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21st Apr 2021

Everyone’s talking about blood clots and the pill – here’s what you should know

Laura Cunningham

The pausing of certain Covid-19 vaccines because of a risk of clotting has lead many to make comparisons with the contraceptive pill.

6.8 million Johnson & Johnson vaccines were administered in the U.S. in recent weeks, to help halt the spread of Covid 19. Six women subsequently experienced blood clotting after receiving the single-dose vaccine, leading to a temporary halt on its rollout.

A huge 25 million people received the AstraZeneca vaccine in the UK. As of the end of March, 79 of them had suffered rare blood clots.

Although territories have paused or stopped certain vaccines to err on the side of caution, many too have established that clotting is a medically rare side effect for certain age groups, and that the overall benefit-risk ratio remains positive.

But how do those figures stack up against the risk of clotting when taking the contraceptive pill?

According to Healthline, in 2012 the FDA reported that out of every 10,000 women using birth control for one year, three to nine of them would develop a blood clot.

However, to put that into context, out of every 10,000 women who do not take a contraceptive pill, one to five of them will develop a blood clot.

That increase may be small, but why does this happen?

The estrogen combination in certain hormonal birth control methods increases the risk of a blood clot in the leg, or deep vein thrombosis. It also increases the chance of blood clot in the lung, or a pulmonary embolism. According to Michigan Medicine, “a blood clot in a leg vein can travel through the circulatory system and cause pulmonary embolism.”

While the overall risk for deep vein thrombosis or a pulmonary embolism is relatively low with hormonal contraceptives, birth control that contains a higher dose of estrogen can slightly increase the risk of both again.

So, is the pill safe?

Although the risk is deemed to be small, anybody considering taking the contraceptive pill should of course talk to their doctor about any family history of clotting or blood disorders and they will establish which contraceptive method is safest for you.

You can find more information from the HSE on the risks involved in taking the contraception pill here.