Progestogen-only pills and the modern 24-hour window

The progestogen-only pill, or POP, used to have a reputation for being fiddly and easy to get wrong. That reputation belongs to an older generation of pill. The versions prescribed today are more reliable and much more forgiving about timing.

For anyone who cannot or would rather not take oestrogen, the POP is an excellent option. This article explains how it has changed.

What is in it, and how it works

The progestogen-only pill contains a single hormone and no oestrogen, and you take one every day with no break between packets. Depending on the type it works by thickening cervical mucus so sperm cannot get through, and the most common modern type, desogestrel, also stops ovulation in most cycles. Taken correctly it is more than 99 percent effective.

When you stop it, your fertility returns quickly, often within days to weeks, because it clears from your system fast. As with the combined pill, there is no need to take breaks from it for your health.

The three generations, and why the window matters

The window is how late you can be with a pill before you are no longer protected and need extra precautions. It is the single biggest practical difference between the types.

The old mini-pills, levonorgestrel and norethisterone, have a strict 3-hour window. Miss it and you need backup. These are rarely the first choice now.

Desogestrel pills have a 12-hour window, which is far more workable for everyday life. This is the most widely prescribed POP.

The drospirenone-only pill has a 24-hour window, and is taken as 24 active pills followed by 4 hormone-free days. A full day of leeway makes it the most forgiving pill of all to take.

Who the POP suits

The progestogen-only pill is the natural choice when oestrogen is not suitable: while breastfeeding, after a blood clot, for migraine with aura, and for those over 35 who smoke. It is also a good option simply if you prefer to avoid oestrogen, or if a combined pill gave you side effects you would rather not repeat.

The honest part: bleeding patterns

The main trade-off is unpredictable bleeding, especially in the first few months. Roughly speaking, about two in ten people stop bleeding altogether, a similar number get frequent or prolonged bleeding, and the rest land somewhere in between. For many the pattern settles by three to six months. There is no reliable way to predict in advance which group you will be in, so it is worth giving it a fair trial before judging it.

It is also worth saying that irregular bleeding on the progestogen-only pill is not a sign that it is failing, and it is not harmful. It is simply how the lining of the womb responds to a steady low dose of progestogen.

A few things that affect how well it works

Like any pill, the progestogen-only pill can be less effective if you are sick or have diarrhoea within a couple of hours of taking it, or if you take certain medicines that speed up how your liver clears hormones, such as some epilepsy treatments and the herbal remedy St John's wort. Most everyday medicines, including most antibiotics, do not interfere with it. If you start a new long-term medication, it is worth checking whether it interacts. Otherwise the main thing within your control is simply taking it within its window each day.

What to do if you miss one

If you are later than your pill's window, take the missed pill as soon as you remember, take the next one at the usual time, and use condoms or avoid sex for the next two days. If you had unprotected sex during that gap, emergency contraception may be needed. Sickness and diarrhoea can also stop a pill being absorbed, so the same backup applies.

Not the right pill for you if...

If a predictable monthly bleed is important to you, the combined pill, if you can take it, gives you that and the POP usually does not. If irregular bleeding would worry you a great deal, it is worth weighing that up before starting. And if remembering a daily pill at all is the real problem, a long-acting method may serve you better.

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