I’ve missed a Cerazette pill, what’s the risk of getting pregnant?

Cerazette is a type of progesterone-only contraceptive pill that, as the name suggests, only contains a synthetic version of the hormone progesterone.

There are several different brands of progesterone-only pill (POP) available, and Cerazette is one of them.¹

When used correctly, POPs are over 99% effective.² But what happens when you don’t take it correctly?

It can be worrying if you have missed a pill and are concerned you may become pregnant, so it’s useful to understand both how Cerazette works and the risk of pregnancy if you forget to take it.

How does Cerazette work?

Several hormones, including progesterone, play a role in the menstrual cycle and fertility. Various changes happen within the body in relation to our cycle each month.

Contraceptives containing hormones prevent pregnancy by causing changes which already happen naturally in the body, but at different points of the menstrual cycle.

There are two main ways that Cerazette does this. The first is by increasing the amount and the thickness of a person’s cervical mucus.³

Normally, when an egg is released by the ovaries, cervical mucus becomes clearer and thinner (a bit like the consistency of egg whites).⁴ This is to allow sperm to pass from the vagina, through the mucus, and through the cervix into the womb, ready to fertilise an egg.

Cerazette is a newer type of progesterone-only pill, which is better at stopping an egg from being released and suppresses ovulation in up to 97% of menstrual cycles in people using it

By increasing the volume and thickness of cervical mucus, Cerazette keeps the mucus in the “non-fertile” state, which prevents the sperm from being able to pass into the womb. This stops fertilisation from occurring.

Cerazette also works to prevent pregnancy by stopping the release of an egg from the ovaries.⁵ In a menstrual cycle, the levels of different hormones fluctuate throughout, and these influence the development and release of an egg.⁶

Progesterone levels are naturally higher later on in the menstrual cycle, after ovulation has occurred — i.e. when no eggs are ripening in the ovary. Levels are also high during pregnancy when no eggs are being released at all.⁷ As Cerazette contains progesterone, it keeps the body’s levels of progesterone consistently high, stopping the development and release of an egg.

It is important to note that different POP brands prevent the release of eggs to varying degrees. Cerazette is a newer type of progesterone-only pill, which is better at stopping an egg from being released and suppresses ovulation in up to 97% of menstrual cycles in people using it.⁸

Combined with the effect on mucus from the cervix, if Cerazette is used correctly, it is over 99% effective at preventing pregnancy.⁹ Cerazette should be taken every day at the same time.¹⁰

What if I’ve missed a pill?

If you’ve missed a Cerazette pill, the risk of pregnancy depends mainly on two factors: how long it has been since you last took a pill and when you last had unprotected sex (defined here as penis-in-vagina sex).

If you take your forgotten pill up to 12 hours after the time you’d normally take it, it doesn’t count as missed.¹¹

This means that if you have not taken your pill at your regular time, but you are still within 12 hours of this, the risk of pregnancy is very minimal — even if you have had unprotected sex during this time.

You should take the missed pill as soon as you remember and take your next pill at the usual time you take it

Within the 12 hour window, the pill is still effective at preventing ovulation, even though its effects on cervical mucus may start to wear off. For this reason, the POP is still considered effective, and you don’t need to use another contraceptive during this time.

You should take the missed pill as soon as you remember and take your next pill at the usual time you take it.

No extra precautions are needed to prevent pregnancy in this scenario, even if you carried on having unprotected sex — however, barrier methods like condoms are still advised to protect against STDs!

What if I’ve missed the 12-hour window?

In the case that you’ve passed the 12 hour window for taking the missed pill, it is recommended that you take one pill as soon as you remember, and resume taking your next pill at the usual time you take it. This might mean that you take two pills on the same day.

In this case, extra precautions should be taken for the next 2 days if you have sex. For example, you could use a barrier method of contraception such as condoms or avoid penis-in-vagina sex.¹² This is because hormone levels drop when you miss a pill, which increases the risk of pregnancy.

The good news is that Cerazette starts working again pretty quickly once taken; it only takes two days to thicken cervical mucus and this is why the precautions are only needed for this time

Once the effects of the pill wear off, your risk of pregnancy is the same as if you weren’t taking any contraception at all.

However, the good news is that Cerazette starts working again pretty quickly once taken; it only takes two days to thicken cervical mucus and this is why the precautions are only needed for this time.¹³

If you have unprotected sex after missing a pill, emergency contraception is recommended. This is when there’s an increased risk of pregnancy because the effects of the pill will have worn off.

You can access emergency contraception from your GP, sexual health clinic or pharmacist — or even online, depending on where you live. When getting emergency contraception you should mention that you take Cerazette, as this can affect the type of emergency contraception that’s recommended to you.¹⁴

Are there side effects to missing a pill?

Missing a pill can increase the likelihood of irregular vaginal bleeding, due to the change in hormone levels.¹⁵

It is also important to note that diarrhoea and vomiting, and some medications, can affect how well Cerazette works. You can find more advice on this on the NHS website.

If you are concerned or unsure about the risk of pregnancy or require emergency contraception, you can speak to your pharmacist, nurse, GP. You can also call NHS 111 or the national sexual health helpline for free on 0300 123 7123.

Featured image is an illustration of a purse with a zip that’s open, with a full pill packet popping out of it. The purse is semi-transparent so that you can see the packet clearly inside

Page last updated March 2022
Next update due 2025