Abstract
It has been known since the 1960s that exogenous progestogens and oestrogens (the pill and hormone replacement therapy (HRT)) increase the risk of both venous and arterial thrombosis. Claims that HRT prevents heart attacks in older women are mostly based on non-randomized epidemiological studies. Healthier women are selected for hormone taking and those with established diseases are excluded, either before or during the studies. Risks may be greatly underestimated. Thrombosis and heart attacks are evident after short-term exposure to hormones and relate mainly to immediate changes in blood vessels and clotting factors. Recent studies record increases of 4-400 times for thrombosis and heart attacks.