Oral contraceptives and thrombosis.

Recent studies have identified an increased risk of venous thromboembolism associated with use of third-generation oral contraceptives (OCs). Use of these newer formulations has been estimated to cause an excess of 10 deaths/year in the UK. The possibility has been raised however that prescribing bias and confounding by duration of OC use and other personal risk factors accounts for the difference in the risk of venous thromboembolism between second- and third-generation OCs. Other studies have identified an increased risk of myocardial infarction and stroke in OC users including users of low-dose formulations but this risk is almost exclusively limited to older women who smoke or have other cardiovascular risk factors. The interpretation of all such studies on OC side effects should take into account that the absolute risk of an adverse thrombotic event while taking OCs is small. This risk appears to be affected far more by factors such as smoking age hypertension and familial disorders than the type of progestagen contained in the OC.