A Guide To The Progesterone-only Pill

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The progestogen-only pill (POP) is a method of contraception that contains the hormone progestogen but does not contain oestrogen. You must take the progestogen-only pill at the same time every day.

If taken correctly, it can be more than 99% effective. The progestogen-only pill is particularly suitable for women who cannot use contraception that contains oestrogen. It is also a good choice if you have high blood pressure, have had previous blood clots, are overweight or smoke after the age of 35.


How Does The Progesterone-only Pill Work?

The POP works by thickening the mucus around the cervix (neck of the womb), which stops sperm from penetrating the uterus and reaching an egg.

The progestogen hormone in older (traditional) POPs is either levonorgestrel or norethisterone. Brands currently available in the UK are Micronor, Noriday and Norgeston. A newer type of POP contains a progestogen hormone called desogestrel. Brands currently available include Cerazette, Aizea, Cerelle and Feanolla.

Progestogen-only pills that contain desogestrel can stop ovulation (when an egg is released from the ovary). Non-desogestrel pills stop ovulation about 60% of the time while desogestrel pills stop ovulation about 97% of the time.


When To Start Taking The Progesterone-only Pill

You can start the progestogen-only pill at any time in your menstrual cycle. If you start the progestogen-only pill on day 5 of your menstrual cycle or earlier (the fifth day after the start of your period or before) you will be protected from pregnancy straight away. If you start the progestogen-only pill on any other day of your cycle, you will not be protected and will need extra contraception (such as condoms) until you have taken the pill for 2 days.

If you have just had a baby, you can start the progestogen-only pill on day 21 after giving birth and you will be protected against pregnancy straight away. If you take the POP more than 21 days after giving birth, you will need to use condoms for 2 days. The progestogen-only pill is safe to use if you are breastfeeding.

If you have had a miscarriage or abortion, you will be protected from pregnancy if you take the POP within 5 days. If you start the pill more than 5 days after a miscarriage or abortion, you will need to use condoms for 2 days.


How To Take The Progesterone-only Pill

You should take a pill at the same time every day, with no break between packs of pills. It is important to follow the instructions on your pill packet instructions. Missing pills or taking the pill with other medicines can reduce its effectiveness.

There are 28 or 35 pills in a pack of progestogen-only pills. You should take 1 pill every day, within either 3 or 12 hours of the same time each day (depending on which type you are taking). There is no break between packs of pills - when you finish one pack you will take a pill from the next pack the following day.


There are 2 different types of progestogen-only pills:

  • A 3-hour progestogen-only pill must be taken within 3 hours of the same time each day.
  • 12-hour progestogen-only pill (desogestrel pill) must be taken within 12 hours of the same time each day (brands include Aizea, Cerazette, Cerelle and Desomono)

When starting to take the progesterone-only pill, you should choose a convenient time in the day to take your first pill as you will need to continue taking your pill at the same time each day until the pack is finished.


When The Progesterone-only Pill Is Not Effective

The situations in which the progesterone-only pill may not be effective include:

  • If you take it more than 3 hours late (or 12 hours late if you take a desogestrel pill) it may not be effective. If you had sex around the time you missed your pill, you may need emergency contraception. You should seek advice from your GP, nurse or pharmacy,
  • If you vomit (are sick) or have severe diarrhoea (runny tummy), the progestogen-only pill may not work.
  • Some medicines may affect the progestogen-only pill's effectiveness. These include some medications for HIV and epilepsy, the herb St John's Wort, rifabutin (used to treat tuberculosis) and rifampicin (used to treat tuberculosis and meningitis).
  • The progestogen-only pill does not protect against sexually transmitted infections (STIs). 

Advantages Of The Progesterone-only Pill

The Progesterone-only Pill has many benefits for women who are unable to take other forms of contraception. It is a convenient and safe method of birth control that is over 99% effective when used correctly. Other benefits of the POP include:

  • You can start the progestogen-only pill at any time in your menstrual cycle.
  • You can take the POP if you are overweight, smoke or are older than 35.
  • Your periods may stop or become lighter.
  • It is suitable for almost everyone, even if they have health conditions.
  • You can take it until your menopause or until you are 55.
  • It is useful if you cannot take the hormone oestrogen.
  • You can take it while breastfeeding.


Disadvantages Of Taking The Progesterone-only Pill

The side effects associated with taking the POP are normally mild and are most likely to occur during the first few months. Symptoms usually improve over time and should stop within a few months.


Possible side effects when taking the progesterone-only pill include:

  • Your periods may become irregular or more frequent.
  • Side effects may include spotty skin and breast tenderness although these normally clear up within a few months.
  • Acne
  • Breast tenderness and breast enlargement
  • An increased or decreased sex drive (libido)
  • Mood swings
  • Headache and migraine
  • Nausea or vomiting
  • Ovarian cysts (small fluid-filled sacs on your ovaries) - they usually disappear without treatment
  • Women who use hormonal contraception have a slightly higher chance of developing breast cancer.
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