Unfortunately there is a fair amount of confusion regarding this little pill, largely because of its name. Many people believe that the lower-dose combined (oestrogen and progesterone) pills are in fact ‘minipills’. Not so.
The true ‘minipill’, or the ‘progesterone-only pill’ (POP) has been used widely as the pill taken for contraception while breastfeeding (lactating). Together with the natural (but not always reliable) contraceptive effect of lactation the POP gives further protection, without interfering with milk production.
Lactation naturally suppresses ovulation. The World Health Organisation has collated research and has stated that if a baby is under six months old and is fully breast fed (with no additional or formula feeding), and the mother is not having periods, then the chance of the woman becoming pregnant is about 2 per cent. When any of these criteria are not fulfilled, the risk of pregnancy increases significantly. (That is why the minipill is handy.)
However, its usefulness extends further than simply with lactation. It can been used by women who, for a variety of reasons, cannot take oestrogens (and therefore can’t take the combined pill).
It acts by increasing the mucus plug at the cervix, making it much more difficult for sperm to penetrate. It also probably slows down the transport mechanisms in the tubes, so the sperm are less likely to find a comfy place to fertilise and settle. It’s a bit like a picket line, and if a strike breaker does happen to get through, the factory is on a ‘go slow’ campaign.
The failure rate of the POP is about two to three per 100 women years, not bad, but not as good as the combined pill (but with fewer serious side-effects). Because it has narrower safety margin it is even more important to take care not to miss any tablets, or to delay taking them. Problems like vomiting and diarrhoea and antibiotic use can interfere with absorption and effectiveness of the POP, as they can for the combined oral contraceptive pill. You should take added precautions (like condoms or abstain from sex) for the time of increased risk, and for at least two (rather than seven) days after, to avoid getting pregnant.
The POP does not have the advantages of cycle control, and in fact spotting, irregular cycles and missed periods can be a problem for some POP-takers. Apart from this, the only other significant side-effect is that some women can experience mood problems (mild depression, PMS-type symptoms) while taking the POP, but this is uncommon as it is such a small dose of progesterone.
However, it is an extremely useful, and probably under-utilised form of contraception. Used alone it provides fairly effective pregnancy prevention (when used properly). It is more effective when combined with another method, like breast feeding or barrier methods.
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