Newer Contraceptive Pills Tied to Higher VTE Risk, Again

All contraceptive pills carry an increased risk for venous thromboembolism (VTE), but the newer ones are actually riskier, according to a combined population-based, nested case-control study published online May 26 in the BMJ.

Results of the study, the largest on this topic to date, showed that oral contraceptives containing a newer progestogen (desogestrel, gestodene, drospirenone, or cyproterone) had about double the risk of those containing an older one (levonorgestrel or norethisterone). The newer agent norgestimate was the exception.

"This study, based on national population and prescribing practices in the UK, has sufficient power to provide reliable comparative findings for different formulations of combined oral contraceptives," write Yana Vinogradova, MSc, a research fellow in medical statistics, Division of Primary Care, University Park, in Nottingham, and colleagues.

"The results from our study and [a Danish national cohort study] provide evidence for relevant authorities concerned with prescribing guidelines or those involved with regulation of safety of medicines."

In a journal news release, the researchers emphasize that oral contraceptives are remarkably safe and note that the observed elevation of VTE risk in the study is still far less than the up to 10-fold elevation of risk associated with pregnancy.

Current users of combined oral contraceptives "should not stop using them, but should consult their doctor and review their current type of pill at their next appointment if there are any concerns," they recommend.

In an accompanying editorial, Susan S. Jick, DSc, a professor of epidemiology from the Boston Collaborative Drug Surveillance Program, Boston University School of Public Health, Lexington, Massachusetts, writes, "[T]he results provide compelling evidence that these newer oral contraceptives are associated with a higher risk of venous thromboembolism than older options, despite attempts to develop safer hormonal contraceptives for women."

She adds, "These results, combined with those published in [the similar Danish study], clarify inconsistencies in earlier studies and provide important guidance for the safe prescribing of oral contraceptives."

Risk Increased Nearly Threefold

Vinogradova and colleagues analyzed data from UK general practices captured in the Clinical Practice Research Datalink and the QResearch primary care database. They identified 10,562 women aged 15 to 49 years who had a first VTE diagnosis between 2001 and 2013 and matched them by age, practice, and calendar year with 42,034 women who had not had a VTE.

In adjusted analyses, current users (those with use in the past 28 days, based on prescriptions) of any combined oral contraceptive had an elevated risk for VTE compared with counterparts with no such use in the past year (odds ratio, 2.97).