Oral contraceptives, hormone replacement therapy and thrombosis

Oral contraceptives and hormone replacement therapy are used by hundreds of millions of women worldwide. Since the early 1960s it is known that female hormones increase the risk of venous thrombosis, myocardial infarction and stroke. This risk is still present with current low-dose oral contraceptiv es and, even though in absolute terms the risk is small, oral contraceptive s form the major cause of thrombotic disease in young women. The risk is hi gher during the first year of use (up to 1 per 1000 per year), with the use of desogestrel- or gestodene-containing oral contraceptives ("third genera tion progestogens") and among women with a prothrombotic predispositon. Hor mone replacement therapy increases the risk of venous thrombosis, while res ults of randomised trials so far do not substantiate the expectation of a b eneficial effect on the risk of arterial cardiovascular disease. First resu lts are emerging that specific subgroups of women, with prothrombotic or ot her abnormalities, may be at risk, especially during the first years of use of hormone substitution.