Contraceptive pill, progestogen only

Page last reviewed: 13/07/2011

The progestogen-only contraceptive pill is taken by women to prevent pregnancy.

It contains progestogen, a synthetic (artificial) version of the hormone progesterone that women produce naturally in their ovaries.

The progestogen-only pill differs from the combined contraceptive pill, which contains both female sex hormones oestrogen and progestogen. This makes the progestogen-only pill an option for women who cannot take the combined contraceptive pill, such as those over the age of 35 or those who smoke.

One pack of the progestogen-only pill contains 28 pills. One pill is taken every day of the menstrual cycle.

How effective is it?

When taken correctly, the progestogen-only pill is more than 99% effective at preventing pregnancy. This means that less than one woman in every 100 will get pregnant in a year.

How the progestogen-only pill works

The progestogen-only pill works in two ways:

  • it thickens the mucus in the neck of the womb, so it is harder for sperm to penetrate into the womb and reach an egg
  • it thins the lining of the womb, so there is less chance of a fertilised egg implanting into the womb and being able to grow

Sometimes, the progestogen-only pill may also prevent ovulation (the release of an egg from your ovaries each month).

Types of progestogen-only pill

There are two different types of progestogen-only pill, which must be taken at different times of the day:

  • The three-hour progestogen-only pill must be taken within three hours of the same time each day. Examples are Femulen, Micronor, Norgeston and Noriday.
  • The 12-hour progestogen-only pill (Cerazette) must be taken within 12 hours of the same time each day. It is less commonly used than the three-hour pill.

Page last reviewed: 13/07/2011

The progestogen-only pill can be used by most women. 

When to avoid it

You may not be able to use the progestogen-only pill if you have had:

  • heart disease
  • liver disease
  • breast cancer
  • cysts on your ovaries
  • unexplained vaginal bleeding
  • migraines with aura
  • an ectopic pregnancy (when a fertilised egg begins to develop outside the womb)

If you are healthy and there are no medical reasons why you should not take the progestogen-only pill, you can take it until your menopause or until you are 55.

Breastfeeding

The progestogen-only pill is safe to use if you are breastfeeding. Small amounts of progestogen may pass into your breast milk, but this is not harmful to your baby. The progestogen-only pill does not affect the way your breast milk is produced.

Pregnancy

Although it is very unlikely, there is a very small chance that you could become pregnant while taking the progestogen-only pill.

If this happens, there is no evidence that the pill will harm your unborn baby. If you think you may be pregnant, speak to your GP or visit your local family planning clinic.

Get medical advice if you have a sudden or unusual pain in your abdomen (tummy), or if your period is much shorter or lighter than usual. It is possible that these symptoms are warning signs of an ectopic pregnancy, although this is rare.

Advantages

Some advantages of the progestogen-only pill include:

  • it does not interrupt sex
  • you can use it when breastfeeding
  • it is useful if you cannot take the hormone oestrogen, found in the combined pill, contraceptive patch and vaginal ring
  • you can use it at any age: even if you smoke and are over 35
  • it can reduce the symptoms of premenstrual syndrome and painful periods

Disadvantages

Some disadvantages of the progestogen-only pill include:

  • It can cause temporary side effects at first, such as headaches, nausea, breast tenderness and mood swings. If these do not go after a few months, it may help to change to a different pill.
  • You may not have regular periods while taking it. Your periods may be lighter, more frequent or may stop altogether.
  • It does not protect you against sexually transmitted infections.
  • You need to remember to take it at the same time every day.

Page last reviewed: 13/07/2011

There are 28 pills in a pack of progestogen-only pills. You need to take one pill every day, within either three or twelve hours of the same time each day (depending on which type you are taking).

Starting the first pack of pills

The progestogen-only pill can be started at any time in your menstrual cycle.

It is usually started on the first day of your period (day one of your menstrual cycle). In this case, you will be protected from pregnancy straight away and will not need additional contraception.

You can also start the progestogen-only pill up to, and including, the fifth day of your period and will be protected from pregnancy straight away unless you have a short menstrual cycle (your period is every 23 days or less). If you have a short menstrual cycle, you will need additional contraception, such as condoms, until you have taken the pill for two days.

If you start the progestogen-only pill on any other day of your cycle, you will not be protected from pregnancy straight away and will need additional contraception until you have taken the pill for two days.

After having a baby

If you have just had a baby, the progestogen-only pill can be started on day 21 after the birth. You will be protected against pregnancy straight away.

If you start the progestogen-only pill later than 21 days after giving birth, you will need to use additional contraception (such as condoms) until you have taken the pill for two days.

After a miscarriage or abortion

If you have had a miscarriage or abortion, the progestogen-only pill can be started up to seven days afterwards and you will be protected from pregnancy straight away.

If you start the pill more than seven days after the miscarriage or abortion, use additional contraception until you have taken the pill for two days.

How to take the pill

  • Choose a convenient time in the day to take your first pill.
  • Continue to take a pill at the same time each day until the pack is finished.
  • Start your next pack of pills immediately. There is no break between packs of pills.

Vomiting and diarrhoea

If you vomit within two hours of taking a pill, it may not have been fully absorbed into your bloodstream. Take another pill straight away and the next pill at your usual time.

