Using epidemiological data to guide clinical practice: review of studies on cardiovascular disease and use of combined oral contraceptives.

OBJECTIVE To explore the usefulness of epidemiological data to guide clinical practice by seeking an answer to the question "What is the risk of cardiovascular disease among users of currently available, low dose, combined oral contraceptives who are aged less than 35 years, do not smoke, and do not have a medical condition known to increase the risk of vascular disease?" DESIGN Review of all relevant published studies identified from the library of references held by Royal College of General Practitioners' Manchester Research Unit, checking of reference lists of identified studies, and Medline search. MAIN OUTCOME MEASURES Identification of methodologically sound studies able to address the specific clinical question. RESULTS Our literature search identified 74 papers about the relation between current use of combined oral contraceptives and cardiovascular disease: 23 papers reporting risk of venous thromboembolism, 22 on ischaemic stroke, 13 on haemorrhagic stroke or subarachnoid haemorrhage, 13 on all stroke, and 33 on myocardial infarction. Only five papers provided information that directly addressed our clinical question; all related to the risk of venous thromboembolism. Fourteen of the discarded papers probably had the potential to answer our clinical question. CONCLUSIONS Much of the epidemiological data about the risk of cardiovascular disease in users of combined oral contraceptives is not useful to clinicians. Some of the discarded data could be made more useful to clinicians by reanalysis. This situation is unlikely to be unique to use of contraceptives.