Progestogen-only Contraceptive Pill

Synonyms: POP, mini-pill

• Ovulation is inhibited in about 60% of cycles² although it does not occur in 100% of cycles without hormonal contraception. With desogestrel ovulation is inhibited in 97% of cycles.³
• Transport of the ovum is delayed
• The cervical mucus becomes more viscous and impenetrable to sperm
• The endometrium is unsuitable for implantation.

• It is an effective and safe form of contraception, and is often used when combined pill contraindicated - e.g. venous thromboembolism, or past history or tendency to venous thromboembolism.
• It contains an even lower dose of progestogen than low-dose combined contraceptives, and no oestrogen.
• It is a suitable alternative for those over 35 who need to be changed from a COC, heavy smokers, those with hypertension, valvular heart disease, diabetes mellitus, migraine.There is however very little data on cardiovascular risk and the POP.
• It can be used during breast feeding
• It is suitable for women with valvular heart disease, and those about to undergo major surgery or surgery on their legs.
• It is suitable for those who want a minimal dose of hormone as it gives a very low dose
• It can be used by those who must not take oestrogens for various reasons like a history of deep vein thrombosis or migraine with aura.

• The failure rate is slightly higher than with a COC with a method failure rate of 0.5% compared with 0.1% for the COC. This is the per centage of unintended pregnancies in the first year of use. However, user failure rate pushes both up to 5%.
• It has to be taken meticulously at the same time each day. The error for forgotten pills is just 3 hours late for POPs with the exception of Cerazette that has a licence for 12 hours.
• It is just as susceptible to substances that cause enzyme induction like rifampicin, many anticonvulsants and St John's wort. It is not affected by broad spectrum antibiotics.
• It does not give the regulation of menstruation of the COC, including its tendency to alleviate symptoms of PMT, dysmenorrhoea and making menstruation lighter. It may produce irregular menstruation or amenorrhoea. This may be trouble enough for some to lead to cessation of the method. If oestrogen levels fall and cause amenorrhoea there may be concern that there is a risk of osteoporosis. This has been considered in relation to depot and implant contraception. An overview of the relationship between use of progestogen-only contraceptives and bone mineral density found remarkably little evidence about this in users of the POP.⁴
• There is an increased risk of ovarian cysts, perhaps up to 30%. They are usually reversible and do not require operation.
• The data on the risk of breast cancer is unreliable because of small numbers but it may be that the risk is small but finite as with the COC. After stopping the method the risk disappears after 10 years.⁵
• It is no less effective in women weighing over 70kg.⁶

• The POP must not be used in the presence of breast cancer as this is a hormone dependent tumour. It may be considered if there has been no evidence of disease for 5 years if other methods do not seem acceptable.
• The risk of thromboembolism is much less than with the COC but in the presence of deep vein thrombosis or pulmonary embolism it should be avoided.
• There is concern about reduction in the levels of HDL, although this may be less marked with the newer progestogens. Hence they are better avoided in established CHD or stroke.
• As with any other form of hormonal contraception it should be avoided in liver disease.

• It is usually started on the first day of menstruation and then no additional contraceptive is required.
• After childbirth it can be started on day 21. There is no need for contraception before then and the risk of intermenstrual bleeding is increased by starting earlier. WHO recommend waiting until 6 weeks postpartum if breastfeeding and using an alternative method for the extra 3 weeks. This is because of hormones getting into the milk and hence the baby.
• It can be started immediately after termination of pregnancy in any trimester and it is immediately effective.
• If changing from a COC to a POP, start at the end of a COC pack, moving straight on from the last COC pill to the POP the following day. If the COC is an ED (every day) pack then start after the last active pill.
• Pills must be taken about the same time each day. It is regarded as late if it is taken more than 3 hours after the usual time or 12 hours with Cerazette. The missed pill should be taken as soon as possible. The subsequent pills should be taken as usual but additional contraception should be used until pills have been taken correctly for 2 days.
• Vomiting or severe diarrhoea may impair absorption of the hormone. Additional contraception should be used during this phase and for 7 days after
• Irregular menstrual pattern may settle with time or a change to a different formulation.

Desogestrel is a newer progestogen that is converted in the body to the active form of etonogestrel. The only contraceptive pill containing desogestrel currently licensed in the UK is Cerazette.⁷ Desogestrel tends to be metabolically "cleaner" than the older progestogens and appears very promising. Amenorrhoea is more likely to occur, being present in 50% of desogestrel users compared with 10% of those taking levonorgestrel in one study.⁸ Failure rate was also lower with desogestrel but the numbers were so small that confidence intervals were very wide and there was considerable overlap. The feature of this formulation that is likely to have the greatest impact is the 12 hours window for "forgetfulness" rather than just 3 hours.⁹