If the replacement pill is not taken within three hours (12 hours for the 12-hour pill) of your normal time, use additional contraception, such as condoms, for two days.

If you continue to be sick, keep using another form of contraception while you are ill and for two days after recovering.

Very severe diarrhoea (six to eight watery stools in 24 hours) may also reduce the effectiveness of the pill. Keep taking your pill as normal, but use additional contraception, such as condoms, while you have diarrhoea and for two days after recovering.

Speak to your GP or family planning nurse if you are unsure whether or not you are protected or if your sickness or diarrhoea continues.

Page last reviewed: 13/07/2011

The progestogen-only pill is generally well tolerated and side effects are rare. It will not affect your ability to drive or react with any food or alcohol that you consume.

However, you may experience irregular menstrual bleeding, such as:

  • periods that are heavier than usual
  • a missed period
  • breakthrough bleeding and spotting

Some of the other possible side effects of the progestogen-only pill are:

  • acne
  • breast tenderness and breast enlargement
  • an increased or decreased libido (sex drive)
  • mood changes
  • headache and migraine
  • nausea or vomiting
  • cysts (small fluid-filled sacs) on your ovaries (these are usually harmless and disappear without treatment)
  • stomach upset
  • weight gain

These side effects are most likely to occur during the early months of taking the progestogen-only pill, but they generally improve over time and should stop within a few months.

If you have any concerns about your contraceptive pill, see your doctor or nurse. They may advise you to change to another pill or a different form of contraception.

Page last reviewed: 13/07/2011

The progestogen-only pill can interact with other medicines. Some of the more common interactions are listed below. However, this is not a complete list.

If you want to check that your medicines are safe to take with the progestogen-only pill, ask your doctor or pharmacist, or read the patient information leaflet that comes with your medicine.

Antibiotics

The antibiotics rifampicin and rifabutin can reduce the effectiveness of the progestogen-only pill. The other antibiotics do not have this effect.

If you are prescribed rifampicin or rifabutin, you may need to use additional contraception (such as condoms) while you are taking the antibiotic. Speak to your doctor or nurse for advice.

Other medicines

The progestogen-only pill can interact with medicines called enzyme inducers. These speed up how quickly your liver breaks down the hormone progestogen, reducing the effectiveness of the progestogen-only pill.

Examples are:

  • the epilepsy drugs carbamazepine, oxcarbazepine, phenytoin, phenobarbital, primidone and topiramate
  • St John's Wort (a herbal remedy)
  • antiretroviral medicines used to treat HIV (research suggests that interactions between these medicines and the progestogen-only pill can affect the safety and effectiveness of both)

Your GP or nurse may advise you to use an alternative or additional form of contraception while you are taking any of these medicines.

Page last reviewed: 13/07/2011

If you forget to take a progestogen-only pill, what you should do depends on:

  • the type of pill you are taking
  • how late you are taking the pill and how many pills you have forgotten to take
  • whether you have had sex without using another form of contraception during the previous seven days

If you are less than 3-12 hours late

If you are taking a three-hour progestogen-only pill and you are less than three hours late taking it, or you are taking the 12-hour progestogen-only pill and are less than 12 hours late, you do not need to worry.

Take the late pill as soon as you remember and the remaining pills as normal. Your contraceptive protection will not be affected, so you do not need to use any additional contraception.

Do not worry if you have had sex without using another form of contraception. You do not need emergency contraception.

If you are more than 3-12 hours late

If you are taking a three-hour progestogen-only pill and you are more than three hours late taking it, or you are taking the 12-hour progestogen-only pill and are more than 12 hours late, follow the advice below:

  • take the last pill you missed straight away (if you have missed more than one, take only one)
  • take your next pill at the normal time.

Depending on when you remember, it may mean taking two pills on the same day (one at the time of remembering and one at the regular time), or even at the same time.

You will not be protected from pregnancy, so use additional contraception, such as condoms, for the next two days after taking the missed pill.

If you have recently had unprotected sex, you may need emergency contraception. Seek advice straight away from your GP or local sexual health clinic.

The progestogen-only pill is less effective when…

  • it is not taken according to the instructions
  • it does not stay in the body long enough to work, for example because of vomiting or diarrhoea
  • other medicines make it less effective

Page last reviewed: 13/07/2011

The progestogen-only pill is very safe to take. However, as with the combined contraceptive pill, there are certain risks.

Ovarian cysts

Some women can develop fluid-filled cysts on their ovaries. These are not dangerous and do not usually need to be removed. These cysts usually disappear without any treatment.

In many cases the cysts do not cause any symptoms, although some women experience pelvic pain.

Breast cancer

Research is continuing into the link between breast cancer and the progestogen-only pill. Research suggests that users of all types of hormonal contraception have a slightly higher chance of being diagnosed with breast cancer compared with non-users of hormonal contraception. But 10 years after you stop taking the pill, your risk of breast cancer goes back to normal.

If you have a family history of breast cancer, you may feel that this increase in risk (however small it is) is not worth taking. However, doctors do not think that contraceptive pill use is likely to increase the risk present in women who already have close relatives with breast cancer.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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