"Epidemiological studies by the Medical Research Council, in the UK, revealed that pill users were more susceptible than nonusers to thromboembolism9. On second thoughts, this complication could be anticipated because of the established link between high oestrogen levels and thromboembolism during pregnancy. Later, it was shown that oestrogens and ethinylestradiol in particular stimulate the synthesis of several clotting factors and hepatic proteins among which the renin substrate angiotensinogen, re-sponsible for pill-induced hypertension in susceptible women. This first pill scare led to the gradual reduction in the dosage of ethinylestradiol from 50 to 30, 20 and even 15 μg. This dose reduction was associated with less side effects such as breast tenderness, nausea and bloating. But, even at these low doses, oral contraceptives still exert a prothrombotic effect."