The estrogen components of the study were terminated early because of increased incidence of thromboembolism and nonfatal myocardial infarction. It should be noted that the test subjects were elderly males with a known history of coronary disease. No controls were established with regard to other cardiovascular treatment, especially aspirin use and cigarette smoking. These results should not be extrapolated to the younger, healthy transsexual population. This is a good reason to counsel transsexual patients against taking excessive doses of estrogen.
Lower doses are much less dangerous.
In low doses, estrogen inhibits platelet aggregation and reduces PAI-1, plasminogen activator inhibitor. This promotes thrombolysis and helps to dissolve smaller intravascular thrombi. Certain persons may have an increased risk for spontaneous thromboembolic disorders. The Leiden Factor V mutation occurs in 2 per cent of the population and increases risk of thrombosis 30 fold in women on oral contraceptives. These may be the persons who experience complications on low dose estrogen.