Some Birth Control Pills Have Slightly Higher Risk Of Venous Thromboembolism Interview with:
Yana Vinogradova, Research Fellow
Division of Primary Care
School of Medicine
University of Nottingham

Medical Research: What is the background for this study? What are the main findings?

Response: Combined oral contraceptives are an effective method of birth control but do have measurable side effects.  One – common to all combined contraceptives and sometimes fatal – is an increased risk of venous thromboembolism (VTE).  A number of earlier studies investigated VTE risks for different types of hormonal contraceptives, but all were performed some years ago or had insufficient data to analyse newer preparations, while some included only healthy users and others did not adequately control for lifestyle and health issues.  The data used for this study were representative of the UK population and covered all currently prescribed drugs, with results adjusted for the widest possible range of available relevant factors.

We found that the venous thromboembolism risks of combined oral contraceptives appear to fall into two distinct groups.  Newer drugs containing gestodene, desogestrel, drospirenone or cyproterone were associated with risks of VTE between 1.5 and 1.8 times higher than both the older compositions containing norethisterone or levonorgestrel and the relatively newer norgestimate.  While our findings are statistical associations between different compositions and venous thromboembolism risks, they do represent more comprehensive and reliable information for doctors making evidence-based prescribing decisions.

Medical Research: What should clinicians and patients take away from your report?

Response: Combined oral contraceptives remain effective and relatively safe drugs – significantly safer in terms of risk of venous thromboembolism than either pregnancy terminations or pregnancy itself.  Our findings would translate into extra cases of VTE per year of between 6 and 14 per 10,000 treated women.  The findings do suggest, however, that for patients at increased risk of VTE due to other conditions, it may be worth reviewing the formulation of their prescribed pill.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: Venous thromboembolism is a relatively uncommon event and choice of a contraceptive drug can often depend on a woman’s characteristics.  A randomised controlled trial is unlikely to be useful.  A comparable study to this one, which included more detail of actual use (our study measured prescriptions) and which could assemble a more complete and wider range of data for all possible factors affecting venous thromboembolism risks and patient choice, may improve the accuracy and reliability of our findings.  However it would be challenging and expensive to achieve this for the very large number of patients that would be required for such a study.

Citation: Interview with:, & Yana Vinogradova, Research Fellow (2015). Some Birth Control Pills Have Slightly Higher Risk Of Venous Thromboembolism

Last Updated on November 4, 2015 by Marie Benz MD FAAD