Progestogen only pills are generally less effective than other forms of oral contraceptive pill with a failure rate of 2 - 6 per 100 women years. They are supplied in packs of 28 or 42 and taken daily throughout the menstrual cycle.
- a review (1) has stated however that '..If used consistently and correctly, POPs are more than 99% effective...'
The POP has several independent modes of action that contribute to its contraceptive effect (1)
- POPs increase the volume and viscosity of cervical mucus preventing sperm penetration into the upper reproductive tract. This change occurs soon after starting a POP and it is advised that 2 days of pill taking is sufficient to achieve this element of contraceptive protection. However, the contraceptive effect provided by changes to cervical mucus is also short-lived, unless maintained by regular pill taking. It has been estimated that full protection conferred via cervical mucus may last for less than 24 hours (1)
- POPs can also act to suppress ovulation. The extent to which this occurs is variable; for example, up to 60% of cycles in women using an pill levonorgestrel are anovulatory, whereas ovulation is suppressed in up to 97% of cycles in women using the desogestrel pill
- other modes of action include endometrial changes that hinder implantation, and reduction in cilia activity in the fallopian tube that slows the passage of an ovum
The main side effects are irregular, low-grade, breakthrough uterine bleeding but this may settle into a regular cycle after 6 - 9 months. Other complications include skin reactions, breast fullness and depression. There is an increased risk of ectopic pregnancy*. Also there may be a slight increased in breast cancer associated with the progestogen only pill.
Advantages include:
- do not carry risk of thromboembolism
- do not inhibit lactation - so can use when breast feeding
- suitable for diabetics - as pills containing oestrogen exacerbate risk of arterial disease in such patients
- suited to women for whom oestrogen containing formulations are contra-indicated i.e. the elderly smoker
The dose of progestogens in the mini pill is much smaller than those found in preparations of the combined oral contraceptive pill.
Dose and frequency of administration (2):
- Single tablet taken at the same time each day starting on day 1-5 of the menstrual cycle with no need for additional protection.
- The POP can be started at any time after day 5 if it is reasonably certain that the individual is not pregnant. Additional precautions are then required for 48 hours after starting and advise to have follow up pregnancy test at 21 days.
- When starting or restarting the POP as quick start after levonorgestrel emergency contraception, additional contraception is required for 48 hours.
- In line with FSRH guidance individuals using hormonal contraception should delay restarting their regular hormonal contraception for 5 days following ulipristal acetate use. Avoidance of pregnancy risk (i.e. use of condoms or abstain from intercourse) should be advised until fully effective.
For guidance on changing from one contraceptive method to another, and when to start after an abortion and postpartum, refer to the Faculty of Sexual and Reproductive Healthcare (FSRH) guidelines
Important facts about POP:
- available evidence has not shown an increased risk of pregnancy in POP users with a heavier body weight or a higher body mass index. There is insufficient evidence to support a dose of more than one pill per day for women who are heavy or overweight
- no evidence suggesting a delay in return of fertility following discontinuation of a POP; therefore if pregnancy is not desired, other contraceptive methods should be used immediately following discontinuation of the POP
- POP can be used until the age of 55 years when natural loss of fertility can be assumed for most women. Alternatively, if they are aged over 50 years and amenorrhoeic they can continue using a POP and have FSH concentrations tested on two occasions 6 weeks apart. If both FSH measurements are >30 IU/l this is suggestive of ovarian failure and they should continue with a POP or barrier method for one further year
- if a woman vomits within 2 hours of pill taking, another pill should be taken as soon as possible. If the subsequent pill is missed, additional precautions are required until 48 hours after pill taking has been resumed
- *while the overall risk of pregnancy is reduced with use of traditional POPs, around 1 in 10 pregnancies that do occur may be ectopic
Reference:
- FSRH (March 2015). Progestogen-only pills.
- Patient Group Direction (PGD) (NHS Specialist Pharmacy Service). Supply of a progestogen only contraceptive pill (POP)