The pill and blood-clot (VTE) risk, in proportion

The link between the combined pill and blood clots is the safety issue people worry about most, and it is right to take it seriously. But worry tends to run ahead of the actual numbers.

This article lays out the real risk, sets it against everyday comparisons, and explains who needs to be especially careful.

What a VTE actually is

VTE stands for venous thromboembolism, a blood clot that forms in a vein. The two main types are a deep vein thrombosis, or DVT, usually in the leg, and a pulmonary embolism, or PE, where a clot travels to the lungs. A PE is the serious one. VTE is uncommon in young, healthy people, but oestrogen nudges the risk up, which is why it matters for the combined pill.

The numbers, in proportion

It helps to use the same unit throughout: cases per 10,000 women in a year.

Not pregnant and not on the combined pill: the background rate is about 2 in 10,000 per year.

On a combined pill: the rate is roughly 5 to 12 in 10,000 per year, depending on which progestogen it contains. Pills with levonorgestrel sit at the lower end, some others a little higher.

During pregnancy: the rate is about 29 in 10,000, and it is higher still in the first weeks after giving birth.

In other words, the combined pill raises the risk above baseline, but the risk is lower than the risk that comes with pregnancy itself. For most healthy people, the absolute chance of a clot remains small.

To put it another way, if 10,000 women take a combined pill for a year, more than 9,980 of them will have no clot at all. The increase is real and worth screening for, but it is small in absolute terms.

What about the progestogen-only options?

It is worth being clear that this clot risk is specific to the oestrogen in the combined pill. The progestogen-only pill, the implant, the hormonal coil, and the injection do not carry the same increase in VTE risk. So if you have a personal or family history that makes the combined pill a poor choice, you are not left without good contraception. You simply move to one of the oestrogen-free options, which are just as effective at preventing pregnancy.

What raises your personal risk

The pill is one factor among several, and they add up. Risk is higher if you have had a clot before, if you have an inherited clotting condition such as factor V Leiden, if you are over 35, if you smoke, if you have a high body mass index, if you are immobile for a long stretch such as a long-haul flight or recovery from surgery, or if a close relative had a clot at a young age. The assessment exists to spot these combinations before they matter.

How we keep the risk low

Two things make the biggest difference. First, screening you properly before prescribing, so that anyone for whom the combined pill is genuinely risky is steered to a progestogen-only pill instead, which does not carry this clot risk. Second, choosing a lower-risk formulation where the combined pill is suitable. We also flag situations, such as major surgery or a long period of immobility, where it can make sense to pause a combined pill temporarily.

Knowing the warning signs

Whatever pill you are on, it is worth knowing the signs of a clot so you can act fast. A DVT typically causes pain, swelling, warmth, or redness in one leg, often the calf. A PE causes breathlessness, chest pain that is worse when you breathe in, or coughing. If you have these, treat it as urgent and seek medical help straight away.

Putting it in perspective

The combined pill is one of the most studied medicines in the world, and for healthy people without the risk factors above the clot risk is small and the benefits often outweigh it. The point of the safety screen is not to frighten you off, it is to make sure the small group for whom the risk is not worth taking are offered something safer. If oestrogen is not right for you, the progestogen-only pill removes this particular risk entirely.

Ready to start?

If you want to move from reading to acting, the next step is a short, confidential assessment with one of our doctors. No judgement, no assumptions.

Begin your assessment at this link. Online or in person at Westfield London.