How the progestogen-only pill works

Dr Juliet McGrattan (MBChB)
·9-min read
Photo credit: AaronAmat - Getty Images
Photo credit: AaronAmat - Getty Images

From Netdoctor

The progestogen-only pill (POP), also known as the mini pill, is the second most commonly used contraceptive in the UK. The mini pill is different from the combined contraceptive pill which contains both progesterone and oestrogen. The mini pill needs to be taken every day, at the same time, without any breaks and when used correctly it is 99 per cent effective at preventing pregnancy.

To help you make an informed decision about contraception, Dr Juliet McGrattan offers her expert advice on the progesterone only pill:

What does the mini pill contain?

Progestogens are synthetic forms of the body’s own hormone progesterone. In the UK, the most common progestogens found in the mini pill are:

Norethisterone and levonorgestrel containing POPs are known as ‘traditional POPs’ in contrast to the newer desogestrel (DSG) mini pills.

How does the mini pill work?

Both traditional and DSG mini pills work by increasing the amount and thickness of cervical mucous. This makes it harder for sperm to swim through the cervix and into the womb and fallopian tubes where they could fertilise an egg. This mucous thickening effect lasts for about 24 hours after the mini pill is taken.

In women who take traditional mini pills, ovulation is suppressed in about 50 per cent of menstrual cycles. This means that the ovaries don’t release an egg. With DSG mini pills however, this rises to 97 per cent of cycles. For this reason, many women choose a DSG mini pill to reduce the risk of pregnancy as much as possible.

It is also thought that the mini pill affects the endometrium (lining of the uterus) making it less likely for a fertilised egg to implant. In addition, they may reduce the ability of the fallopian tubes to waft and move eggs along the tubes towards sperm.

Photo credit: areeya_ann - Getty Images
Photo credit: areeya_ann - Getty Images

How do I take the mini pill?

To give effective contraception, it’s vital that the mini pill is taken correctly:

  • You need to take the mini pill at the same time each day with no breaks between packs.

  • Find a time of day when you can consistently take your pill. For example, don’t choose 7pm if you are frequently out in the evenings.

  • Associate your pill taking with a daily habit such as brushing your teeth or having breakfast. Use a reminder on your phone. Be consistent.

  • Take your pill every day. There should be no breaks, unlike the combined contraceptive pill where breaks are frequently scheduled.

  • You have a three-hour window to take the traditional mini pill and a 12-hour window to take the DSG pills but you should aim for exactly the same time every day to be safe.

When can I start the mini pill?

After a discussion with your doctor or nurse you can start the mini pill at any time in your menstrual cycle as long as there is no chance you could be pregnant.

If you start within five days after the beginning of a normal menstrual period, you are covered for contraception immediately.

After day five you will need to use extra precautions such as condoms, or avoid having sex for 48 hours after you have begun taking the mini pill.

The mini pill can also be started within 21 days of giving birth and within five days of a termination of pregnancy without the need for extra precautions. Beyond those times or when starting the mini pill after using emergency contraception, you must use condoms or abstain from having sex for 48 hours to avoid pregnancy.

How effective is the mini pill?

If you take the mini pill perfectly, then it is 99 per cent effective.

You must take the traditional mini pills within a three-hour window. This means that if you usually take it at 7am you should still be covered for contraception until 10am.

The DSG pills have a 12-hour window so as long as you remember to take it within 12 hours of your usual pill-taking time you should be fine. This longer window coupled with the fact that DSG pills are more likely to suppress ovulation make them a first choice when it comes to the mini pill for most women.

What if I miss the mini pill?

It is important to know what to do if you miss your mini pill to minimise your risk of pregnancy:

  • If you are using a traditional mini pill, your pill is classed as ‘missed’ if you are more than three hours late taking it or it is more than 27 hours since you took your last pill.

  • If you are using a DSG mini pill, then it qualifies as a missed pill if it is more than 12hrs late eg it is more than 36 hours since you took your last pill.

  • Take your missed pill as soon as you realise you have forgotten it. Only take one pill, even if you have missed more than one.

  • Take your next pill at the usual time. This may mean two pills are taken close together but this is OK.

  • Use another method of contraception or avoid having sex for 48 hours after you have restarted your pill.

