Risks and mechanisms of cardiovascular events in users of oral contraceptives.

Three large British studies on the vascular effects of oral contraceptives have established that the risk of thromboembolic episodes, both venous and arterial, rises with increasing estrogen dose. Two of these studies have also demonstrated a dose-dependent relationship between the progestogenic component of oral contraceptives and the risk of arterial disease, though not of venous events. In men, high levels of factor VII coagulant activity, VIIC, and plasma fibrinogen are associated with an increased risk for ischemic heart disease. In view of the dose-dependent relationship between estrogen and these two clotting factors, especially VIIC, it is likely that the effects of oral contraceptive usage on the risk for thromboembolism are mediated substantially through the level of coagulability. The relationship between the progestogenic component of oral contraceptives and the risk for arterial disease is probably related, at least in part, to the effects of progestogens on blood pressure.