Another Example of Evidence Changing Over Time

Posted by The Evidence Blog on June 11, 2015

When we evaluate healthcare technologies, we examine and synthesize the entire body of research evidence that exists at that particular moment in time. Analyzing all the available evidence, rather than simply cherry picking selected publications, enables us to draw accurate, reliable, and useful conclusions about the safety and efficacy of the healthcare technology we are investigating.

Of course, the body of evidence is not static; new information accumulates over time. Safety issues, in particular, often do not become apparent until large numbers of people have taken a drug or used a particular healthcare product or service.

Take, for example, modern oral contraceptives that are formulated with the synthetic progestogen hormones drospirenone, gestodene, cyproterone, and desogestrel. These products were designed to be safer for women than older versions and physicians prescribed them for that very reason. However, the results of an observational study just published in the British Medical Journal (BMJ) show that these birth-control pills actually significantly increase the risk of harmful blood clots compared with earlier options.

For decades we have known that oral contraceptives are associated with an increased risk of blood clots. This latest study, however, quantifies the links between use of combined oral contraceptives and risk of blood clots for newer types of formulations, with adjustments made for comorbidities and other confounding factors. The next step is to ensure that women and prescribers understand the implications of these results so they can make informed, evidence-based decisions about their contraceptive choices.

Will oral-contraceptive prescribing patterns change with this new evidence? We will have to wait and see. We certainly hope prescribers will consider these study results and incorporate this evidence into practice. But despite all the emphasis on evidence-based medicine and discussions about the importance of evidence as the foundation for healthcare decision making, “talk” doesn’t necessarily align with or predict behavior.

Topics: Hayes Blog

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