Blood clots and the contraceptive pill

A blood clot happens when a small part of your blood changes from a liquid to a semi-solid state. Usually, blood can flow freely through the veins, arteries, and smaller blood vessels in the body. This allows oxygen and nutrients to be transported to where they’re needed, powering your cells and keeping your body working normally.

Sometimes this flow of blood can be disrupted by a blood clot. If you’re cut or injured, a blood clot forms to seal the wound and to stop you from bleeding out. This is a good thing.

But a blood clot can also form when it’s not meant to. This makes it harder for blood to flow to the affected area of your body and can cause damage if not addressed promptly.

Many health conditions can be caused by a blood clot, including heart attacks and strokes. Blood clots can also form in your leg, arm, or lungs (pulmonary embolism).

Blood clot risks

3 things can increase the risk of a blood clot forming:

1. Damage to the inside of the blood vessel wall.
2. Blood being more “sticky” or prone to clotting.
3. Pooling of blood within a vein or artery, which disrupts normal flow.

Health conditions, lifestyle, being pregnant, your genes, and even the medications you take (like the contraceptive pill) can all affect these 3 things and increase your risk of a blood clot.

The pill contains synthetic versions of the sex hormones oestrogen and progesterone. The synthetic oestrogens found in the combined pill are known to increase the levels of proteins in the blood that cause clotting. These oestrogens also reduce the levels of proteins that prevent clotting.

Although much of the pro-clotting effects of the pill come from artificial oestrogens, artificial progesterones found in the combined pill also increase the risk of clotting in a similar way.

Taking the combined contraceptive pill could increase your risk of developing a blood clot. Around 1 in 1,000 women taking the combined contraceptive pill develop a blood clot, but the type of pill you take could affect your risk.

Compared with women taking no hormonal contraception, the following types of artificial progesterone increased the risk of blood clots when combined with the artificial oestrogen ethinylestradiol:

• levonorgestrel (found in Microgynon and Rigevidon) - 2.9 x increased risk
• desogestrel (found in Mercilon) - 6.6 x increased risk
• gestodene (found in Femodene) - 6.2 x increased risk
• drospirenone (found in Lucette and Yasmin) - 6.4 x increased risk

Although this sounds scary, it’s important to remember that the risk is still very small when taking the combined pill. The progesterone-only contraceptive pill (mini pill) does not increase your risk of blood clots.

Symptoms of a blood clot depend on the location of the blood clot. Let’s break down the symptoms to watch out for when a blood clot happens in different areas of the body.

Similar symptoms can happen in your arm if a blood clot forms there. If you suspect you have a DVT in your arm or leg, try to book an urgent GP appointment or call 111 for advice.

If you notice any of these symptoms, make an urgent appointment with your GP.

A stroke can be caused by either a blood clot blocking blood flow to 1 area of the brain or by a blood vessel bursting in the brain. Clots are a much more common cause.

Although it’s possible for them to happen, strokes are uncommon in young people – 85 to 90% of strokes happen in people older than 45.

A blood clot is one of the most common causes of a heart attack. Often, the clot forms after fat that’s accumulated in the arteries of the heart breaks off and blocks an artery, but other things can also cause it to happen.

Not everyone having a heart attack experiences these symptoms – sometimes there’s not much pain or it feels more like indigestion.

A blood clot in your arm or leg is usually treated using blood-thinning medications. You may be started on these medications before having an ultrasound scan to confirm whether a clot is present.

If a clot is confirmed, you’ll usually take blood thinners for at least 3 months. In some cases, surgery is also required to remove a blood clot.

A blood clot in the brain or heart will also be confirmed using a scan and/or by measuring the electrical activity in the heart. The clot will then be treated with blood-thinning medication or surgery, too.

Taking the combined contraceptive pill increases your risk of developing a blood clot, but other factors can increase your risk even more, including:

• being overweight
• smoking
• having had a DVT before
• having cancer
• having heart failure
• having varicose veins
• being dehydrated
• having a medical condition that makes your blood prone to clotting
• being immobile for a long time (like after recovering from an operation or travelling for more than 3 hours)

It’s important to discuss all of these things with a healthcare professional before starting the combined contraceptive pill. If they think you’re at a higher risk of clots, they may suggest an alternative form of contraception.

Although it’s good to understand that taking the combined contraceptive pill carries the risks of blood clots, 99.9% of people who take it never get a blood clot.