A study published in The BMJ today suggests a link between newer contraceptive pills and higher risk of serious blood clots. The finding is not new, but it may be cause for a different kind of concern.
During their fertile years, between three and five women of every 10,000 who are not pregnant and not taking the pill are likely to develop blood clots every year. The research published today found older contraceptive pills double this “background” risk of blood clots, and the newer pills have roughly doubled the risk again.
Several studies published over the past 20 years show very similar findings. What this research brings to the table are larger numbers of women and more careful attention to factors in their medical history that could potentially skew the results.
It’s likely the media will pounce on this story; there will be testimonies from women who have experienced blood clots while taking the pill and a plethora of personal injury lawyers spruiking their business. Women across the world will be scared into stopping their contraception until it all blows over. I know this because I’ve seen it before, and I think that’s what we should be concerned about.
Back and forth
We’ve known the pill increases a woman’s risk of blood clots and stroke since it was first marketed. By the 1990s, concern had been tempered by the fact that this risk was greatly reduced by pills containing only a quarter of the oestrogen compared to the 1960s. The development of several newer progestogens in the 1980s had also increased the range of pills available, making it more likely that most women could find a combination that suited them.
But then, in 1995, three studies published in The Lancet suggested pills containing these newer progestogens posed twice the risk of blood clots as the older ones, just as the study published today does. Frenzied media coverage of the finding led many women to simply discontinue their contraception.
As a result, 1995-96 saw a 9% increase in abortion rates in Britain as well as a 25% increase in births. And both pregnancy and birth hold significantly higher risks of blood clots than any contraceptive pill, with rates at least ten times higher.
Within a few years, the controversy settled down somewhat when a number of epidemiologists pointed out that doubling an extremely small risk has no significant public health impact. But then, between 2007 and 2014, it all started again when a number of studies reached conflicting conclusions about whether there were any real differences in clotting rates between various pills.
Annabelle Shemer/Flickr, CC BY-NC-ND
Two very large studies that kept track of women from the time they started various pills showed no difference in blood-clotting risk between any of the pills the women were taking. But research like this is extremely expensive and only within the funding reach of either governments or pharmaceutical companies. In this case, it was the latter. Despite the fact that both studies were independently monitored, they were attacked as having commercial bias.
Four out of six of the remaining studies, which used various databases to look back from a blood clot diagnosis and capture the kind of pill the woman was taking, suggested the newer pills doubled risk. But the inevitable lack of “real-time” information in this kind of research also leaves it open to many potential biases.
The just-published BMJ study provides further evidence for research showing increased risk, and its publication will no doubt re-ignite the debate about the safety of newer contraceptive pills. It’s clearly time for an appraisal of the actual risks involved.
Being cautious
Even if we were to adopt the worst-case scenario from all the studies published to date, being on one of the older versions of the contraceptive pill increases the risk of blood clot from three and five per 10,000 women each year to somewhere between five and eight. Taking one of the newer ones raises it to between nine and 14.
So although a doubling of clotting risk sounds alarming, it actually translates to an additional four to six cases per 10,000 users of the newer pills a year.
It’s also important to recognise that only one in 100 women who have a blood clot will die from it. That risk of death could be cancelled out statistically by driving for two fewer hours each year. Put another way, the risk of a woman dying from a road accident is approximately 25 times that of death from a pill-related clot.
This is not to say we should be blasé about the risks posed by the contraceptive pill. It is above all a medication, which means some of its benefits may be compromised by – potentially serious – side effects. Every woman considering using the contraceptive pill should discuss the risks it poses to her health as well as available alternatives with her prescribing doctor.
This study adds to what is known about blood clot risk on various oral contraceptive pills, but it doesn’t claim to provide the definitive answer. I hope that, as we again debate the risks posed by the pill, we don’t lose sight of the fact that, for most women, the benefits of combined contraceptives far outweigh risks.
Terri Foran is Lecturer in the School of Women’s and Children’s Health at UNSW Australia.
This article was originally published on The Conversation.
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