Contrary to the results of a widely reported study showing an increased risk of blood clots in women using the Ortho Evra birth control patch over those taking a birth control pill, research done at Boston University suggests that women using the patch have no greater risk of developing blood clots than women taking oral contraceptives.
Susan Jick, an associate professor of epidemiology and biostatistics at the School of Public Health, and lead author of the BU study, says conflicting research reported last week in the New York Times is not complete, has not been published, and its methodologies have not been disclosed. That ongoing study, conducted by i3 Drug Safety, issued an interim report last week showing a twofold increase in the risk of venous thromboembolic events (VTE) for women on the patch compared with women on oral contraceptives. Both studies were sponsored by Johnson and Johnson, the maker of the patch.
Jick’s work was conducted with James Kaye, an SPH associate professor of epidemiology, Stefan Russmann, an SPH assistant professor of epidemiology, and Hershel Jick, a School of Medicine associate professor of medicine, as part of MED’s Boston Collaborative Drug Surveillance Program (BCDSP). Their study was published last week in the journal Contraception.
Jick says that it has been known for many years that taking oral contraceptives increases the risk of developing blood clots. When the patch became available in 2002, some women who were using it reported developing such clots. But, says Jick, “spontaneous reports” of a condition often peak when a drug is new, particularly if that condition represents a “known risk factor.”
As many as five million American women have used the patch. Manufacturer Johnson and Johnson was asked by the U.S. Food and Drug Administration to study whether the patch was any more likely than oral contraceptives to cause VTE, stroke, or heart attack.
According to Jick, some estimates and anecdotal evidence had suggested that patch-users were three times more likely to develop VTE. She says the BCDSP study, which involved more than 200,000 women, showed the risks are the same as for users on the pill.
“We feel our study is very reassuring,” she says, adding that their research also considered other factors that contribute to the risk for developing VTE, such as age, duration of treatment, diabetes, or heart disease. To control for calendar time and duration, the study examined women who were using either the contraceptive patch or an oral contraceptive containing ethinyl estradiol and the progestin norgestimate beginning in April 2002 through March 2005. Results show that women over 40 were more than 10 times as likely to be diagnosed with VTE than women under 20.
In the past 35 years, the BCDSP has published more than 20 papers on the safety of oral contraceptives; this is the program’s first study on contraceptives funded by the pharmaceutical industry.