It's a quest that never seems to end — the search for a safer birth control pill.
Some thought it might be at hand almost a decade ago when a new generation of oral contraceptives came on the market. They contained a hormone called drospirenone, which some thought would be less likely to cause dangerous blood clots.
Now there's new evidence that the drospirenone-containing pills, sometimes called fourth-generation OCs, may be riskier than the first-generation version that contains a progestin called levonorgestrel.
The Food and Drug Administration this week issued a "safety announcement" prompted by two recent studies, involving hundreds of thousands of British and American women. The studies cast new doubt on drospirenone-containing pills – sold as Yaz, Yasmin, Ocella and a half-dozen other brand names.
And last week the European Medicines Agency updated the labeling of drospirenone OCs to reflect the new data.
The new studies, published last month in the British Medical Journal, found a two- to three-fold higher incidence of serious deep-vein blood clots among women taking drospirenone pills compared to those on the older levonorgestrel contraceptives.
If you want a scorecard, this brings the total number of studies raising doubts about the safety of drospirenone pills to four. Two others (sponsored by Bayer, the maker of the leading drospirenone pills) found no increased risk.
Use of these pills has dropped sharply since 2009, when the first critical studies came out. Thousands of women are suing Bayer over alleged injuries caused by the pills.
A Bayer spokeswoman says the company's "analaysis of the overall body of available scientific evidence continues to support its current assessment about the safety of its oral contraceptives... compared to other birth control pills studied."
Why the discrepancies? I asked Susan Jick, director of the Boston Collaborative Drug Research Program, who said earlier studies weren't careful enough to distinguish between women on contraceptives who suffered blood clots from other causes and those that had no obvious cause — and thus may have been caused by the pill.
"If you limit your study to women who have no other cause for their blood clot – they didn't have a recent surgery or pregnancy or recent injury – you can see the differential effect of blood clots" between those on one kind of pill or another, Jick told Shots.
Jick has a bias; she's a coauthor of both new studies. But she doesn't think drospirenone-containing OCs will be taken off the market – or should be.
"Different women react differently to different contraceptives," Jick says. "There are different kinds of side effects — bloating and other types of things, and certain women feel much better taking one particular kind of pill compared to another, and that has to be taken into consideration as well. So there's the risk and there's the benefit and it's a very personal decision."
She also points out that blood clots are very rare in healthy young women, "and even a doubling or tripling of what is already very rare is still a pretty rare event."
At the same time, she'd tell women she knows that "given there is what I could consider strong evidence that the drospirenone pills do increase the risk of blood clots, they should take the older contraceptives that have been shown to have a lower risk."
There will soon be more evidence on which to base that decision. The FDA has commissioned a study of 800,000 U.S. women on contraceptives and their risk of blood clots. Officials say it should come out sometime this summer.