  • If you have unprotected sex within this 48-hour period, you will need to get emergency contraception. Speak to your pharmacist, local family planning clinic or GP as soon as possible.

If you take your mini pill and then you vomit within two hours of taking it, it will not be absorbed into your system so you should take another one. If your vomiting continues or you miss the next pill you should use extra precautions or avoid having sex for 48 hours after you have restarted your pill.

Is the mini pill right for me?

The mini pill is suitable for most women. There are very few medical conditions that mean you can’t use it. Before it is prescribed, the doctor or nurse will discuss with you whether any of these apply. They include, past or present breast cancer, liver disease, heart disease or stroke.

There are also certain types of medication called ‘enzyme inducers’ which can reduce the effectiveness of the mini pill. These include some anti-epileptic drugs, certain antibiotics and St John’s Wort. Your doctor may recommend another method or additional precautions such as condom use while you are taking the enzyme inducer.

Mini pill advantages

The progestogen-only pill has the following advantages:

✔️ The mini pill is taken every day so it easier to form a habit.

✔️ The mini pill is suitable for many women who are unable to take the combined contraceptive. pill because it does not contain oestrogen.

✔️ The mini pill can be used up to the age of 55.

✔️ The mini pill can help reduce dysmenorrhoea (period pain) and ovulation pain in some women.

✔️ With continued use, 50 per cent of women using DSG mini pills become amenorrhoeic (have no periods) or have infrequent vaginal bleeding.

✔️ There is a quick return to fertility as soon as the mini pill is stopped.

✔️ There is no indication that a single mini pill is less effective in women who are overweight or obese.

Mini pill disadvantages

The progestogen-only pill has the following disadvantages:

✖️ The mini pill needs to be taken at the same time every day.

✖️ Prolonged or irregular vaginal bleeding is common, especially in the early months of using a traditional mini pill.

✖️ The mini pill does not protect against sexually transmitted infections.

✖️ If you have certain medical conditions or are using specific medications the mini pill may not be suitable for you.

✖️ It is possible to fall pregnant very quickly after a missed pill or stopping the mini pill.

The mini pill side-effects

All hormonal contraceptives can give you side effects. Most are minor and are outweighed by the benefits of having reliable contraception.

The most troublesome side effect with the mini pill is a change in bleeding patterns, especially for women using traditional mini pills. These tend to reduce the longer you are on a particular mini pill and are less common in women using DSG pills.

Other side effects include, breast tenderness, headaches and spotty skin. Some women report mood changes, weight gain and loss of libido (sex drive) but medical studies haven’t shown any clear evidence that the mini pill directly causes these.

The mini pill risk factors

We explore the most common risk factors associated with taking contraceptive pills:

Can the mini pill causes breast cancer?

There has not been any clear link proven between using the mini pill and developing breast cancer. There may be a small increased risk but if it exists it is small and likely to reduce when the mini pill is stopped.

Can the mini pill cause ovarian cysts?

While taking the mini pill, some women develop ovarian cysts which are follicles filled with fluid. These are small and tend to disappear on their own and don’t need any treatment. Very occasionally they may cause pelvic pain or discomfort.

Does the mini pill affect heart health?

So far there has been no proven association between taking the mini pill and cardiovascular disease such as heart attacks or strokes. More studies are being done to confirm this.

Can the mini pill cause ectopic pregnancies?

The mini pill is an effective contraceptive but in the small number of women who do become pregnant while taking them there is a 10 per cent risk that the pregnancy will be ectopic. Ectopic pregnancies grow outside of the uterus and can’t continue. They can be life threatening to the mother.

When I’m using the mini pill, how often do I need to see the doctor?

Your doctor or nurse will be able to issue you with a 12-month supply of the mini pill if you are happy with it. If there are any concerns or you are having side effects they may issue a smaller supply and ask you to come back for a review.

When you see your nurse or doctor for a review they will ask you if you are managing to take the mini pill correctly, what your bleeding pattern is like and whether you are having any problems. They will check that you haven’t developed any new medical conditions that might affect the safety of using the mini pill. They will also remind you if you are due for a cervical screening appointment and discuss whether you are at risk of sexually transmitted infections.

Sexual health resources

For further advice and information on choosing the right contraceptive for you, try one of the following:

Last updated: 20-01-2021

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