practitioner when needed.

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