Progestogen-only pills: traditional, desogestrel and drospirenone
A progestogen-only pill has a progestogen (a hormone that acts like progesterone) but no oestrogen, and comes as traditional, desogestrel or drospirenone types.
Remember
When oestrogen is ruled out, a progestogen-only pill remains an option, and the drospirenone type allows the longest delay (24 hours) before a late tablet may reduce protection, ahead of desogestrel (12 hours) and traditional pills (3 hours).
Memory aid
3, 12, 24
The numbers give the missed-pill windows in hours for the traditional, desogestrel and drospirenone pills, each longer than the last.
A progestogen-only pill (POP) contains a progestogen and no oestrogen. It is suitable for almost all women, including breastfeeding mothers, smokers over 35 and women with migraine with aura (migraine preceded by temporary warning symptoms known as aura). Combined pills, which add oestrogen, are ruled out when there is aura, because they are linked to small absolute increases in events such as stroke.
Three types are available in the UK: traditional pills differ from desogestrel and drospirenone pills in their main mechanism, and the three types differ from one another in the missed-pill window (how late a tablet can be taken while still giving full protection). Traditional pills (norethisterone or levonorgestrel) work mainly by thickening cervical mucus (the mucus at the neck of the womb), so that sperm struggle to pass. Ovulation inhibition is less reliable, and the window is 3 hours. Desogestrel pills mainly inhibit ovulation (stopping the ovary releasing an egg), with extra mucus thickening, and allow 12 hours. Drospirenone pills also mainly inhibit ovulation and allow 24 hours. Each drospirenone pack holds 24 active tablets followed by four inactive ones, the hormone-free interval.
The windows grow in the order 3, 12, 24 hours, so a drospirenone pill gives the widest margin for someone working shifts. All progestogen-only pills can change the bleeding pattern, so periods may be lighter, more frequent, irregular or stop.
Key facts
- Traditional pill
- works mainly by thickening cervical mucus, ovulation inhibition is less reliable, and the missed-pill window is 3 hours.
- Desogestrel pill
- mainly inhibits ovulation, with extra cervical mucus thickening, and has a 12-hour missed-pill window.
- Drospirenone pill
- mainly inhibits ovulation and has a 24-hour missed-pill window, with a hormone-free interval of four inactive tablets in each pack.
- No oestrogen
- progestogen-only pills contain no oestrogen, so they remain suitable in breastfeeding, in migraine with aura and in smokers over 35.
- Combined pills
- migraine with aura is a UKMEC category 4 contraindication to combined hormonal contraception (UKMEC is the UK Medical Eligibility Criteria, where 4 means unacceptable risk, do not use).
- Bleeding
- all progestogen-only pills can change the bleeding pattern, so periods may be lighter, more frequent, irregular or stop.
Exam traps
- A desogestrel pill does not allow 24 hours for a late tablet, because its missed-pill window is 12 hours; the 24-hour window belongs to the drospirenone pill.
- Desogestrel pills do not work mainly by thickening cervical mucus, because they mainly inhibit ovulation; mucus thickening as the main effect is the hallmark of traditional pills, which allow 3 hours.
- Smoking at 35 or over does not rule out progestogen-only pills, because they contain no oestrogen; it is the combined pills, which contain oestrogen, that are ruled out for someone who smokes 15 or more cigarettes a day at that age.
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