Two studies published in this weeks’ British Medical Journal, one from the US and the other from the UK, report that users of drosperinone containing oral contraceptives (Yaz, Yasmin and their generics) have increased relative risks for non-fatal blood clots compared with users of pills containing levonorgestrel.
While neither study is perfect, and indeed have some very major limitations, they add to a growing body of evidence that pills containing drosperinone may impart higher risks for blood clots than older pills. Yaz is not alone in this regard – other studies have suggested that pills containing the newer progestins gestodene and desogestrel also impart slightly high clot risks than the so-called first and second generation pills containing the older progestins norethindrone and levonorgestrel.
I won’t go into the studies’ limitations here, but will say that trying to get our hands around comparative data on clot risks between various pills is an extraordinarily difficult process given that the diagnosis of blood clots is not always straightforward (or correct), pill choices are not randomized and fraught with prescribing bias, and confounding risk factors for clotting are numerous and difficult to control for. I wish folks would stop trying to answer these questions on the quick and cheap using claims and pharmacy databases without requiring chart review and strict diagnostic criteria. But that’s the way these studies are being done, and that’s the data I am being forced to contend with in my practice, so let’s talk about it.
Just how high is the blod clot risk from Yaz?
Actually, it’s quite small – far, far less than a 1% chance or even a 1 in a thousand chance. According to the US Study, if 100,000 women were to use the pill for a year, clots would occur in 23 Yasmin vs 9.1 levonorgestel containing pill users. In the UK study, corresponding risks were 30.8 for drosperinone vs 12.5 for levonogrestrel-containing pills.
If you are taking Yaz or Yasmin, should you change your pills?
Not necessarily. Most clots occur in the early months of pill use, so if a woman has been using Yaz or Yasmin for longer than a year or so, she’s pretty much defined herself as low risk, and changing to a different pill is not going to lower her odds much further. Talk to your doctor about your concerns and choices.