Progestogen-Only Pill

The progestogen-only pill (POP) is a type of contraceptive pill that only contains progesterone. The POP is taken continuously, unlike the cyclical combined pills. It is more than 99% effective with perfect use, but less effective with typical use (91%).

The progestogen-only pill has far fewer contraindications and risks compared with the combined pill. The only UKMEC 4 criteria for the POP is active breast cancer.



There are two types of POP to remember:

  • Traditional progestogen-only pill (e.g. Norgeston or Noriday)
  • Desogestrel-only pill (e.g. Cerazette)

The traditional progestogen-only pill cannot be delayed by more than 3 hours. Taking the pill more than 3 hours late is considered a “missed pill”.

The desogestrel-only pill can be taken up to 12 hours late and still be effective. Taking the pill more than 12 hours late is considered a “missed pill”.


Mechanism of Action

Traditional progestogen-only pills work mainly by:

  • Thickening the cervical mucus
  • Altering the endometrium and making it less accepting of implantation
  • Reducing ciliary action in the fallopian tubes


Desogestrel works mainly by:

  • Inhibiting ovulation
  • Thickening the cervical mucus
  • Altering the endometrium
  • Reducing ciliary action in the fallopian tubes


Starting the Pill

Starting the POP on day 1 to 5 of the menstrual cycle means the woman is protected immediately.

It can be started at other times of the cycle provided pregnancy can be excluded. Additional contraception is required for 48 hours. It takes 48 hours for the cervical mucus to thicken enough to prevent sperm entering the uterus.

The POP can be started even if there is a risk of pregnancy, as it is not known to be harmful in pregnancy. However, the woman should do a pregnancy test 3 weeks after the last unprotected intercourse. Emergency contraception before starting the pill may be considered if required.

TOM TIP: It takes 48 hours before the progestogen-only pill thickens the cervical mucus enough to prevent sperm entering the uterus, protecting against pregnancy. The combined pill takes seven days before the woman is protected from pregnancy, as it works by inhibiting ovulation rather than thickening the cervical mucus. Therefore, additional contraception is required for 48 hours with the POP and seven days with the COCP when starting after day 5 of the menstrual cycle. Both can be started within the first 5 days of the menstrual cycle and work immediately, as it is very unlikely a woman will ovulate this early in the cycle.


Switching Pills

Switching between POPs

POPs can be switched immediately without any need for extra contraception.


Switching from a COCP to a POP

When switching from a COCP to a POP, the directions depend on what point they are in the COCP pill packet.

They can start the POP immediately, without additional contraception, if they:

  • Have taken the COCP consistently for more than 7 days (they are in week 2 or 3 of the pill pack)
  • Are on days 1-2 of the hormone-free period following a full pack of the COCP


The rules for days 3-7 of the hormone-free period and days 1-7 of taking the COCP depend on whether they have had unprotected sex since day 3 of the hormone-free period.

If they have not had unprotected sex since day 3 of the hormone-free period, they can start the POP immediately but require additional contraception (e.g., condoms) for the first 48 hours of taking the POP.

If they have had unprotected sex since day 3 of the hormone-free period, they should take the COCP until they have taken 7 days consecutively, after which they can switch over to the POP without any additional requirements.

Theoretically, taking the COCP for 7 consecutive days inhibits ovulation for the next 7 days. The POP does not reliably prevent ovulation and works mainly by thickening the cervical mucous. Sperm can live for 5 days in the uterus. Therefore, if the woman has unprotected sex on day 3 or later of the hormone-free period after taking the COCP, sperm can enter the uterus and live there for 5 days (until the 8th day after finishing the COCP). Taking the POP during this time will make no difference to the sperm already in the uterus, as they are already past the cervix. Then, if the woman ovulates on the 8th day after finishing the COCP, those sperm are there waiting to fertilise the egg.


Side Effects and Risks

Changes to the bleeding schedule is one of the primary adverse effects of the progestogen-only pill. Unscheduled bleeding is common in the first three months and often settles after that. Where the irregular bleeding is persistent (for longer than 3 months), other causes need to be excluded (e.g. STIs, pregnancy or cancer).


  • 20% have no bleeding (amenorrhoea)
  • 40% have regular bleeding
  • 40% have irregular, prolonged or troublesome bleeding


Other side effects include:

  • Breast tenderness
  • Headaches
  • Acne


There is also an increased risk of:

  • Ovarian cysts
  • Small risk of ectopic pregnancy with traditional POPs (not desogestrel) due to reduce ciliary action in the tubes
  • Minimal increased risk of breast cancer, returning to normal ten years after stopping


TOM TIP: The bleeding pattern that a woman will experience with progestogen-only contraception (the pill, implant or injection) is unpredictable. To make it simple to remember I round the risks into thirds, with a third having lighter, less regular or no bleeding, a third having normal bleeding and a third having unscheduled, heavier or more prolonged bleeding. It is not possible to predict how individuals will respond. Irregular or troublesome bleeding often settles after three months, so it may be worth persisting. 


Missed Pills

A pill is classed as “missed” if it is:

  • More than 3 hours late for a traditional POP (more than 26 hours after the last pill)
  • More than 12 hours late for the desogestrel-POP (more than 36 hours after the last pill)

The instructions are to take a pill as soon as possible, continue with the next pill at the usual time (even if this means taking two in 24 hours) and use extra contraception for the next 48 hours of regular use. Emergency contraception is required if they have had sex since missing the pill or within 48 hours of restarting the regular pills.

Episodes of diarrhoea or vomiting are managed as “missed pills”, and extra contraception (i.e. condoms) is required until 48 hours after the diarrhoea and vomiting settle.


Last update August 2020